Tag Archives: Atmospheric and Oceanic Physics

Global Weather for the Astronomical Observatories [IMA]

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http://arxiv.org/abs/2110.01206


Astronomical sites occupying observing instruments have to be selected according to many factors. Among these factors, geographic location of the site and quality of atmosphere above the site play an important role in the decision process. The following factors were chosen to create layers at their geographic locations (observatories: 1905 northern, 235 southern) from the \href{https://www.astrogis.org}{astroGIS database}: CC (cloud coverage), PWV (precipitable water vapor), AOD (atmospheric optical depth), VWV (vertical wind velocity) and HWV (horizontal wind velocity). In order to estimate astronomical importance of geographic location of the sites and quality of airmass above the sites, DEM (digital elevation model) and LAT (latitude of observatory location) layers were also included. Two periodic variations have been produced from these factors: monthly and annual averages. In addition to the variations or trends a complete statistical analysis was carried out for all factors to investigate the potential correlations between the factors: There is a clear difference between northern and southern hemispheres. Exchange of meteorological seasons between hemispheres are also compliant within factors. The geographical locations of most of the observatories found to be “not suitable”: On the average, DEM is low (550 m), CC is high (70\%) and PWV is high (14 mm). There seems to be no apparent long-term variations and/or patterns in all factors. We once again confirm the common expectation of astronomy: \textit{as DEM increases astronomical conditions get better} (CC, PWV and AOD gets lower values). All the results will be made available online through astroGIS database.

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Z. Kurt, S. Yerli, N. Aksaker, et. al.
Tue, 5 Oct 21
33/72

Comments: 14 pages, 5 tables, 6 figures, Submitted to MNRAS

Large-scale Vortices in Rapidly Rotating Rayleigh-Bénard Convection at Small Prandtl number [CL]

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http://arxiv.org/abs/2109.14289


One prominent feature in the atmospheres of Jupiter and Saturn is the appearance of large-scale vortices. However, the sustaining mechanism of these large-scale vortices remains unclear. One possible mechanism is that these large-scale vortices are driven by rotating convection. Here we present numerical simulation results on rapidly rotating Rayleigh-B\’enard convection at a small Prandtl number $Pr=0.1$ (close to the turbulent Prandtl numbers of Jupiter and Saturn). We have identified four flow regimes in our simulation: multiple small vortices, coexisted large-scale cyclone and anticyclone, large-scale cyclone, and turbulence. The formation of large-scale vortices requires two conditions to be satisfied: the vertical Reynolds number is large ($Re_{z}\ge 400$), and the Rossby number is small ($Ro\leq 0.4$). Large-scale cyclone first appears when $Ro$ decreases to be smaller than 0.4. When $Ro$ further decreases to be smaller than 0.1, coexisted large-scale anticyclone emerges. We have studied the heat transfer in rapidly rotating convection. The result reveals that the heat transfer is more efficient in the anticyclonic region than in the cyclonic region. Besides, we find that 2D effect increases and 3D effect decreases in transporting convective flux as rotation rate increases. We find that aspect ratio has an effect on the critical Rossby number for the emergence of large-scale vortices. Our results provide helpful insights on understanding the dynamics of large-scale vortices in gas giants.

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T. Cai
Thu, 30 Sep 21
70/82

Comments: Accepted to ApJ

Analytical Solution of Similar Oblate Spheroidal Coordinate System [GA]

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http://arxiv.org/abs/2109.12057


Satisfactory description of gravitational and gravity potentials is needed for a proper modelling of a wide spectrum of physical problems on various size scales, ranging from atmosphere dynamics up to the movements of stars in a galaxy. In certain cases, Similar Oblate Spheroidal (SOS) coordinate system can be of advantage for such modelling tasks, mainly inside or in the vicinity of oblate spheroidal objects (planets, stars, galaxies). Although the solution of the relevant expressions for the SOS system cannot be written in a closed form, it can be derived as analytical expressions — convergent infinite power series. Explicit analytical expressions for the Cartesian coordinates in terms of the curvilinear Similar Oblate Spheroidal coordinates are derived in the form of infinite power series with generalized binomial coefficients. The corresponding partial derivatives are found in a suitable form, further enabling derivation of the metric scale factors necessary for differential operations. The terms containing derivatives of the metric scale factors in the velocity advection term of the momentum equation in SOS coordinate system are expressed. The Jacobian determinant is derived as well. The presented analytical solution of SOS coordinate system solution is a tool applicable for a broad variety of objects exhibiting density, gravity or gravitation levels resembling similar oblate spheroids. Such objects range from the bodies with small oblateness (the Earth itself on the first place), through elliptical galaxies up to significantly flattened objects like disk galaxies.

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P. Strunz
Mon, 27 Sep 21
29/68

Comments: 42 pages, 5 Postscript figures

The TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI). Part II: Moist Cases — The Two Waterworlds [EPA]

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http://arxiv.org/abs/2109.11459


To identify promising exoplanets for atmospheric characterization and to make the best use of observational data, a thorough understanding of their atmospheres is needed. 3D general circulation models (GCMs) are one of the most comprehensive tools available for this task and will be used to interpret observations of temperate rocky exoplanets. Due to various parameterization choices made in GCMs, they can produce different results, even for the same planet. Employing four widely-used exoplanetary GCMs — ExoCAM, LMD-Generic, ROCKE-3D and the UM — we continue the TRAPPIST-1 Habitable Atmosphere Intercomparison by modeling aquaplanet climates of TRAPPIST-1e with a moist atmosphere dominated by either nitrogen or carbon dioxide. Although the GCMs disagree on the details of the simulated regimes, they all predict a temperate climate with neither of the two cases pushed out of the habitable state. Nevertheless, the inter-model spread in the global mean surface temperature is non-negligible: 14 K and 24 K in the nitrogen and carbon dioxide dominated case, respectively. We find substantial inter-model differences in moist variables, with the smallest amount of clouds in LMD-Generic and the largest in ROCKE-3D. ExoCAM predicts the warmest climate for both cases and thus has the highest water vapor content, the largest amount and variability of cloud condensate. The UM tends to produce colder conditions, especially in the nitrogen-dominated case due to a strong negative cloud radiative effect on the day side of TRAPPIST-1e. Our study highlights various biases of GCMs and emphasizes the importance of not relying solely on one model to understand exoplanet climates.

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D. Sergeev, T. Fauchez, M. Turbet, et. al.
Fri, 24 Sep 21
74/81

Comments: 32 pages, 20 figures; Submitted to the Planetary Science Journal as Part II of a series of 3 THAI papers. Comments on the manuscript are welcome

The young Sun's XUV-activity as a constraint for lower CO$_2$-limits in the Earth's Archean atmosphere [EPA]

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http://arxiv.org/abs/2109.01604


Despite their importance for determining the evolution of the Earth’s atmosphere and surface conditions, the evolutionary histories of the Earth’s atmospheric CO$_2$ abundance during the Archean eon and the Sun’s activity are poorly constrained. In this study, we apply a state-of-the-art physical model for the upper atmosphere of the Archean Earth to study the effects of different atmospheric CO$_2$/N$_2$ mixing ratios and solar activity levels on the escape of the atmosphere to space. We find that unless CO$_2$ was a major constituent of the atmosphere during the Archean eon, enhanced heating of the thermosphere by the Sun’s strong X-ray and ultraviolet radiation would have caused rapid escape to space. We derive lower limits on the atmospheric CO$_2$ abundance of approximately 40\% at 3.8~billion years ago, which is likely enough to counteract the faint young Sun and keep the Earth from being completely frozen. Furthermore, our results indicate that the Sun was most likely born as a slow to moderate {rotating young G-star} to prevent rapid escape, putting essential constraints on the Sun’s activity evolution throughout the solar system’s history. In case that there were yet unknown cooling mechanisms present in the Archean atmosphere, this could reduce our CO$_2$ stability limits, and it would allow a more active Sun.

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C. Johnstone, H. Lammer, K. Kislyakova, et. al.
Mon, 6 Sep 21
17/48

Comments: 40 pages, 6 figures. This is a preprint accepted to be published in Earth and Planetary Science Letters

Low volcanic outgassing rates for a stagnant lid Archean Earth with graphite-saturated magmas [EPA]

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http://arxiv.org/abs/2108.13438


Volcanic gases supplied a large part of Earth’s early atmosphere, but constraints on their flux are scarce. Here we model how C-O-H outgassing could have evolved through the late Hadean and early Archean, under the conditions that global plate tectonics had not yet initiated, all outgassing was subaerial, and graphite was the stable carbon phase in the melt source regions. The model fully couples numerical mantle convection, partitioning of volatiles into the melt, and chemical speciation in the gas phase. The mantle oxidation state (which may not have reached late Archean values in the Hadean) is the dominant control on individual species’ outgassing rates because it affects both the carbon content of basaltic magmas and the speciation of degassed volatiles. Volcanic gas from mantles more reduced than the iron-w\”ustite mineral redox buffer would contain virtually no CO2 because (i) carbonate ions dissolve in magmas only in very limited amounts, and (ii) almost all degassed carbon takes the form of CO instead of CO2. For oxidised mantles near the quartz-fayalite-magnetite buffer, we predict median CO2 outgassing rates of less than approximately 5 Tmol/yr, still lower than the outgassing rates used in many Archean climate studies. Relatively weak outgassing is due in part to the redox-limited CO2 contents of graphite-saturated melts, and also to a stagnant lid regime’s inefficient replenishment of upper mantle volatiles. Our results point to certain chemical and geodynamic prerequisites for sustaining a clement climate with a volcanic greenhouse under the Faint Young Sun.

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C. Guimond, L. Noack, G. Ortenzi, et. al.
Wed, 1 Sep 21
48/53

Comments: 25 pages, 9 figures, accepted for publication in PEPI

Catalog of Gamma-ray Glows during Four Winter Seasons in Japan [CL]

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http://arxiv.org/abs/2108.01829


In 2015 the Gamma-Ray Observation of Winter Thunderstorms (GROWTH) collaboration launched a mapping observation campaign for high-energy atmospheric phenomena related to thunderstorms and lightning discharges. This campaign has developed a detection network of gamma rays with up to 10 radiation monitors installed in Kanazawa and Komatsu cities, Ishikawa Prefecture, Japan, where low-charge-center winter thunderstorms frequently occur. During four winter seasons from October 2016 to April 2020, in total 70 gamma-ray glows, minute-lasting bursts of gamma rays originating from thunderclouds, were detected. Their average duration is 58.9 sec. Among the detected events, 77% were observed in nighttime. The gamma-ray glows can be classified into temporally-symmetric, temporally-asymmetric, and lightning-terminated types based on their count-rate histories. An averaged energy spectrum of the gamma-ray glows is well fitted with a power-law function with an exponential cutoff, whose photon index, cutoff energy, and flux are $0.613\pm0.009$, $4.68\pm0.04$ MeV, and $(1.013\pm0.003)\times10^{-5}$ erg cm$^{-2}$ s$^{-1}$ (0.2-20.0MeV), respectively. The present paper provides the first catalog of gamma-ray glows and their statistical analysis detected during winter thunderstorms in the Kanazawa and Komatsu areas.

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Y. Wada, T. Matsumoto, T. Enoto, et. al.
Thu, 5 Aug 21
30/57

Comments: 33 pages, 31 figures, submitted to Physical Review Research

The emergence of a summer hemisphere jet in planetary atmospheres [EPA]

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http://arxiv.org/abs/2108.00457


Zonal jets are common in planetary atmospheres. Their character, structure, and seasonal variability depend on the planetary parameters. During solstice on Earth and Mars, there is a strong westerly jet in the winter hemisphere and weak, low-level westerlies in the ascending regions of the Hadley cell in the summer hemisphere. This summer jet has been less explored in a broad planetary context, both due to the dominance of the winter jet and since the balances controlling it are more complex, and understanding them requires exploring a broader parameter regime. To better understand the jet characteristics on terrestrial planets and the transition between winter- and summer-dominated jet regimes, we explore the jet’s dependence on rotation rate and obliquity. Across a significant portion of the parameter space, the dominant jet is in the winter hemisphere, and the summer jet is weaker and restricted to the boundary layer. However, we show that for slow rotation rates and high obliquities, the strongest jet is in the summer rather than the winter hemisphere. Analysis of the summer jet’s momentum balance reveals that the balance is not simply cyclostrophic and that both boundary layer drag and vertical advection are essential. At high obliquities and slow rotation rates, the cross-equatorial winter cell is wide and strong. The returning poleward flow in the summer hemisphere is balanced by low-level westerlies through an Ekman balance and momentum is advected upwards close to the ascending branch, resulting in a mid-troposphere summer jet.

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I. Guendelman, D. Waugh and Y. Kaspi
Tue, 3 Aug 21
25/90

Comments: Accepted for publication in the Journal of the Atmospheric Sciences

Beyond runaway: initiation of the post-runaway greenhouse state on rocky exoplanets [EPA]

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http://arxiv.org/abs/2107.14150


The runaway greenhouse represents the ultimate climate catastrophe for rocky, Earth-like worlds: when the incoming stellar flux cannot be balanced by radiation to space, the oceans evaporate and exacerbate heating, turning the planet into a hot wasteland with a steam atmosphere overlying a possibly molten magma surface. The equilibrium state beyond the runaway greenhouse instellation limit depends on the radiative properties of the atmosphere and its temperature structure. Here, we use 1-D radiative-convective models of steam atmospheres to explore the transition from the tropospheric radiation limit to the post-runaway climate state. To facilitate eventual simulations with 3-D global circulation models, a computationally efficient band-grey model is developed, which is capable of reproducing the key features of the more comprehensive calculations. We analyze two factors which determine the equilibrated surface temperature of post-runaway planets. The infrared cooling of the planet is strongly enhanced by the penetration of the dry adiabat into the optically thin upper regions of the atmosphere. In addition, thermal emission of both shortwave and near-IR fluxes from the hot lower atmospheric layers, which can radiate through window regions of the spectrum, is quantified. Astronomical surveys of rocky exoplanets in the runaway greenhouse state may discriminate these features using multi-wavelength observations.

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R. Boukrouche, T. Lichtenberg and R. Pierrehumbert
Fri, 30 Jul 21
25/71

Comments: Accepted for publication in ApJ; 19 pages, 11 figures; Summary video available at this https URL

Sensitivity estimates for diffuse, point-like and extended neutrino sources with KM3NeT/ARCA [IMA]

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http://arxiv.org/abs/2107.13050


The identification of cosmic objects emitting high energy neutrinos could provide new insights about the Universe and its active sources. The existence of these cosmic neutrinos has been proven by the IceCube collaboration, but the big question of which sources these neutrinos originate from, remains unanswered. The KM3NeT detector for Astroparticle Research with Cosmics in the Abyss (ARCA), with a cubic kilometer instrumented volume, is currently being built in the Mediterranean Sea. It will excel at identifying cosmic neutrino sources due to its unprecedented angular resolution for muon neutrinos (< 0.2 degree for E > 10 TeV events). KM3NeT has a view of the sky complementary to IceCube, and is sensitive to neutrinos across a wide range of energies. In order to identify the signature of cosmic neutrino sources in the background of atmospheric neutrinos and muons, statistical methods are being developed and tested with Monte-Carlo pseudo experiments. This contribution presents the most recent sensitivity estimates for diffuse, point-like and extended neutrino sources with KM3NeT/ARCA.

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R. Muller, A. Heijboer, A. Soto, et. al.
Thu, 29 Jul 21
25/59

Comments: 6 pages, 4 figures, VLVNT 2021 conference proceedings

Short term minutes-time scale temporal variation statistics of sodium layer dynamics [IMA]

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http://arxiv.org/abs/2107.13424


The brightness and height of the sodium laser guide star of adaptive optics could vary significantly due to the temporal dynamics of sodium column density and the mean height of sodium layer. To measure these dynamics, an independent sodium Lidar is a necessity. Without such an instrument, it is almost impossible to discern the cause of the brightness variation of laser guide star from the sodium layer’s dynamics or other factors from the laser itself. For applications such as characterizing the performance of sodium laser for sodium laser guide star generation, minutes scale short term statistics of the sodium layers’ abundance and height is extremely helpful for estimating the contribution of sodium layer’s variation to the variation of laser guide star’s brightness. In this paper, we analyzed our previous measurement of sodium layer dynamics that has been gathered in two winters, and presented the temporal variation statistics of sodium column density and mean height within minute time scale based on our measurements.

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L. Feng, K. Jin, H. Li, et. al.
Thu, 29 Jul 21
52/59

Comments: submitted to PASP

The influence of upper boundary conditions on molecular kinetic atmospheric escape simulations [EPA]

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http://arxiv.org/abs/2107.12343


Molecular kinetic simulations are typically used to accurately describe the tenuous regions of the upper atmospheres on planetary bodies. These simulations track the motion of particles representing real atmospheric atoms and/or molecules subject to collisions, the object’s gravity, and external influences. Because particles can end up in very large ballistic orbits, upper boundary conditions (UBC) are typically used to limit the domain size thereby reducing the time for the atmosphere to reach steady-state. In the absence of a clear altitude at which all molecules are removed, such as a Hill sphere, an often used condition is to choose an altitude at which collisions become infrequent so that particles on escape trajectories are removed. The remainder are then either specularly reflected back into the simulation domain or their ballistic trajectories are calculated analytically or explicitly tracked so they eventually re-enter the domain. Here we examine the effect of the choice of the UBC on the escape rate and the structure of the atmosphere near the nominal exobase in the convenient and frequently used 1D spherically symmetric approximation. Using Callisto as the example body, we show that the commonly used specular reflection UBC can lead to significant uncertainties when simulating a species with a lifetime comparable to or longer than a dynamical time scale, such as an overestimation of escape rates and an inflated exosphere. Therefore, although specular reflection is convenient, the molecular lifetimes and body’s dynamical time scales need to be considered even when implementing the convenient 1D spherically symmetric simulations in order to accurately estimate the escape rate and the density and temperature structure in the transition regime.

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S. Mogan, O. Tucker and R. Johnson
Tue, 27 Jul 21
70/97

Comments: N/A

Variations of the Martian Thermospheric Gravity Wave Activity during the Recent Solar Minimum as Observed by MAVEN [EPA]

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http://arxiv.org/abs/2107.09875


Atmospheric gravity (buoyancy) waves (GWs) are of great importance for the energy and momentum budget of all planetary atmospheres. Propagating upward waves carry energy and momentum from the lower atmosphere to thermospheric altitudes and re-distribute them there. On Mars, GWs dominate the variability of the thermosphere and ionosphere. We provide a comprehensive climatology of Martian thermospheric GW activity at solar minimum (end of Solar Cycle 24) inferred from measurements by Neutral Gas and Ions Mass Spectrometer on board Mars Atmosphere and Volatile EvolutioN (NGIMS/MAVEN). The results are compared and interpreted using a one-dimensional spectral nonlinear GW model. Monthly mean GW activity varies strongly as a function of altitude (150-230 km) between 6-25%, reaching a maximum at $\sim$170 km. GW activity systematically exhibits a local time variability with nighttime values exceeding those during daytime, in accordance with previous studies. The analysis suggests that the day-night difference is primarily caused by a competition between dissipation due to molecular diffusion and wave growth due to decreasing background density. Thus, convective instability mechanism is likely to play a less important role in limiting GW amplitudes in the upper thermosphere, which explains their local time behavior.

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E. Yiğit, A. Medvedev and P. Hartogh
Thu, 22 Jul 21
26/59

Comments: Accepted in the Astrophysical Journal

Studying Bioluminescence Flashes with the ANTARES Deep Sea Neutrino Telescope [CL]

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http://arxiv.org/abs/2107.08063


We develop a novel technique to exploit the extensive data sets provided by underwater neutrino telescopes to gain information on bioluminescence in the deep sea. The passive nature of the telescopes gives us the unique opportunity to infer information on bioluminescent organisms without actively interfering with them. We propose a statistical method that allows us to reconstruct the light emission of individual organisms, as well as their location and movement. A mathematical model is built to describe the measurement process of underwater neutrino telescopes and the signal generation of the biological organisms. The Metric Gaussian Variational Inference algorithm is used to reconstruct the model parameters using photon counts recorded by the neutrino detectors. We apply this method to synthetic data sets and data collected by the ANTARES neutrino telescope. The telescope is located 40 km off the French coast and fixed to the sea floor at a depth of 2475 m. The runs with synthetic data reveal that we can reliably model the emitted bioluminescent flashes of the organisms. Furthermore, we find that the spatial resolution of the localization of light sources highly depends on the configuration of the telescope. Precise measurements of the efficiencies of the detectors and the attenuation length of the water are crucial to reconstruct the light emission. Finally, the application to ANTARES data reveals the first precise localizations of bioluminescent organisms using neutrino telescope data.

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N. Reeb, S. Hutschenreuter, P. Zehetner, et. al.
Tue, 20 Jul 21
34/104

Comments: N/A

Impact of Scene-Specific Enhancement Spectra on Matched Filter Greenhouse Gas Retrievals from Imaging Spectroscopy [CL]

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http://arxiv.org/abs/2107.05578


Matched filter (MF) techniques have been widely used for retrieval of greenhouse gas enhancements (enh.) from imaging spectroscopy datasets. While multiple algorithmic techniques and refinements have been proposed, the greenhouse gas target spectrum used for concentration enh. estimation has remained largely unaltered since the introduction of quantitative MF retrievals. The magnitude of retrieved methane and carbon dioxide enh., and thereby integrated mass enh. (IME) and estimated flux of point-source emitters, is heavily dependent on this target spectrum. Current standard use of molecular absorption coefficients to create unit enh. target spectra does not account for absorption by background concentrations of greenhouse gases, solar and sensor geometry, or atmospheric water vapor absorption. We introduce geometric and atmospheric parameters into the generation of scene-specific (SS) unit enh. spectra to provide target spectra that are compatible with all greenhouse gas retrieval MF techniques. For methane plumes, IME resulting from use of standard, generic enh. spectra varied from -22 to +28.7% compared to SS enh. spectra. Due to differences in spectral shape between the generic and SS enh. spectra, differences in methane plume IME were linked to surface spectral characteristics in addition to geometric and atmospheric parameters. IME differences for carbon dioxide plumes, with generic enh. spectra producing integrated mass enh. -76.1 to -48.1% compared to SS enh. spectra. Fluxes calculated from these integrated enh. would vary by the same %s, assuming equivalent wind conditions. Methane and carbon dioxide IME were most sensitive to changes in solar zenith angle and ground elevation. SS target spectra can improve confidence in greenhouse gas retrievals and flux estimates across collections of scenes with diverse geometric and atmospheric conditions.

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M. Foote, P. Dennison, P. Sullivan, et. al.
Tue, 13 Jul 21
43/79

Comments: 14 pages, 5 figures, 3 tables

Could macroscopic dark matter (macros) give rise to mini-lightning flashes out of a blue sky without clouds? [CL]

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http://arxiv.org/abs/2107.05338


A recent study pointed out that macroscopic dark matter (macros) traversing through the earth’s atmosphere can give rise to hot and ionized channels similar to those associated with lightning leaders. The authors of the study investigated the possibility that when such channels created by macros pass through a thundercloud, lightning leaders may locked into these ionized channels creating lightning discharges with perfectly straight channels. They suggested the possibility of detecting such channels as a means of detecting the passage of macros through the atmosphere. In this paper, we show that macros crossing the atmosphere under fair weather conditions could also give rise to mini lightning flashes with current amplitudes in the order of few hundreds of Amperes. These mini lightning flashes would generate a thunder signature similar to or stronger than those of long laboratory sparks and they could also be detected by optical means. As in the case of thunderstorm assisted macro lightning, these mini-lightning flashes are also associated with straight channels. Moreover, since the frequency of mini lightning flashes are about a thousand times more frequent than the macro generated lightning flashes which were assisted by thunderstorms, they could be used as a means to look for the paths of macroscopic dark matter crossing the atmosphere.

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V. Cooray, G. Cooray, M. Rubinstein, et. al.
Tue, 13 Jul 21
47/79

Comments: N/A

Polarimetric Signature of Ocean as Detected by Near-Infrared Earthshine Observations [EPA]

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http://arxiv.org/abs/2106.10099


Context. The discovery of an extrasolar planet with an ocean has crucial importance in the search for life beyond Earth. The polarimetric detection of specularly reflected light from a smooth liquid surface is anticipated theoretically, though the polarimetric signature of Earth’s ocean has not yet been conclusively detected in disk-integrated planetary light. Aims. We aim to detect and measure the polarimetric signature of the Earth’s ocean. Methods. We conducted near-infrared polarimetry for lunar Earthshine and collected data for 32 nights with a variety of ocean fractions in the Earthshine contributing region. Results. A clear positive correlation was revealed between the polarization degree and ocean fraction. We found hourly variations in polarization in accordance with rotational transition of the ocean fraction. The ratios of the variation to the typical polarization degree were as large as ~0.2-1.4. Conclusions. Our observations provide plausible evidence of the polarimetric signature attributed to Earth’s ocean. Near-infrared polarimetry may be considered a prospective technique for the search for exoplanetary oceans.

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J. Takahashi, Y. Itoh, T. Matsuo, et. al.
Mon, 21 Jun 21
20/54

Comments: Accepted for publication in A&A (21 pages, 13 figures, 3 tables)

Photodetachment and Test-Particle Simulation Constraints on Negative Ions in Solar System Plasmas [CL]

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http://arxiv.org/abs/2106.08764


Negative ions have been detected in abundance in recent years by spacecraft across the solar system. These detections were, however, made by instruments not designed for this purpose and, as such, significant uncertainties remain regarding the prevalence of these unexpected plasma components. In this article, the phenomenon of photodetachment is examined and experimentally and theoretically derived cross-sections are used to calculate photodetachment rates for a range of atomic and molecular negative ions subjected to the solar photon spectrum. These rates are applied to negative ions outflowing from Europa, Enceladus, Titan, Dione and Rhea and their trajectories are traced to constrain source production rates and the extent to which negative ions are able to pervade the surrounding space environments. Predictions are also made for further negative ion populations in the outer solar system with Triton used as an illustrative example. This study demonstrates how, at increased heliocentric distances, negative ions can form stable ambient plasma populations and can be exploited by future missions to the outer solar system.

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R. Desai, Z. Zhang, X. Wu, et. al.
Thu, 17 Jun 21
63/74

Comments: Planetary Science Journal Article, accepted 05 April 2021. Preprint contains 21 pages, 8 figures, 1 table

Role of Surface Gravity Waves in Aquaplanet Ocean Climates [CL]

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http://arxiv.org/abs/2106.05032


We present a set of idealised numerical experiments of a solstitial aquaplanet ocean and examine the thermodynamic and dynamic implications of surface gravity waves (SGWs) upon its mean state. The aquaplanet’s oceanic circulation is dominated by an equatorial zonal jet and four Ekman driven meridional overturning circulation (MOC) cells aligned with the westerly atmospheric jet streams and easterly trade winds in both hemispheres. Including SGW parameterization (representing modulations of air-sea momentum fluxes, Langmuir circulation and Stokes-Coriolis force) increases mixed layer vertical momentum diffusivity by approx. 40% and dampens surface momentum fluxes by approx. 4%. The correspondingly dampened MOC impacts the oceanic density structure to 1 km depth by lessening the large-scale advective transports of heat and salt, freshening the equatorial latitudes (where evaporation minus precipitation [E-P] is negative) and increasing salinity in the subtropics (where E-P is positive) by approx. 1%. The midlatitude pycnocline in both hemispheres is deepened by the inclusion of SGWs. Including SGWs into the aquaplanet ocean model acts to increase mixed layer depth by approx. 10% (up to 20% in the wintertime in midlatitudes), decrease vertical shear in the upper 200 m and alter local midlatitude buoyancy frequency. Generally, the impacts of SGWs upon the aquaplanet ocean are found to be consistent across cooler and warmer climates. We suggest that the implications of these simulations could be relevant to understanding future projections of SGW climate, exoplanetary oceans, and the dynamics of the Southern Ocean mixed layer.

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J. Studholme, M. Markina and S. Gulev
Thu, 10 Jun 21
38/77

Comments: N/A

A generalized approach to compensate for low and high frequency errors in FFT based phase screen simulations [IMA]

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http://arxiv.org/abs/2106.01002


Fast Fourier Transform based phase screen simulations give accurate results only when the screen size ($G$) is much larger than the outer scale parameter ($L_0$). Otherwise, they fall short in correctly predicting both the low and high frequency behaviours of turbulence induced phase distortions. Sub-harmonic compensation is a commonly used technique that aids in low-frequency correction but does not solve the problem for all values of screen size to outer scale parameter ratios $(G/L_0$). A subharmonics based approach will lead to unequal sampling or weights calculation for subharmonics addition at the low-frequency range and patch normalization factor. We have modified the subharmonics based approach by introducing a Gaussian phase autocorrelation matrix that compensates for these shortfalls. We show that the maximum relative error in structure function with respect to theoretical value is as small as 0.5-3% for $(G/L_0$) ratio of 1/1000 even for screen sizes up to 100 m diameter.

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S. Chhabra, J. Paul, A. Ramaprakash, et. al.
Thu, 3 Jun 21
7/55

Comments: 23 pages, 12 figures, 1 table, Accepted for Publication in JATIS (SPIE)

Electric quadrupole transitions in carbon dioxide [CL]

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http://arxiv.org/abs/2106.00585


Recent advances in the high sensitivity spectroscopy have made it possible, in combination with accurate theoretical predictions, to observe for the first time very weak electric quadrupole transitions in a polar polyatomic molecule of water. Here we present accurate theoretical predictions of the complete quadrupole ro-vibrational spectrum of a non-polar molecule CO$_2$, important in atmospheric and astrophysical applications. Our predictions are validated by recent cavity enhanced absorption spectroscopy measurements and are used to assign few weak features in the recent ExoMars ACS MIR spectroscopic observations of the martian atmosphere. Predicted quadrupole transitions appear in some of the mid-infrared CO$_2$ and water vapor transparency regions, making them important for detection and characterization of the minor absorbers in water- and CO$_2$-rich environments, such as present in the atmospheres of Earth, Venus and Mars.

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A. Yachmenev, A. Campargue, S. Yurchenko, et. al.
Wed, 2 Jun 21
5/48

Comments: N/A

Charge injection into the atmosphere by explosive volcanic eruptions [CL]

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http://arxiv.org/abs/2105.14400


Volcanic eruptions are associated with a wide range of electrostatic effects. Increasing evidence suggests that high-altitude discharges (lightning) in maturing plumes are driven by electrification processes that require the formation of ice (analogous to processes underpinning meteorological thunderstorms). However, electrical discharges are also common at or near the volcanic vent. A number of “ice-free” electrification mechanisms have been proposed to account for this activity: fractocharging, triboelectric charging, radioactive charging, and charging through induction. Yet, the degree to which each mechanism contributes to a jet’s total electrification and how electrification in the gas-thrust region influences electrostatic processes aloft remains poorly constrained. Here, we use a shock-tube to simulate overpressured volcanic jets capable of producing spark discharges in the absence of ice. These discharges may be representative of the continual radio frequency (CRF) emissions observed at a number of eruptions. Using a suite of electrostatic sensors, we demonstrate the presence of size-dependent bipolar charging (SDBC) in a discharge-bearing flow for the first time. SDBC has been readily associated with triboelectric charging in other contexts and provides direct evidence that contact and frictional electrification play significant roles in electrostatic processes in the vent and near-vent regions of an eruption. Additionally, we find that particles leaving the region where discharges occur remain moderately electrified. This degree of electrification may be sufficient to drive near-vent lightning higher in the column. Thus, near-vent discharges may be underpinned by the same electrification mechanisms driving CRF, albeit involving greater degrees of charge separation.

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J. Harper, C. Cimarelli, V. Cigala, et. al.
Tue, 1 Jun 21
14/72

Comments: N/A

Restoring the top-of-atmosphere reflectance during solar eclipses: a proof of concept with the UV Absorbing Aerosol Index measured by TROPOMI [CL]

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http://arxiv.org/abs/2105.13311


During a solar eclipse the solar irradiance reaching the top-of-atmosphere (TOA) is reduced in the Moon shadow. The solar irradiance is commonly measured by Earth observation satellites before the start of the solar eclipse and is not corrected for this reduction, which results in a decrease of the computed TOA reflectances. Consequently, air quality products that are derived from TOA reflectance spectra, such as the ultraviolet (UV) Absorbing Aerosol Index (AAI), are distorted or undefined in the shadow of the Moon. The availability of air quality satellite data in the penumbral and antumbral shadow during solar eclipses, however, is of particular interest to users studying the atmospheric response to solar eclipses. Given the time and location of a point on the Earth’s surface, we explain how to compute the obscuration during a solar eclipse taking into account wavelength-dependent solar limb darkening. With the calculated obscuration fractions, we restore the TOA reflectances and the AAI in the penumbral shadow during the annular solar eclipses on 26 December 2019 and 21 June 2020 measured by the TROPOMI/S5P instrument. In the corrected products, the signature of the Moon shadow disappeared, but only if wavelength-dependent solar limb darkening is taken into account. We conclude that the correction method of this paper can be used to detect real AAI rising phenomena during a solar eclipse and has the potential to restore any other product that is derived from TOA reflectance spectra. This would resolve the solar eclipse anomalies in satellite air quality measurements and would allow for studying the effect of the eclipse obscuration on the composition of the Earth’s atmosphere from space.

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V. Trees, P. Wang and P. Stammes
Fri, 28 May 21
51/56

Comments: Accepted for publication in Atmospheric Chemistry and Physics

How much has the Sun influenced Northern Hemisphere temperature trends? An ongoing debate [CL]

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http://arxiv.org/abs/2105.12126


To evaluate the role of Total Solar Irradiance (TSI) on Northern Hemisphere (NH) surface air temperature trends it is important to have reliable estimates of both quantities. 16 different TSI estimates were compiled from the literature. 1/2 of these estimates are low variability and 1/2 are high variability. 5 largely-independent methods for estimating NH temperature trends were evaluated using: 1) only rural weather stations; 2) all available stations whether urban or rural (the standard approach); 3) only sea surface temperatures; 4) tree-ring temperature proxies; 5) glacier length temperature proxies. The standard estimates using urban as well as rural stations were anomalous as they implied a much greater warming in recent decades than the other estimates. This suggests urbanization bias might still be a problem in current global temperature datasets despite the conclusions of some earlier studies. Still, all 5 estimates confirm it is currently warmer than the late 19th century, i.e., there has been some global warming since 1850. For the 5 estimates of NH temperatures, the contribution from direct solar forcing for all 16 estimates of TSI was evaluated using simple linear least-squares fitting. The role of human activity in recent warming was then calculated by fitting the residuals to the UN IPCC’s recommended anthropogenic forcings time series. For all 5 NH temperature series, different TSI estimates implied everything from recent global warming being mostly human-caused to it being mostly natural. It seems previous studies (including the most recent IPCC reports) that had prematurely concluded the former failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with NH temperature trend estimates. Several recommendations are provided on how future research could more satisfactorily resolve these issues.

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R. Connolly, W. Soon, M. Connolly, et. al.
Thu, 27 May 21
43/62

Comments: 71 pages, 18 figures. To be published in Research in Astronomy and Astrophysics

Redox hysteresis of super-Earth exoplanets from magma ocean circulation [EPA]

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http://arxiv.org/abs/2105.11208


Internal redox reactions may irreversibly alter the mantle composition and volatile inventory of terrestrial and super-Earth exoplanets and affect the prospects for atmospheric observations. The global efficacy of these mechanisms, however, hinges on the transfer of reduced iron from the molten silicate mantle to the metal core. Scaling analysis indicates that turbulent diffusion in the internal magma oceans of sub-Neptunes can kinetically entrain liquid iron droplets and quench core formation. This suggests that the chemical equilibration between core, mantle, and atmosphere may be energetically limited by convective overturn in the magma flow. Hence, molten super-Earths possibly retain a compositional memory of their accretion path. Redox control by magma ocean circulation is positively correlated with planetary heat flow, internal gravity, and planet size. The presence and speciation of remanent atmospheres, surface mineralogy, and core mass fraction of atmosphere-stripped exoplanets may thus constrain magma ocean dynamics.

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T. Lichtenberg
Tue, 25 May 21
41/75

Comments: Accepted for publication in ApJL; 7 pages, 2 figures; summaries available at this http URL (blog) and this http URL (video)

Axion Quark Nuggets. Dark Matter and Matter-Antimatter asymmetry: theory, observations and future experiments [CL]

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http://arxiv.org/abs/2105.08719


We review a testable, the axion quark nugget (AQN) model outside of the standard WIMP paradigm. The model was originally invented to explain the observed similarity between the dark and the visible components, $\Omega_{\rm DM}\approx \Omega_{\rm visible}$ in a natural way as both types of matter are formed during the same QCD transition and proportional to the same dimensional fundamental parameter of the system, $\Lambda_{\rm QCD}$. In this framework the baryogenesis is actually a charge segregation (rather than charge generation) process which is operational due to the $\cal{CP}$-odd axion field,while the global baryon number of the Universe remains zero. The nuggets and anti-nuggets are strongly interacting but macroscopically large objects with approximately nuclear density. We overview several specific recent applications of this framework. First, we discuss the “solar corona mystery” when the so-called nanoflares are identified with the AQN annihilation events in corona. Secondly, we review a proposal that the recently observed by the Telescope Array puzzling events is a result of the annihilation events of the AQNs under thunderstorm. Finally, we overview a broadband strategy which could lead to the discovery the AQN-induced axions representing the heart of the construction.

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A. Zhitnitsky
Wed, 19 May 21
22/64

Comments: invited brief review to be published in MPLA

Temporal changes of near-surface air temperature in Poland for 1781-2016 and in Tbilisi (Georgia) for 1881-2016 [CL]

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http://arxiv.org/abs/2105.06389


Analyses of near-surface air temperature T in Poland for 1781-2016 and in Tbilisi (Georgia) for 1881-2016 have been carried out. We show that the centenary warming effect in Poland and in Tbilisi has almost the same peculiarities. An average centenary warming effect deltaT = (1.08+/-0.29) C is observed in Poland and in Tbilisi for 1881-2016. A warming effect is larger in winter season (deltaT = ~1.15 C) than in other seasons (average warming effect for these seasons deltaT = ~0.95 C). We show that a centenary warming is mainly related to the change of solar activity (estimated by sunspot numbers (SSN) and total solar irradiance (TSI)); particularly, a time interval about ~70 years (1890-1960), when a correlation coefficients between 11 years smoothed SSN and T, and TSI and T are high, r = 0.66+/-0.07 and r = 0.73+/-0.07 for Poland and r = 0.82+/-0.05 and r = 0.90+/-0.05 for Tbilisi, respectively; in this period solar activity contributes decisively in the global warming. We show that a global warming effect equals zero based on the temperature T data in Poland for period 1781-1880, when human activities were relatively less than in 1881-2016. We recognize a few feeble ~20+/-3 years disturbances in the temperature changes for period 1885-1980, most likely related with the fluctuations of solar magnetic cycles. We distinguish the fluctuations of ~7-8 years in Poland’s T data, possibly connected with local effects of the North Atlantic Oscillation.

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R. Modzelewska, M. Alania, N. Kapanadze, et. al.
Fri, 14 May 21
3/67

Comments: 12 pages, 6 figures

Trajectories of long duration balloons launched from McMurdo Station in Antarctica [CL]

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http://arxiv.org/abs/2105.04173


The Columbia Scientific Ballooning Facility operates stratospheric balloon flights out of McMurdo Station in Antarctica. We use balloon trajectory data from 40 flights between 1991 and 2016 to give the first quantification of trajectory statistics. We provide the probabilities as a function of time for the payload to be between given latitudes, and we quantify the southernmost and northernmost latitudes a payload is likely to attain. We find that for the median flight duration of 19 days, there is 90% probability the balloon would drift as far south as $88^{\circ}$S or as far north as $71^{\circ}$S; shorter flights are likely to experience smaller ranges in latitude. These statistics, which are available digitally in the public domain, will enable scientists planning future balloon flights make informed decisions during both mission design and execution.

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C. Geach, S. Hanany, C. Tan, et. al.
Tue, 11 May 21
87/93

Comments: 7 pages, 8 figures

Low-level jets and the convergence of Mars data assimilation algorithms [EPA]

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http://arxiv.org/abs/2105.03283


Data assimilation is an increasingly popular technique in Mars atmospheric science, but its effect on the mean states of the underlying atmosphere models has not been thoroughly examined. The robustness of results to the choice of model and assimilation algorithm also warrants further study. We investigate these issues using two Mars general circulation models (MGCMs), with particular emphasis on zonal wind and temperature fields. When temperature retrievals from the Mars Global Surveyor Thermal Emission Spectrometer (TES) are assimilated into the U.K.-Laboratoire de M\’et\’eorologie Dynamique (UK-LMD) MGCM to create the Mars Analysis Correction Data Assimilation (MACDA) reanalysis, low-level zonal jets in the winter northern hemisphere shift equatorward and weaken relative to a free-running control simulation from the same MGCM. The Ensemble Mars Atmosphere Reanalysis System (EMARS) reanalysis, which is also based on TES temperature retrievals, also shows jet weakening (but less if any shifting) relative to a control simulation performed with the underlying Geophysical Fluid Dynamics Laboratory (GFDL) MGCM. Examining higher levels of the atmosphere, monthly mean three-dimensional temperature and zonal wind fields are in generally better agreement between the two reanalyses than between the two control simulations. In conjunction with information about the MGCMs’ physical parametrizations, intercomparisons between the various reanalyses and control simulations suggest that overall the EMARS control run is plausibly less biased (relative to the true state of the Martian atmosphere) than the MACDA control run. Implications for future observational studies are discussed.

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T. Mooring, G. Davis and S. Greybush
Mon, 10 May 21
15/60

Comments: 25 pages, 6 figures

The traditional approximation of rotation for rapidly rotating stars and planets. I. The impact of strong deformation [SSA]

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http://arxiv.org/abs/2104.09302


The Traditional Approximation of Rotation (TAR) is a treatment of the hydrodynamic equations of rotating and stably stratified fluids in which the action of the Coriolis acceleration along the direction of the entropy and chemical stratifications is neglected because it is weak in comparison with the buoyancy force. The dependent variables in the equations for the dynamics of gravito-inertial waves (GIWs) then become separable into radial and horizontal parts as in the non-rotating case. The TAR is built on the assumptions that the star is spherical (i.e. its centrifugal deformation is neglected) and uniformly rotating. We study the feasibility of carrying out a generalisation of the TAR to account for the centrifugal acceleration in the case of strongly deformed uniformly and rapidly rotating stars (and planets), and to identify the validity domain of this approximation. We built analytically a complete formalism that allows the study of the dynamics of GIWs in spheroidal coordinates which take into account the flattening of rapidly rotating stars by assuming the hierarchies of frequencies adopted within the TAR in the spherical case and by deriving a generalised Laplace tidal equation for the horizontal eigenfunctions of the GIWs and their asymptotic wave periods, which can be used to probe the structure and dynamics of rotating deformed stars with asteroseismology. Using 2D ESTER stellar models, we determine the validity domain of the generalised TAR as a function of the rotation rate of the star normalised by its critical angular velocity and its pseudo-radius. This generalisation allows us to study the signature of the centrifugal effects on GIWs in rapidly rotating deformed stars. We found that the effects of the centrifugal acceleration in rapidly rotating early-type stars on GIWs are theoretically detectable in modern space photometry using observations from Kepler.

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H. Dhouib, V. Prat, T. Reeth, et. al.
Tue, 20 Apr 2021
9/72

Comments: 17 pages, 14 figures, 1 table, abstract shortened for arXiv. Submitted to A&A

Reducing Surface Wetness Leads to Tropical Hydrological Cycle Regime Transition [CL]

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http://arxiv.org/abs/2104.06995


Earth’s modern climate is characterized by wet, rainy deep tropics, however paleoclimate and planetary science have revealed a wide range of hydrological cycle regimes connected to different external parameters. Here we investigate how surface wetness affects the tropical hydrological cycle. When surface wetness is decreased in an Earth-like general circulation model, the tropics remain wet but transition from a rainy to rain-free regime. The rain-free regime occurs when surface precipitation is suppressed as negative evaporation (surface condensation) balances moisture flux convergence. The regime transition is dominated by near-surface relative humidity changes in contrast to the hypothesis that relative humidity changes are small. We show near-surface relative humidity changes responsible for the regime transition are controlled by re-evaporation of stratiform precipitation near the lifting condensation level. Re-evaporation impacts the near-surface through vertical mixing. Our results reveal a new rain-free tropical hydrological cycle regime that goes beyond the wet/dry paradigm.

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B. Fan, Z. Tan, T. Shaw, et. al.
Thu, 15 Apr 2021
40/59

Comments: 9 pages, 4 figures, accepted by Geophysical Research Letters

How does salinity shape ocean circulation and ice geometry on Enceladus and other icy satellites? [EPA]

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http://arxiv.org/abs/2104.07008


Of profound astrobiological interest is that not only does Enceladus have a water ocean, but it also appears to be salty, important for its likely habitability. Here, we investigate how salinity affects ocean dynamics and equilibrium ice shell geometry and use knowledge of ice shell geometry and tidal heating rates to help constrain ocean salinity. We show that the vertical overturning circulation of the ocean, driven from above by melting and freezing and the temperature dependence of the freezing point of water on pressure, has opposing signs at very low and very high salinities. In both cases, heat and freshwater converges toward the equator, where the ice is thick, acting to homogenize thickness variations. In order to maintain observed ice thickness variations, ocean heat convergence should not overwhelm heat loss rates through the equatorial ice sheet. This can only happen when the ocean’s salinity has intermediate values, order $20$~psu. In this case polar-sinking driven by meridional temperature variations is largely canceled by equatorial-sinking circulation driven by salinity variations and a consistent ocean circulation, ice shell geometry and tidal heating rate can be achieved.

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W. Kang, T. Mittal, S. Bire, et. al.
Thu, 15 Apr 2021
47/59

Comments: N/A

The roles of latent heating and dust in the structure and variability of the northern Martian polar vortex [EPA]

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http://arxiv.org/abs/2104.00503


The winter polar vortices on Mars are annular in terms of their potential vorticity (PV) structure, a phenomenon identified in observations, reanalysis and some numerical simulations. Some recent modeling studies have proposed that condensation of atmospheric carbon dioxide at the winter pole is a contributing factor to maintaining the annulus through the release of latent heat. Dust and topographic forcing are also known to be causes of internal and interannual variability in the polar vortices. However, coupling between these factors remains uncertain, and previous studies of their impact on vortex structure and variability have been largely limited to a single Martian global climate model (MGCM). Here, by further developing a novel MGCM, we decompose the relative roles of latent heat and dust as drivers for the variability and structure of the northern Martian polar vortex. We also consider how Martian topography modifies the driving response. By also analyzing a reanalysis dataset we show that there is significant dependence in the polar vortex structure and variability on the observations assimilated. In both model and reanalysis, high atmospheric dust loading (such as that seen during a global dust storm) can disrupt the vortex, cause the destruction of PV in the low-mid altitudes (> 0.1 hPa), and significantly reduce spatial and temporal vortex variability. Through our simulations, we find that the combination of dust and topography primarily drives the eddy activity throughout the Martian year, and that although latent heat release can produce an annular vortex, it has a relatively minor effect on vortex variability.

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E. Ball, D. Mitchell, W. Seviour, et. al.
Fri, 2 Apr 2021
47/55

Comments: 25 pages, 13 figures, submitted to The Planetary Science Journal

Validation of SSUSI derived ionization rates and electron densities [CL]

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http://arxiv.org/abs/2103.08254


The coupling of the atmosphere to the space environment has become recognized as an important driver of atmospheric chemistry and dynamics. In order to quantify the effects of particle precipitation on the atmosphere, reliable global energy inputs on spatial scales commensurate with particle precipitation variations are required. To that end, we have validated the Special Sensor Ultraviolet Spectrographic Imagers (SSUSI) products for average electron energy and electron energy flux by comparing to EISCAT electron density profiles. This comparison shows that SSUSI FUV observations can be used to provide ionization rate profiles throughout the auroral region. The SSUSI on board the Defense Meteorological Satellite Program (DMSP) Block 5D3 satellites provide nearly hourly, high-resolution UV snapshots of auroral emissions. Here we use the SSUSI-derived energies and fluxes to drive standard parametrizations in order to obtain ionization-rate and electron-density profiles in the E-region (90–150 km), which are then compared to EISCAT ground-based electron density measurements. We compare the data from two satellites, DMSP F17 and F18, to the Troms{\o} UHF radar profiles. We find that differentiating between the magnetic local time (MLT) morning (3–11 h) and evening (15–23 h) provides the best fit to the ground-based data. The data agree well in the MLT morning sector using a Maxwellian electron spectrum, while in the evening sector using a Gaussian spectrum and accounting for bounce-electrons achieved optimum agreement with EISCAT. Depending on the satellite and MLT, the median of the differences varies between 0 and 20% above 105 km (F17) and $\pm$15% above 100 km (F18). Because of the large gradient below those altitudes, the relative differences get larger without substantially increasing absolute differences, with virtually no statistically significant differences at the 1-sigma level.

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S. Bender, P. Espy and L. Paxton
Tue, 16 Mar 21
14/92

Comments: 15 pages, 5 figures, in review for Ann. Geophys

A coupled model of episodic warming, oxidation and geochemical transitions on early Mars [EPA]

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http://arxiv.org/abs/2103.06736


Reconciling the geology of Mars with models of atmospheric evolution remains a major challenge. Martian geology is characterized by past evidence for episodic surface liquid water, and geochemistry indicating a slow and intermittent transition from wetter to drier and more oxidizing surface conditions. Here we present a new model incorporating randomized injection of reducing greenhouse gases and oxidation due to hydrogen escape, to investigate the conditions responsible for these diverse observations. We find that Mars could have transitioned repeatedly from reducing (H2-rich) to oxidizing (O2-rich) atmospheric conditions in its early history. Our model predicts a generally cold early Mars, with mean annual temperatures below 240 K. If peak reducing gas release rates and background CO2 levels are high enough, it nonetheless exhibits episodic warm intervals sufficient to degrade crater walls, form valley networks and create other fluvial/lacustrine features. Our model also predicts transient buildup of atmospheric O2, which can help explain the occurrence of oxidized mineral species such as manganese oxides at Gale Crater. We suggest that the apparent Noachian–Hesperian transition from phyllosilicate deposition to sulfate deposition around 3.5 billion years ago can be explained as a combined outcome of increasing planetary oxidation, decreasing groundwater availability and a waning bolide impactor flux, which dramatically slowed the remobilization and thermochemical destruction of surface sulfates. Ultimately, rapid and repeated variations in Mars’ early climate and surface chemistry would have presented both challenges and opportunities for any emergent microbial life.

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R. Wordsworth, A. Knoll, J. Hurowitz, et. al.
Fri, 12 Mar 21
53/59

Comments: Published March 8 2021 in Nature Geoscience

PSFs for mapping artificial night sky luminance over large territories [IMA]

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http://arxiv.org/abs/2103.03341


Knowledge of the night sky radiance over a large territory may be valuable informationto identify sites appropriate to astronomical observations or for assessing the impacts ofartificial light at night on ecosystems. Measuring the sky radiance can be a complex endeavourdepending on the desired temporal and spatial resolution. Similarly, modelling of artificialnight sky radiance for multiple points of a territory can represent a significant amount ofcomputing time depending on the complexity of the model used. The use of the convolutionof a point spread function with the light sources geographical distribution has been suggestedin order to model the sky radiance over large territories of hundreds of kilometres in size.We determine how the point spread function is sensitive to the main driving parameters ofthe artificial night sky radiance such as the wavelength, the ground reflectance, the obstaclesproperties, the Upward Light Output Ratio and the Aerosol Optical Depth using the Illuminav2 model. The obtained functions were used to model the artificial night sky brightness ofthe Mont-M\’egantic International Dark Sky Reserve for winter and summer conditions. Theresults were compared to the New world atlas of artificial night sky brightness, the Illuminav2 model and in situ Sky Quality Camera measurements. We found that the New world atlasoverestimates the artificial sky brightness by 55% whereas the Illumina model underestimatesit by 48%. This may be due to varying atmospherical conditions and the fact that the modelonly accounts for public light sources.

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A. Simoneau, M. Aubé, J. Leblanc, et. al.
Mon, 8 Mar 21
24/65

Comments: N/A

The future lifespan of Earth's oxygenated Atmosphere [EPA]

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http://arxiv.org/abs/2103.02694


Earth’s modern atmosphere is highly oxygenated and is a remotely detectable signal of its surface biosphere. However, the lifespan of oxygen-based biosignatures in Earth’s atmosphere remains uncertain, particularly for the distant future. Here we use a combined biogeochemistry and climate model to examine the likely timescale of oxygen-rich atmospheric conditions on Earth. Using a stochastic approach, we find that the mean future lifespan of Earth’s atmosphere with oxygen levels more than 1% of the present atmospheric level is 1.08+-0.14 billion years. The model projects that a deoxygenation of the atmosphere, with atmospheric oxygen dropping sharply to levels reminiscnet of the Archaean Earth, will most probably be triggered before the inception of moist greenhouse conditions in Earth’s climate system and before the extensive loss of surface water from the atmosphere. We find that future deoxygenation is an inevitable consequence of increasing solar fluxes, whereas its precise timing is modulated by the exchange flux of reducing power between the mantle and the ocean-atmosphere-crust system. Our results suggest that the planetary carbonate-silicate cycle will tend to lead to terminally CO2-limited biospheres and rapid atmospheric deoxygenation, emphasizing the need for robust atmospheric biosignatures applicable to weakly oxygenated and anoxic exoplanet atmospheres and highlighting the potential importance of atmospheric organic haze during the terminal stages of planetary habitability.

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K. Ozaki and C. Reinhard
Fri, 5 Mar 21
49/64

Comments: Manuscript currently in press in Nature Geoscience

Closed-formed ab initio solutions of geometric albedos and reflected light phase curves of exoplanets [EPA]

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http://arxiv.org/abs/2103.02673


The albedo of a celestial body is the fraction of light reflected by it. Studying the albedos of the planets and moons of the Solar System dates back at least a century. Modern astronomical facilities enable the measurement of geometric albedos from visible/optical secondary eclipses and the inference of the Bond albedo (spherical albedo measured over all wavelengths, weighted by the incident stellar flux) from infrared phase curves of transiting exoplanets. Determining the relationship between the geometric and spherical albedos usually involves complex numerical calculations and closed-form solutions are restricted to simple reflection laws. Here we report the discovery of closed-form solutions for the geometric albedo and integral phase function, which apply to any law of reflection that only depends on the scattering angle. The shape of a reflected light phase curve (quantified by the integral phase function) and the secondary eclipse depth (quantified by the geometric albedo) may now be self-consistently inverted to retrieve fundamental physical parameters. Fully-Bayesian phase curve inversions for reflectance maps and simultaneous light curve detrending may now be performed, without the need for binning in time, due to the efficiency of computation. Demonstrating these innovations for the hot Jupiter Kepler-7b, we infer a geometric albedo of $0.19 \pm 0.01$, a Bond albedo of $0.35 \pm 0.03$, a phase integral of $1.84 \pm 0.09$ and a scattering asymmetry factor of $0.18 \pm 0.17$. These ab initio, closed-form solutions enable cloud/haze properties to be retrieved from multi-wavelength phase curves of both gas-giant and terrestrial exoplanets measured by the James Webb Space Telescope.

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K. Heng, B. Morris and D. Kitzmann
Fri, 5 Mar 21
51/64

Comments: 14 pages, 6 figures, 2 tables

The Future Of The Arecibo Observatory: The Next Generation Arecibo Telescope [IMA]

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http://arxiv.org/abs/2103.01367


The Arecibo Observatory (AO) is a multidisciplinary research and education facility that is recognized worldwide as a leading facility in astronomy, planetary, and atmospheric and space sciences. AO’s cornerstone research instrument was the 305-m William E. Gordon telescope. On December 1, 2020, the 305-m telescope collapsed and was irreparably damaged. In the three weeks following the collapse, AO’s scientific and engineering staff and the AO users community initiated extensive discussions on the future of the observatory. The community is in overwhelming agreement that there is a need to build an enhanced, next-generation radar-radio telescope at the AO site. From these discussions, we established the set of science requirements the new facility should enable. These requirements can be summarized briefly as: 5 MW of continuous wave transmitter power at 2 – 6 GHz, 10 MW of peak transmitter power at 430 MHz (also at 220MHz under consideration), zenith angle coverage 0 to 48 deg, frequency coverage 0.2 to 30 GHz and increased FoV. These requirements determine the unique specifications of the proposed new instrument. The telescope design concept we suggest consists of a compact array of fixed dishes on a tiltable, plate-like structure with a collecting area equivalent to a 300m dish. This concept, referred to as the Next Generation Arecibo Telescope (NGAT), meets all of the desired specifications and provides significant new science capabilities to all three research groups at AO. This whitepaper presents a sample of the wide variety of the science that can be achieved with the NGAT, the details of the telescope design concept and the need for the new telescope to be located at the AO site. We also discuss other AO science activities that interlock with the NGAT in the white paper.

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D. Roshi, N. Aponte, E. Araya, et. al.
Wed, 3 Mar 21
60/82

Comments: 82 pages (executive summary 10 pages), 21 figures, Arecibo observatory white paper

New Astronomical, Meteorological and Geological Study of Montefiascone (VT) [IMA]

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http://arxiv.org/abs/2102.12334


In this work that continues the “NGICS – New Italian City Geological Study” a project of the Department of Climatology and Geology of TS Corporation Srl, we present the study relating to the Municipality of Montefiascone (VT). We analyzed 25 years of astronomical, geological, meteorological and climatic data, comparing them to verify the long-term trend of local variations in temperatures, detections, solar radiation and geological events, with the ultimate goal of understanding climate and geological changes a long term in this geographical area. The analysis is performed using a statistical approach and attention is used to minimize any effects caused by the error in case of lack of data.

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D. D.Tasselli, S. S.Ricci and P. P.Bianchi
Thu, 25 Feb 21
36/50

Comments: 36 pages, 22 figures, 8 tables. arXiv admin note: text overlap with arXiv:1910.06101

The rotational and divergent components of atmospheric circulation on tidally locked planets [EPA]

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http://arxiv.org/abs/2102.11760


Tidally locked exoplanets likely host global atmospheric circulations with a superrotating equatorial jet, planetary-scale stationary waves and thermally-driven overturning circulation. In this work, we show that each of these features can be separated from the total circulation by using a Helmholtz decomposition, which splits the circulation into rotational (divergence free) and divergent (vorticity free) components. This technique is applied to the simulated circulation of a terrestrial planet and a gaseous hot Jupiter. For both planets, the rotational component comprises the equatorial jet and stationary waves, and the divergent component contains the overturning circulation. Separating out each component allows us to evaluate their spatial structure and relative contribution to the total flow. In contrast with previous work, we show that divergent velocities are not negligible when compared with rotational velocities, and that divergent, overturning circulation takes the form of a single, roughly isotropic cell that ascends on the day-side and descends on the night-side. These conclusions are drawn for both the terrestrial case and the hot Jupiter. To illustrate the utility of the Helmholtz decomposition for studying atmospheric processes, we compute the contribution of each of the circulation components to heat transport from day- to night-side. Surprisingly, we find that the divergent circulation dominates day-night heat transport in the terrestrial case and accounts for around half of the heat transport for the hot Jupiter. The relative contributions of the rotational and divergent components to day-night heat transport are likely sensitive to multiple planetary parameters and atmospheric processes, and merit further study.

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M. Hammond and N. Lewis
Wed, 24 Feb 21
36/64

Comments: Accepted for publication in Proceedings of the National Academy of Sciences. 11 pages, 10 figures

Oxygen as a control over 2.4 billion years of Earth's atmospheric evolution [EPA]

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http://arxiv.org/abs/2102.11675


Since the formation of the terrestrial planets, atmospheric loss has irreversibly altered their atmospheres, leading to remarkably different surface environments – Earth has remained habitable while Venus and Mars are apparently desolate. The concept of habitability centres around the availability of liquid water which depends greatly on the composition of the atmosphere. While the history of molecular oxygen O$_2$ in Earth’s atmosphere is debated, geological evidence supports at least two major episodes of increasing oxygenation: the Great Oxidation Event and the Neoproterozoic Oxidation Event. Both are thought to have been pivotal for the development and evolution of life. We demonstrate through three-dimensional simulations that atmospheric O$_2$ concentrations on Earth directly control the evolution and distribution of greenhouse gases (such as O$_3$, H$_2$O, CH$_4$ and CO$_2$) and the atmospheric temperature structure. In particular, at $\leq 1$% the present atmospheric level (PAL) of O$_2$, the stratosphere collapses. Our simulations show that a biologically ineffective ozone shield, lower than previously thought, existed during the Proterozoic, with a need for a Phanerozoic ozone shield to allow the emergence of surface life. We find that O$_2$ acts as a valve for the loss rate of atmospheric hydrogen through the exosphere. Estimated levels of hydrogen escape for the Proterozoic eon are all lower than present day, enabling us to establish Earth’s water loss timeline. Furthermore, we demonstrate how O$_2$ on terrestrial exoplanets determines their theoretical transmission spectra, challenging signal-to-nose ratio assumptions contributing to the design of next generation telescopes that will facilitate the characterisation of Earth-like worlds.

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G. Cooke, D. Marsh, C. Walsh, et. al.
Wed, 24 Feb 21
37/64

Comments: 27 pages, 10 figures. Submitted to Nature Geoscience. Figure 5 has been changed from submitted version. Comments are very welcome

Annular Modes of Variability in the Atmospheres of Mars and Titan [EPA]

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http://arxiv.org/abs/2102.10463


Annular modes explain much of the internal variability of Earth’s atmosphere but have never been identified on other planets. Using reanalyses for Mars and a simulation for Titan, we demonstrate that annular modes are prominent in the atmospheres of both worlds, explaining large fractions of their respective variabilities. One mode describes latitudinal shifts of the jet on Mars, as on Earth, and vertical shifts of the jet on Titan. Another describes pulses of midlatitude eddy kinetic energy on all three worlds, albeit with somewhat different characteristics. We further demonstrate that this latter mode has predictive power for regional dust activity on Mars, revealing its usefulness for understanding Martian weather. In addition, our finding of similar annular variability in dynamically diverse worlds indicates its ubiquity across planetary atmospheres, opening a new avenue for comparative planetology as well as an additional consideration for characterization of extrasolar atmospheres.

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J. Battalio and J. Lora
Tue, 23 Feb 21
22/79

Comments: 39 pages, 8 figures

The Physics of Falling Raindrops in Diverse Planetary Atmospheres [EPA]

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http://arxiv.org/abs/2102.09570


The evolution of a single raindrop falling below a cloud is governed by fluid dynamics and thermodynamics fundamentally transferable to planetary atmospheres beyond modern Earth’s. Here, we show how three properties that characterize falling raindrops — raindrop shape, terminal velocity, and evaporation rate — can be calculated as a function of raindrop size in any planetary atmosphere. We demonstrate that these simple, interrelated characteristics tightly bound the possible size range of raindrops in a given atmosphere, independently of poorly understood growth mechanisms. Starting from the equations governing raindrop falling and evaporation, we demonstrate that raindrop ability to vertically transport latent heat and condensible mass can be well captured by a new dimensionless number. Our results have implications for precipitation efficiency, convective storm dynamics, and rainfall rates, which are properties of interest for understanding planetary radiative balance and (in the case of terrestrial planets) rainfall-driven surface erosion.

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K. Loftus and R. Wordsworth
Mon, 22 Feb 21
40/51

Comments: submitted to JGR: Planets; 40 pages, 8 figures, 3 tables, 4 appendices; supporting information with 9 pages, 8 figures, 1 table; associated code at this https URL

Titan: Earth-like on the Outside, Ocean World on the Inside [EPA]

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http://arxiv.org/abs/2102.08472


Thanks to the Cassini-Huygens mission, Titan, the pale orange dot of Pioneer and Voyager encounters has been revealed to be a dynamic, hydrologically-shaped, organic-rich ocean world offering unparalleled opportunities to explore prebiotic chemistry. And while Cassini-Huygens revolutionized our understanding of each of the three layers of Titan–the atmosphere, the surface, and the interior–we are only beginning to hypothesize how these realms interact. In this paper, we summarize the current state of Titan knowledge and discuss how future exploration of Titan would address some of the next decade’s most compelling planetary science questions. We also demonstrate why exploring Titan, both with and beyond the Dragonfly New Frontiers mission, is a necessary and complementary component of an Ocean Worlds Program that seeks to understand whether habitable environments exist elsewhere in our solar system.

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S. MacKenzie, S. Birch, S. Horst, et. al.
Thu, 18 Feb 21
25/66

Comments: Submitted to the PSJ Focus Issue on Ocean World Exploration

Mesospheric nitric oxide model from SCIAMACHY data [CL]

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http://arxiv.org/abs/2102.08455


We present an empirical model for nitric oxide NO in the mesosphere ($\approx$60–90 km) derived from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartoghraphY) limb scan data. This work complements and extends the NOEM (Nitric Oxide Empirical Model; Marsh et al., 2004) and SANOMA (SMR Acquired Nitric Oxide Model Atmosphere; Kiviranta et al., 2018) empirical models in the lower thermosphere. The regression ansatz builds on the heritage of studies by Hendrickx et al. (2017) and the superposed epoch analysis by Sinnhuber et al. (2016) which estimate NO production from particle precipitation.
Our model relates the daily (longitudinally) averaged NO number densities from SCIAMACHY (Bender et al., 2017a, b) as a function of geomagnetic latitude to the solar Lyman-alpha and the geomagnetic AE (auroral electrojet) indices. We use a non-linear regression model, incorporating a finite and seasonally varying lifetime for the geomagnetically induced NO. We estimate the parameters by finding the maximum posterior probability and calculate the parameter uncertainties using Markov chain Monte Carlo sampling. In addition to providing an estimate of the NO content in the mesosphere, the regression coefficients indicate regions where certain processes dominate.

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S. Bender, M. Sinnhuber, P. Espy, et. al.
Thu, 18 Feb 21
42/66

Comments: 13 pages, 6 figures; published in Atmos. Chem. Phys

An improved rovibrational linelist of formaldehyde, \spec{h212c16o} [SSA]

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http://arxiv.org/abs/2102.07423


Published high-resolution rotation-vibration transitions of \spec{h212c16o}, the principal isotopologue of methanal, are analyzed using the MARVEL (Measured Active Rotation-Vibration Energy Levels) procedure. The literature results are augmented by new, high-accuracy measurements of pure rotational transitions within the ground, $\nu_3$, $\nu_4$, and $\nu_6$ vibrational states. Of the \nbNonRedTr\ non-redundant transitions processed, which come from \nbSr\ sources including the present work, \nbValTr\ could be validated, providing \nbEl\ empirical energy levels of \spec{h212c16o}\ with statistically well-defined uncertainties. All the empirical rotational-vibrational energy levels determined are used to improve the accuracy of ExoMol’s AYTY line list for hot formaldehyde. The complete list of collated experimental transitions, the empirical energy levels determined, as well as the extended and improved line list are provided as Supplementary Material.

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A. Al-Derzi, J. Tennyson, S. Yurchenko, et. al.
Tue, 16 Feb 21
43/63

Comments: Accepted for publication on the HITRAN special issue of J. Quant. Spectrosc. Radiat. Transf. (2021)

Fireball characteristics derivable from acoustic data [EPA]

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http://arxiv.org/abs/2102.06574


Near field acoustical signals from fireballs (ranges<200 km), when detected by dense ground networks, may be used to estimate the orientation of the trajectory of a fireball (Pujol et al., 2005) as well as fragmentation locations (Kalenda et al., 2014; Edwards and Hildebrand, 2004). Distinguishing ballistic arrivals (from the cylindrical shock of the fireball)from fragmentation generated signals (quasi-spherical sources) remains a challenge, but are obtainable through analysis of the acoustic path and the timing observed at ground instruments. Here we describe an integrated computer code, termed the Bolide Acoustic Modelling program or BAM, to estimate fireball trajectories and energetics. We develop a new methodology for measuring energy release from bolide fragmentation episodes solely from acoustic measurements and incorporate this into BAM. We also explore the sensitivity of seismo-acoustic fireball solutions and energy estimates to uncertainty in the underlying atmospheric model. Applying BAM to the Stubenberg meteorite producing fireball, we find the total fireball energy from ballistic arrivals to be approximately $5 \times 10^{10}$J which compares favorably to the optical estimate of $4.36 \times 10^{10}$J. The combined fragmentation energy of the Stubenberg event from acoustic data was found to be $1.47^{+0.28}_{-0.12} \times 10^{10}$J, roughly one third of the ballistic or optical total energy. We also show that measuring fireball velocities from acoustic data alone is very challenging but may be possible for slow, deeply penetrating fireballs with shallow entry angles occurring over dense seismic/infrasound networks.

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L. McFadden, P. Brown, D. Vida, et. al.
Mon, 15 Feb 21
46/53

Comments: N/A

Did Mars possess a dense atmosphere during the first ~400 million years? [EPA]

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http://arxiv.org/abs/2102.05976


It is not yet entirely clear whether Mars began as a warm and wet planet that evolved towards the present-day cold and dry body or if it always was cold and dry with just some sporadic episodes of liquid water on its surface. An important clue into this question can be gained by studying the earliest evolution of the Martian atmosphere and whether it was dense and stable to maintain a warm and wet climate or tenuous and susceptible to strong atmospheric escape. We discuss relevant aspects for the evolution and stability of a potential early Martian atmosphere. This contains the solar EUV flux evolution, the formation timescale and volatile inventory of the planet including volcanic degassing, impact delivery and removal, the loss of a catastrophically outgassed steam atmosphere, atmosphere-surface interactions, and thermal and non-thermal escape processes affecting any secondary atmosphere. While early non-thermal escape at Mars before 4 billion years ago (Ga) is poorly understood, particularly in view of its ancient intrinsic magnetic field, research on thermal escape processes indicate that volatile delivery and volcanic degassing cannot counterbalance the strong thermal escape. Therefore, a catastrophically outgassed steam atmosphere of several bars of CO2 and H2O, or CO and H2 for reduced conditions, could have been lost within just a few million years (Myr). Thereafter, Mars likely could not build up a dense secondary atmosphere during its first ~400 Myr but might only have possessed an atmosphere sporadically during events of strong volcanic degassing, potentially also including SO2. This indicates that before ~4.1 Ga Mars indeed might have been cold and dry. A denser CO2- or CO-dominated atmosphere, however, might have built up afterwards but must have been lost later-on due to non-thermal escape processes and sequestration into the ground.

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M. Scherf and H. Lammer
Fri, 12 Feb 21
10/59

Comments: 120 pages, 12 figures. This is a preprint of an article published in Space Science Reviews. The final authenticated version can be found online at this https URL

Global Climate Model Occultation Lightcurves Tested by August 2018 Ground-Based Stellar Occultation [EPA]

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http://arxiv.org/abs/2102.04666


Pluto’s atmospheric profiles (temperature and pressure) have been studied for decades from stellar occultation lightcurves. In this paper, we look at recent Pluto Global Climate Model (GCM) results (3D temperature, pressure, and density fields) from Bertrand et al. (2020) and use the results to generate model observer’s plane intensity fields (OPIF) and lightcurves by using a Fourier optics scheme to model light passing through Pluto’s atmosphere (Young, 2012). This approach can accommodate arbitrary atmospheric structures and 3D distributions of haze. We compared the GCM model lightcurves with the lightcurves observed during the 15-AUG-2018 Pluto stellar occultation. We find that the climate scenario which best reproduces the observed data includes an N2 ice mid-latitude band in the southern hemisphere. We have also studied different haze and P/T ratio profiles: the haze effectively reduces the central flash strength, and a lower P/T ratio both reduces the central flash strength and incurs anomalies in the shoulders of the central flash.

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S. Chen, E. Young, L. Young, et. al.
Wed, 10 Feb 21
16/64

Comments: N/A

Testing a Prototype 1U CubeSat on a Stratospheric Balloon Flight [IMA]

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http://arxiv.org/abs/2102.04847


High-altitude balloon experiments are becoming very popular among universities and research institutes as they can be used for testing instruments eventually intended for space, and for simple astronomical observations of Solar System objects like the Moon, comets, and asteroids, difficult to observe from the ground due to atmosphere. Further, they are one of the best platforms for atmospheric studies. In this experiment, we build a simple 1U CubeSat and, by flying it on a high-altitude balloon to an altitude of about 30 km, where the total payload weighted 4.9 kg and examine how some parameters, such as magnetic field, humidity, temperature or pressure, vary as a function of altitude. We also calibrate the magnetometer to remove the hard iron and soft iron errors. Such experiments and studies through a stratospheric balloon flights can also be used to study the performance of easily available commercial sensors in extreme conditions as well. We present the results of the first flight, which helped us study the functionality of the various sensors and electronics at low temperatures reaching about -40 degrees Celsius. Further the motion of the payload has been tracked throughout this flight. This experiment took place on 8 March 2020 from the CREST campus of the Indian Institute of Astrophysics, Bangalore. Using the results from this flight, we identify and rectify the errors to obtain better results from the subsequent flights.

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A. Srikanth, B. Chandra, B. Nair, et. al.
Wed, 10 Feb 21
59/64

Comments: N/A

Efficient application of the Radiance Enhancement method for detection of the forest fires due to combustion-originated reflectance [CL]

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http://arxiv.org/abs/2102.02136


The existing methods detect the cloud scenes are applied at relatively small spectral range within shortwave upwelling radiative wavelength flux. We have reported a new method for detection of the cloud scenes based on the Radiance Enhancement (RE). This method can be used to cover a significantly wider spectral range from 1100 nm to 1700 nm (Siddiqui et al., 2015) by using datasets from the space-orbiting micro-spectrometer Argus 1000. Due to high sunlight reflection of the smoke originated from the forest or field fires the proposed RE method can also be implemented for detection of combustion aerosols. The approach can be a promising technique for efficient detection and continuous monitor of the seasonal forest and field fires. To the best of our knowledge this is the first report showing how a cloud method can be generalized for efficient detection of the forest fires due to combustion-originated reflectance.

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R. Siddiqui, R. Jagpal, S. Abrarov, et. al.
Thu, 4 Feb 21
38/57

Comments: 20 pages, 12 figures, 1 table

Influence of Biomass Emissions upon Habitability, Biosignatures and Detectability in Earth-like Atmospheres [EPA]

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http://arxiv.org/abs/2102.00220


We investigate atmospheric responses of modeled hypothetical Earth-like planets in the habitable zone of the M-dwarf AD Leonis to reduced oxygen (O2), removed biomass (dead Earth), varying carbon dioxide (CO2) and surface relative humidity (sRH). Results suggest large O2 differences between the reduced O2 and dead scenarios in the lower but not the upper atmosphere. Ozone (O3) and nitrous oxide (N2O) also show this behavior. Methane depends on hydroxyl (OH), its main sink. Abiotic production of N2O occurs in the upper layers. Chloromethane (CH3Cl) decreases everywhere on decreasing biomass. Changing CO2 (from x1 to x100 present atmospheric level (PAL)) and surface relative humidity (sRH) (from 0.1 percent to 100 percent) does not influence CH3Cl as much as lowering biomass. Therefore, CH3Cl can be considered a good biosignature. Changing sRH and CO2 has a greater influence on temperature than O2 and biomass alone. Changing the biomass produces ~6 kilometer (km) in effective height (H) in transmission compared with changing CO2 and sRH ( about 25km). In transmission O2 is discernible at 0.76 microns for greater than 0.1 PAL. The O3 9.6 micron band was weak for the low O2 runs and difficult to discern from dead Earth, however O3 at 0.3 microns could serve as an indicator to distinguish between reduced O2 and dead Earth. Spectral features of N2O and CH3Cl corresponded to some km H. CH4 could be detectable tens of parsecs away with ELT except for the 10-4 and 10-6 PAL O2 scenarios. O2 is barely detectable for the 1 PAL O2 case and unfeasible at lower abundances.

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S. Gebauer, I. Vilović, J. Grenfell, et. al.
Tue, 2 Feb 21
29/86

Comments: N/A

Vertically resolved magma ocean-protoatmosphere evolution: H$_2$, H$_2$O, CO$_2$, CH$_4$, CO, O$_2$, and N$_2$ as primary absorbers [EPA]

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http://arxiv.org/abs/2101.10991


The earliest atmospheres of rocky planets originate from extensive volatile release during magma ocean epochs that occur during assembly of the planet. These establish the initial distribution of the major volatile elements between different chemical reservoirs that subsequently evolve via geological cycles. Current theoretical techniques are limited in exploring the anticipated range of compositional and thermal scenarios of early planetary evolution, even though these are of prime importance to aid astronomical inferences on the environmental context and geological history of extrasolar planets. Here, we present a coupled numerical framework that links an evolutionary, vertically-resolved model of the planetary silicate mantle with a radiative-convective model of the atmosphere. Using this method we investigate the early evolution of idealized Earth-sized rocky planets with end-member, clear-sky atmospheres dominated by either H$_2$, H$_2$O, CO$_2$, CH$_4$, CO, O$_2$, or N$_2$. We find central metrics of early planetary evolution, such as energy gradient, sequence of mantle solidification, surface pressure, or vertical stratification of the atmosphere, to be intimately controlled by the dominant volatile and outgassing history of the planet. Thermal sequences fall into three general classes with increasing cooling timescale: CO, N$_2$, and O$_2$ with minimal effect, H$_2$O, CO$_2$, and CH$_4$ with intermediate influence, and H$_2$ with several orders of magnitude increase in solidification time and atmosphere vertical stratification. Our numerical experiments exemplify the capabilities of the presented modeling framework and link the interior and atmospheric evolution of rocky exoplanets with multi-wavelength astronomical observations.

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T. Lichtenberg, D. Bower, M. Hammond, et. al.
Wed, 27 Jan 21
59/68

Comments: Accepted for publication in JGR Planets; 23 pages, 10 figures; summaries available at this https URL (blog) and this http URL (video)

Jupiter as an Exoplanet: Insights from Cassini Phase Curves [EPA]

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http://arxiv.org/abs/2101.09984


Due to its proximity to Earth, Jupiter of the Solar System serves as a unique case study for gas-giant exoplanets. In the current study, we perform fits of ab initio, reflective, semi-infinite, homogeneous model atmospheres to 61 phase curves from 0.40 to 1.00 $\mu$m, obtained from the Cassini spacecraft, within a Bayesian framework. We reproduce the previous finding that atmospheric models using classic reflection laws (Lambertian, Rayleigh, single Henyey-Greenstein) provide poor fits to the data. Using the double Henyey-Greenstein reflection law, we extract posterior distributions of the single-scattering albedo and scattering asymmetry factors and tabulate their median values and uncertainties. We infer that the aerosols in the Jovian atmosphere are large, irregular, polydisperse particles that produce strong forward scattering together with a narrow backscattering lobe. The near-unity values of the single-scattering albedos imply that multiple scattering of radiation is an important effect. We speculate that the observed narrow backscattering lobe is caused by coherent backscattering of radiation, which is usually associated with Solar System bodies with solid surfaces and regolith. Our findings demonstrate that precise, multi-wavelength phase curves encode valuable information on the fundamental properties of cloud/haze particles. The method described in this Letter enables single-scattering albedos and scattering asymmetry factors to be retrieved from James Webb Space Telescope phase curves of exoplanets.

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K. Heng and L. Li
Tue, 26 Jan 21
38/84

Comments: Submitted to ApJL. 8 pages, 4 figures, 1 table. First referee’s report received. Comments welcome

Dust storm-enhanced gravity wave activity in the Martian thermosphere observed by MAVEN and implication for atmospheric escape [CL]

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http://arxiv.org/abs/2101.07698


Lower atmospheric global dust storms affect the small- and large-scale weather and variability of the whole Martian atmosphere. Analysis of the CO$_2$ density data from the Neutral Gas and Ion Mass Spectrometer instrument (NGIMS) on board NASA’s Mars Atmosphere Volatile EvolutioN (MAVEN) spacecraft show a remarkable increase of GW-induced density fluctuations in the thermosphere during the 2018 major dust storm with distinct latitude and local time variability. The mean thermospheric GW activity increases by a factor of two during the storm event. The magnitude of relative density perturbations is around 20% on average and 40% locally. One and a half months later, the GW activity gradually decreases. Enhanced temperature disturbances in the Martian thermosphere can facilitate atmospheric escape. For the first time, we estimate that, for a 20% and 40% GW-induced disturbances, the net increase of Jeans escape flux of hydrogen is a factor of 1.3 and 2, respectively.

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E. Yiğit, A. Medvedev, M. Benna, et. al.
Wed, 20 Jan 21
41/61

Comments: Accepted for publication in Geophysical Research Letters, 13 pages, 4 figures

A New Method for Aerosol Measurement using Wide-field Photometry [IMA]

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http://arxiv.org/abs/2101.03074


We present a new method to measure the vertical aerosol optical depth (VAOD) during clear nights using a wide-field imager – a CCD camera with a photographic lens on an equatorial mount. A series of 30-second exposures taken at different altitudes above the horizon can be used to measure the VAOD with a precision better than 0.008 optical depths within a few minutes. Such a measurement does not produce any light and is thus suitable for use at sites where other astronomical instruments are located. The precision of the VAOD measurement depends on laboratory calibration of spectral properties of the system and of the response of the camera electronics to varying illumination levels, as well as careful considerations of details of stellar photometry and modelling of the dependence of measured stellar fluxes star color and position within the field of view. The results obtained with robotic setups at the future sites of the Cherenkov Telescope Array show good internal consistency and agreement with the simultaneous measurements from a Sun/Moon Photometer located at the same site.

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J. Ebr, S. Karpov, J. Eliášek, et. al.
Mon, 11 Jan 21
20/65

Comments: Submitted to Astronomical Journal

Telescope Array Bursts, Radio Pulses and Axion Quark Nuggets [CL]

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http://arxiv.org/abs/2101.01722


Telescope Array (TA) experiment has recorded \cite{Abbasi:2017rvx,Okuda_2019} several short time bursts of air shower like events. These bursts are very distinct from conventional single showers, and are found to be strongly correlated with lightnings. In our previous work \cite{Zhitnitsky:2020shd} we proposed that these bursts represent the direct manifestation of the dark matter annihilation events within the so-called axion quark nugget (AQN) model. In the present work we suggest to test this proposal to search for the radio signals in frequency band $\nu\in (0.5-200)$ MHz which must be synchronized with the TA bursts.

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X. Liang and A. Zhitnitsky
Thu, 7 Jan 21
6/58

Comments: 12 pages, 5 figures. arXiv admin note: text overlap with arXiv:2008.04325

Effects of latitude-dependent gravity wave source variations on the middle and upper atmosphere [CL]

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http://arxiv.org/abs/2012.12829


Atmospheric gravity waves (GWs) are generated in the lower atmosphere by various weather phenomena. They propagate upward, carry energy and momentum to higher altitudes, and appreciably influence the general circulation upon depositing them in the middle and upper atmosphere. We use a three-dimensional first-principle general circulation model (GCM) with an implemented nonlinear whole atmosphere GW parameterization to study the global climatology of wave activity and produced effects at altitudes up to the upper thermosphere. The numerical experiments were guided by the GW momentum fluxes and temperature variances as measured in 2010 by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard NASA’s TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite. This includes the latitudinal dependence and magnitude of GW activity in the lower stratosphere for the boreal summer season. The modeling results were compared to the SABER temperature and total absolute momentum flux, and Upper Atmosphere Research Satellite (UARS) data in the mesosphere and lower thermosphere. Simulations suggest that, in order to reproduce the observed circulation and wave activity in the middle atmosphere, smaller than the measured GW fluxes have to be used at the source level in the lower atmosphere. This is because observations contain a broader spectrum of GWs, while parameterizations capture only a portion relevant to the middle and upper atmosphere dynamics. Accounting for the latitudinal variations of the source appreciably improves simulations.

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E. Yiğit, A. Medvedev and M. Ern
Thu, 24 Dec 20
45/73

Comments: Submitted to Frontiers in Astronomy and Space Sciences. Research Topic: “Coupling Processes in Terrestrial and Planetary Atmospheres”

H$_2$O$_2$ Greenhouse Warming on Oxidized Early Mars [EPA]

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http://arxiv.org/abs/2012.10616


The existence of liquid water within an oxidized environment on early Mars has been inferred by the Mn-rich rocks found during recent explorations on Mars. The oxidized atmosphere implied by the Mn-rich rocks would basically be comprised of CO$_2$ and H$_2$O without any reduced greenhouse gases such as H$_2$ and CH$_4$. So far, however, it has been thought that early Mars could not have been warm enough to sustain water in liquid form without the presence of reduced greenhouse gases. Here, we propose that H$_2$O$_2$ could have been the gas responsible for warming the surface of the oxidized early Mars. Our one-dimensional atmospheric model shows that only 1 ppm of H$_2$O$_2$ is enough to warm the planetary surface because of its strong absorption at far-infrared wavelengths, in which the surface temperature could have reached over 273~K for a CO$_2$ atmosphere with a pressure of 3~bar. A wet and oxidized atmosphere is expected to maintain sufficient quantities of H$_2$O$_2$ gas in its upper atmosphere due to its rapid photochemical production in slow condensation conditions. Our results demonstrate that a warm and wet environment could have been maintained on an oxidized early Mars, thereby suggesting that there may be connections between its ancient atmospheric redox state and possible aqueous environment.

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Y. Ito, G. Hashimoto, Y. O, et. al.
Tue, 22 Dec 20
31/89

Comments: 8 pages, 7 figures, published in ApJ

Atomic transitions for adaptive optics [IMA]

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http://arxiv.org/abs/2012.10256


This paper reviews atoms and ions in the upper atmosphere, including the mesospheric metals Na, Fe, Mg$^+$, Si$^+$, Ca$^+$, K and also non-metallic species N, N$^+$, O, H, considering their potential for astronomical adaptive optics. Na and Fe are the best candidates for the creation of polychromatic laser guide stars, with the strongest returns coming from transitions that can be reached by excitation at two wavelengths. Ca$^+$ and Si$^+$ have strong visible-light transitions, but require short wavelengths, beyond the atmospheric cutoff, for excitation from the ground state. Atomic O, N and N$^+$ have strong transitions and high abundances in the mesosphere. The product of column density and cross section for these species can be as high as $10^5$ for O and several hundred for N and N$^+$, making them potential candidates for amplified spontaneous emission. However they require vacuum-ultraviolet wavelengths for excitation.

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R. Yang, J. Hellemeier and P. Hickson
Mon, 21 Dec 20
61/75

Comments: 18 pages, 8 figures

Effects of Spin-Orbit Resonances and Tidal Heating on the Inner Edge of the Habitable Zone [EPA]

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http://arxiv.org/abs/2012.07996


Much attention has been given to the climate dynamics and habitable boundaries of synchronously rotating planets around low mass stars. However, other rotational states are possible, particularly when higher eccentricity orbits can be maintained in a system, including spin-orbit resonant configurations. Additionally, the oscillating strain as a planet moves from periastron to apoastron results in friction and tidal heating, which can be an important energy source. Here, we simulate the climate of ocean-covered planets near the inner edge of the habitable zone around M to solar stars with ROCKE-3D, and leverage the planetary evolution software package, VPLanet, to calculate tidal heating rates for Earth-sized planets orbiting 2600 K and 3000 K stars. This study is the first to use a 3-D General Circulation Model that implements tidal heating to investigate habitability for multiple resonant states. We find that in the absence of tidal heating, the resonant state has little impact on the inner edge, because for a given stellar flux, higher-order states tend to be warmer than synchronous rotators, but for a given temperature, have drier upper atmospheres. However, when strong tidal heating is present, the rotational component implies a strong dependence of habitable conditions on the system evolution and rotational state. Since tidal and stellar heating both decrease with orbital distance, this results in a compact orbital width separating temperate and uninhabitable climates. We summarize these results and also compare ROCKE-3D to previously published simulations of the inner edge that used a modified version of the NCAR CAM4 model.

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C. Colose, J. Haqq-Misra, E. Wolf, et. al.
Wed, 16 Dec 20
73/93

Comments: N/A

Forbidden atomic oxygen emissions in the Martian dayside upper atmosphere [EPA]

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http://arxiv.org/abs/2012.05593


Recently, Nadir and Occultation for Mars Discovery (NOMAD) ultraviolet and visible spectrometer instrument on board the European Space Agency’s ExoMars Trace Gas Orbiter (TGO) simultaneously measured the limb emission intensities for both [OI] 2972 and 5577 {\AA} (green) emissions in the dayside of Martian upper atmosphere. We aim to explore the photochemistry of all these forbidden atomic oxygen emissions ([OI] 2972, 5577, 6300, 6464 {\AA}) in the Martian daylight upper atmosphere and suitable conditions for the simultaneous detection of these emissions lines in the dayside visible spectra. A photochemical model is developed to study the production and loss processes of O(1S) and O(1D) by incorporating various chemical reactions of different O-bearing species in the upper atmosphere of Mars. By reducing Fox (2004) modelled neutral density profiles by a factor of 2, the calculated limb intensity profiles for [OI] 5577 and 2972 {\AA} emissions are found to be consistent with the NOMAD-TGO observations. In this case, at altitudes below 120 km, our modelled limb intensity for [OI] 6300 {\AA} emission is smaller by a factor 2 to 5 compared to that of NOMAD-TGO observation for [OI] 2972 {\AA} emission, and above this distance it is comparable with the upper limit of the observation. We studied various parameters which can influence the limb intensities of these atomic oxygen forbidden emission lines. Our calculated limb intensity for [OI] 6300 {\AA} emission, when the Mars is at near perihelion and for solar maximum condition, suggests that all these forbidden emissions should be observable in the NOMAD-TGO visible spectra taken on the dayside of Martian upper atmosphere. More simultaneous observations of forbidden atomic oxygen emission lines will help to understand the photochemical processes of oxygen-bearing species in the dayside Martian upper atmosphere.

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S. Raghuram, S. Jain and A. Bhardwaj
Fri, 11 Dec 20
5/75

Comments: 12 pages, 5 figures

Chaotic and turbulent temperature fluctuations in atmospheric free convection [CL]

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http://arxiv.org/abs/2002.04562


It is shown, using results of direct numerical simulations, laboratory experiments, measurements in the atmospheric boundary layer, satellite infrared radiances data, the planetary-scale surface-air and tropospheric data, that the temperature fluctuations in atmospheric free convection can be well described by the spatio-temporal distributed chaos approach based on the Bolgiano-Obukhov phenomenology. A possibility of analogous consideration of the atmospheric dynamics on other planets (Mars, Jupiter and Saturn) has been briefly discussed using the data obtained with the Phoenix lander and the infrared observations.

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A. Bershadskii
Wed, 9 Dec 20
18/80

Comments: Extended (new data have been added)

A review of the ocean-atmosphere interactions during tropical cyclones in the north Indian Ocean [CL]

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http://arxiv.org/abs/2012.04384


The north Indian Ocean accounts for 6% of the global tropical cyclones annually. Despite the small fraction of cyclones, some of the most devastating cyclones have formed in this basin, causing extensive damage to the life and property in the north Indian Ocean rim countries. In this review article, we highlight the advancement in research in terms of ocean-atmosphere interaction during cyclones in the north Indian Ocean.

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V. Singh and M. Roxy
Wed, 9 Dec 20
75/80

Comments: N/A

Spectral binning of precomputed correlated-k coefficients [EPA]

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http://arxiv.org/abs/2012.01428


With the major increase in the volume of the spectroscopic line lists needed to perform accurate radiative transfer calculations, disseminating accurate radiative data has become almost as much a challenge as computing it. Considering that many planetary science applications are only looking for heating rates or mid-to-low resolution spectra, any approach enabling such computations in an accurate and flexible way at a fraction of the computing and storage costs is highly valuable. For many of these reasons, the correlated-k approach has become very popular. Its major weakness has been the lack of ways to adapt the spectral grid/resolution of precomputed k-coefficients, making it difficult to distribute a generic database suited for many different applications. Currently, most users still need to have access to a line-by-line transfer code with the relevant line lists or high-resolution cross sections to compute k-coefficient tables at the desired resolution. In this work, we demonstrate that precomputed k-coefficients can be binned to a lower spectral resolution without any additional assumptions, and show how this can be done in practice. We then show that this binning procedure does not introduce any significant loss in accuracy. Along the way, we quantify how such an approach compares very favorably with the sampled cross section approach. This opens up a new avenue to deliver accurate radiative transfer data by providing mid-resolution k-coefficient tables to users who can later tailor those tables to their needs on the fly. To help with this final step, we briefly present Exo_k, an open-access, open-source Python library designed to handle, tailor, and use many different formats of k-coefficient and cross-section tables in an easy and computationally efficient way.

Read this paper on arXiv…

J. Leconte
Fri, 4 Dec 20
5/77

Comments: In press at Astronomy and Astrophysics. The Exo_k library can be found at this http URL along with tutorials, example scripts and notebooks, and an extensive online documentation

Carbonate-Silicate Cycle Predictions of Earth-like Planetary Climates and Testing the Habitable Zone Concept [EPA]

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http://arxiv.org/abs/2012.00819


In the conventional habitable zone (HZ) concept, a CO${2}$-H$_2$O greenhouse maintains surface liquid water. Through the water-mediated carbonate-silicate weathering cycle, atmospheric CO${2}$ partial pressure (pCO${2}$) responds to changes in surface temperature, stabilizing the climate over geologic timescales. We show that this weathering feedback ought to produce a log-linear relationship between pCO${2}$ and incident flux on Earth-like planets in the HZ. However, this trend has scatter because geophysical and physicochemical parameters can vary, such as land area for weathering and CO$_2$ outgassing fluxes. Using a coupled climate and carbonate-silicate weathering model, we quantify the likely scatter in pCO$_2$ with orbital distance throughout the HZ. From this dispersion, we predict a two-dimensional relationship between incident flux and pCO$_2$ in the HZ and show that it could be detected from at least 83 ($2{\sigma}$) Earth-like exoplanet observations. If fewer Earth-like exoplanets are observed, testing the HZ hypothesis from this relationship could be difficult.

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O. Lehmer, D. Catling and J. Krissansen-Totton
Thu, 3 Dec 20
75/81

Comments: Published 12/1/2020 in Nature Communications. The supplemental data and code referenced in this work are available from the Nature Communications website (see DOI below) or by email from the authors

Non-tidal Coupling of the Orbital and Rotational Motions of Extended Bodies [EPA]

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http://arxiv.org/abs/2011.13053


The orbital motions and spin-axis rotations of extended bodies are traditionally considered to be coupled only by tidal mechanisms. The orbit-spin coupling hypothesis supplies an additional mechanism. A reversing torque on rotating extended bodies is identified. The torque effects an exchange of angular momentum between the reservoirs of the orbital and rotational motions. The axis of the torque is constrained to lie within the equatorial plane of the subject body. Hypothesis testing to date has focused on the response to the putative torque of the Martian atmosphere. Atmospheric global circulation model simulations reveal that an episodic strengthening and weakening of meridional overturning circulations should be observable and is diagnostic in connection with the triggering of Martian planet-encircling dust storms. Spacecraft observations obtained during the earliest days of the 2018 Martian global dust storm document a strong intensification of atmospheric meridional motions as predicted under this hypothesis. We review implications for atmospheric physics, for investigations of planetary orbital evolution with rotational energy dissipation, and for theories of gravitation.

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J. Shirley
Mon, 30 Nov 20
19/117

Comments: N/A

Smoke-charged vortices in the stratosphere generated by wildfires and their behaviour in both hemispheres : comparing Australia 2020 to Canada 2017 [CL]

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http://arxiv.org/abs/2011.13239


The two most intense wildfires of the last decade that took place in Canada in 2017 and Australia in 2019-2020 were followed by large injections of smoke in the stratosphere due to pyroconvection. It was discovered by Khaykin et al. (2020, doi:10.1038/s43247-020-00022-5) and Kablick et al. (2020, doi:10.1029/2020GL088101) that, after the Australian event, part of this smoke self-organized as anticyclonic confined vortices that rose in the mid-latitude stratosphere up to 35 km. Based on CALIOP observations and the ERA5 reanalysis, this new study analyzes the Canadian case and find, similarly, that a large plume penetrated the stratosphere by 12 August 2017 and got trapped within a meso-scale anticyclonic structure which travelled across the Atlantic. It then broke into three offsprings that could be followed until mid-October performing three round the world journeys and rising up to 23 km. We analyze the dynamical structure of the vortices produced by these two wildfires and demonstrate how they are maintained by the assimilation of data from instruments measuring the signature of the vortices in the temperature and ozone field. We propose that these vortices can be seen as bubbles of low absolute potential vorticity and smoke carried vertically across the stratification from the troposphere inside the middle stratosphere by their internal heating, against the descending flux of the Brewer-Dobson circulation.

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H. Lestrelin, B. Legras, A. Podglajen, et. al.
Mon, 30 Nov 20
34/117

Comments: Submitted to Atmospheric Chemistry and Physics

Distribution and habitability of (meta)stable brines on present-day Mars [EPA]

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http://arxiv.org/abs/2012.00100


Special Regions on Mars are defined as environments able to host liquid water that meets certain temperature and water activity requirements that allow known terrestrial organisms to replicate, and therefore could be habitable. Such regions would be a concern for planetary protection policies owing to the potential for forward contamination (biological contamination from Earth). Pure liquid water is unstable on the Martian surface, but brines may be present. Experimental work has shown that brines persist beyond their predicted stability region, leading to metastable liquids. Here we show that (meta)stable brines can form and persist from the equator to high latitudes on the surface of Mars for a few percent of the year for up to six consecutive hours, a broader range than previously thought. However, only the lowest eutectic solutions can form, leading to brines with temperatures of less than 225 K. Our results indicate that (meta)stable brines on the Martian surface and shallow subsurface (a few centimeters deep) are not habitable because their water activities and temperatures fall outside the known tolerances for terrestrial life. Furthermore, (meta)stable brines do not meet the Special Regions requirements, reducing the risk for forward contamination and easing threats related to the exploration of the Martian surface.

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E. Rivera-Valentín, V. Chevrier, A. Soto, et. al.
Wed, 2 Dec 20
26/71

Comments: N/A

Phase Shift of Planetary Waves and Wave–Jet Resonance on Tidally Locked Planets [CL]

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http://arxiv.org/abs/2011.14553


Recent studies found that atmospheric superrotation (i.e., west-to-east winds over the equator) on tidally locked planets can modify the phase of planetary waves. But, a clear relationship between the superrotation and the magnitude of the phase shift was not examined. In this study, we re-investigate this problem using a two-dimensional (2D) linear shallow water model with a specified uniform zonal flow. We find that the degree of the phase shift is a monotonic but nonlinear function of the strength of the mean flow, and the phase shift has two limits of -$\pi$ and +$\pi$. The existence of these limits can be explained using the energy balance of the whole system. We further show that a resonance between the Rossby wave and the mean flow occurs when the speed of an eastward jet approaches to the westward phase speed of the Rossby wave, or a resonance between the Kelvin wave and the mean flow happens when the speed of a westward jet approaches to the eastward phase speed of the Kelvin wave. The resonance mechanism is the same as that found in the previous studies on Earth and hot Jupiters. Moreover, in the spin-up period of a 3D global atmospheric general circulation simulation for tidally locked rocky planet, we also find these two phenomena: phase shift and wave–jet resonance. This study improves the understanding of wave–mean flow interactions on tidally locked planets.

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S. Wang and J. Yang
Tue, 1 Dec 20
39/108

Comments: N/A

Aerosols and tides in the martian tropics during southern hemisphere spring equinox from Mars Climate Sounder data [EPA]

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http://arxiv.org/abs/2011.08996


We analyze Mars Climate Sounder temperature and aerosol data in the tropics to study atmospheric tides and their relation to the dust and water ice distributions. Our results from data covering Mars years (MY) 29-35 reveal that MY29 has large amplitude non-migrating thermal tides during southern hemisphere spring equinox that are not observed at the same local time in any other year. It is the nighttime temperatures that are most perturbed compared to other years, with strong temperature inversions at 35-55 km altitude. Analysis of data at different local times reveals that the temperatures and water ice clouds at 03:45 am in MY29 more closely resemble those at 05:00 am in other years, suggesting there was a shift in the phase of the diurnal tide to an earlier local time. This phase shift, and the large amplitude non-migrating thermal tides, appear to be related to early dust activity. Two early dust storms occurred in MY29 around the time there was upwelling over the tropics, associated with the Hadley circulation, enabling the dust to be transported to higher altitudes where it has a larger radiative influence. As well as dust, water ice clouds are also found to influence the tidal structure. Due to the interaction of non-migrating tides, water ice clouds occur in two discrete longitudinal regions at night. The increased radiative cooling results in increased downwelling above the clouds, leading to increased adiabatic warming and a strengthening the temperature inversions.

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L. Steele, A. Kleinboehl, D. Kass, et. al.
Thu, 19 Nov 20
77/83

Comments: 27 pages, 11 Figures

Deep convection-driven vortex formation on Jupiter and Saturn [EPA]

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http://arxiv.org/abs/2011.07263


The surface of both Jupiter and Saturn has magnificent vortical storms which help shape the dynamic nature of their atmospheres. Land- and space-based observational campaigns over time have established several properties of these vortices, with some being similar between the two planets, while others are different. Shallow-water hydrodynamics, where the vortices are treated as shallow weather-layer phenomenon, is commonly evoked for explaining their formation and properties. Here we report novel formation mechanisms for vortices where the primary driving mechanism is the deep planetary convection occurring in these planets. Using three dimensional simulations of turbulent convection in rotating spherical shells, we propose two ideas: (1) rotating turbulent convection generates deep axially-aligned cyclones and anticyclones; (2) a deep planetary dynamo acts to promote additional anticyclones, some as large as Jupiter’s Great Red Spot, in an overlying atmospheric layer. We use these ideas to interpret several observational properties of vortices on Jupiter and Saturn.

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R. Yadav, M. Heimpel and J. Bloxham
Tue, 17 Nov 20
48/83

Comments: 16 Pages, 3 main and 7 supplementary figures, 2 animations on youtube

A Recharge Oscillator Model for Interannual Variability in Venus' Clouds [EPA]

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http://arxiv.org/abs/2010.16122


Sulfur dioxide is a radiatively and chemically important trace gas in the atmosphere of Venus and its abundance at the cloud-tops has been observed to vary on interannual to decadal timescales. This variability is thought to come from changes in the strength of convection which transports sulfur dioxide to the cloud-tops, {although} the dynamics behind such convective variability are unknown. Here we propose a new conceptual model for convective variability that links the radiative effects of water abundance at the cloud-base to convective strength within the clouds, which in turn affects water transport within the cloud. The model consists of two coupled equations which are identified as a recharge-discharge oscillator. The solutions of the coupled equations are finite amplitude sustained oscillations in convective strength and cloud-base water abundance on 3-9 year timescales. The characteristic oscillation timescale is given by the geometric mean of the radiative cooling time and the eddy mixing time near the base of the convective clouds.

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P. Kopparla, A. Seshadri, T. Imamura, et. al.
Mon, 2 Nov 20
22/56

Comments: 19 pages, 6 figures, accepted in JGR Planets

Bolometric Night Sky Temperature and Subcooling of Telescope Structures [IMA]

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http://arxiv.org/abs/2010.01978


Context. The term sky temperature is used in the literature in different contexts which often leads to confusion. In this work, we study $T_\text{sky}$, the effective bolometric sky temperature at which a hemispherical black body would radiate the same power onto a flat horizontal structure on the ground as the night sky, integrated over the entire thermal wavelength range of $1-100\,\mu$m. We then analyze the thermal physics of radiative cooling with special focus on telescopes and discuss mitigation strategies.
Aims. The quantity $T_\text{sky}$ is useful to quantify the subcooling in telescopes which can deteriorate the image quality by introducing an Optical Path Difference (OPD) and induce thermal stress and mechanical deflections on structures.
Methods. We employ the Cerro Paranal Sky Model of the European Southern Observatory to derive a simple formula of $T_\text{sky}$ as a function of atmospheric parameters. The structural subcooling and the induced OPD are then expressed as a function of surface emissivity, sky view factor, local air speed and structure dimensions.
Results. At Cerro Paranal (2600 m) and Cerro Armazones (3060 m) in the Atacama desert, $T_\text{sky}$ towards the zenith mostly lies $20-50$ Kelvin below the ambient temperature near the ground, depending strongly on the precipitable water vapor (PWV) column in the atmosphere. The temperature difference can decrease by several Kelvin for higher zenith distances. The subcooling OPD scales linearly to quadratically with the telescope diameter and is inversely proportional to the local air speed near the telescope structure.

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R. Holzlöhner, S. Kimeswenger, W. Kausch, et. al.
Tue, 6 Oct 2020
38/85

Comments: 14 pages, 16 figures

Effect of the surface shape of a large space body on its fragmentation in a planetary atmosphere [EPA]

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http://arxiv.org/abs/2010.01095


Employing the finite element and computational fluid dynamics methods, we have determined the conditions for the fragmentation of space bodies or preservation of their integrity when they penetrate into the Earth’s atmosphere. The origin of forces contributing to the fragmentation of space iron bodies during the passage through the dense layers of the planetary atmosphere has been studied. It was shown that the irregular shape of the surface can produce transverse aerodynamic forces capable of causing deformation stress in the body exceeding the tensile strength threshold of iron.

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D. Khrennikov, A. Titov, A. Ershov, et. al.
Mon, 5 Oct 20
25/61

Comments: 9 pages, 14 figures

CRAHCN-O: A Consistent Reduced Atmospheric Hybrid Chemical Network Oxygen Extension for Hydrogen Cyanide and Formaldehyde Chemistry in CO2-, N2-, H2O-, CH4-, and H2-Dominated Atmospheres [CL]

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http://arxiv.org/abs/2009.12375


Hydrogen cyanide (HCN) and formaldehyde (H2CO) are key precursors to biomolecules such as nucleobases and amino acids in planetary atmospheres; However, many reactions which produce and destroy these species in atmospheres containing CO2 and H2O are still missing from the literature. We use a quantum chemistry approach to find these missing reactions and calculate their rate coefficients using canonical variational transition state theory and Rice-Ramsperger-Kassel-Marcus/master equation theory at the BHandHLYP/aug-cc-pVDZ level of theory. We calculate the rate coefficients for 126 total reactions, and validate our calculations by comparing with experimental data in the 39% of available cases. Our calculated rate coefficients are most frequently within an factor of 2 of experimental values, and generally always within an order of magnitude of these values. We discover 45 previously unknown reactions, and identify 6 from this list that are most likely to dominate H2CO and HCN production and destruction in planetary atmospheres. We highlight $^1$O + CH3 $\rightarrow$ H2CO + H as a new key source, and H2CO + $^1$O $\rightarrow$ HCO + OH as a new key sink, for H2CO in upper planetary atmospheres. In this effort, we develop an oxygen extension to our consistent reduced atmospheric hybrid chemical network (CRAHCN-O), building off our previously developed network for HCN production in N2-, CH4-, and H2-dominated atmospheres (CRAHCN). This extension can be used to simulate both HCN and H2CO production in atmospheres dominated by any of CO2, N2, H2O, CH4, and H2.

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B. Pearce, P. Ayers and R. Pudritz
Wed, 30 Sep 2020
18/86

Comments: Accepted for publication in J Phys Chem A, 21 pages, 4 tables, 35 supplementary pages

Gamma Ray Bursts: Not so Much Deadlier than We Thought [EPA]

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http://arxiv.org/abs/2009.14078


We analyze the additional effect on planetary atmospheres of recently detected gamma-ray burst afterglow photons in the range up to 1 TeV. For an Earth-like atmosphere we find that there is a small additional depletion in ozone versus that modeled for only prompt emission. We also find a small enhancement of muon flux at the planet surface. Overall, we conclude that the additional afterglow emission, even with TeV photons, does not result in a significantly larger impact over that found in past studies.

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B. Thomas, D. Atri and A. Melott
Wed, 30 Sep 2020
50/86

Comments: Submitted to MNRAS

The Phase-curve Signature of Condensible Water-rich Atmospheres on Slowly Rotating Tidally Locked Exoplanets [EPA]

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http://arxiv.org/abs/2009.13638


We use an idealized three-dimensional general circulation model to study condensible-rich atmospheres with an ineffective cold trap on slowly rotating tidally locked terrestrial planets. In particular, we show the climate dynamics in a thin and temperate atmosphere with condensible water vapor. The similarities between our thin and temperate atmosphere and the warm and thick atmosphere approaching the water vapor runaway greenhouse in previous works are discussed, including the reversal of the thermal emission between the day and night hemispheres. Different from the transit spectroscopy of water vapor that depends on the absolute amount of atmospheric water vapor, the contrast between the dayside and nightside thermal emission provides information regarding the relative ratio of water vapor to the background atmosphere as well as the atmospheric pressure near the substellar tropopause and the emission level on the nightside on potentially habitable worlds.

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F. Ding and R. Pierrehumbert
Wed, 30 Sep 2020
61/86

Comments: 15 pages, 4 figures

The impact of climate change on astronomical observations [IMA]

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http://arxiv.org/abs/2009.11779


Climate change is affecting and will increasingly affect astronomical observations. In this paper, we investigated the role some key weather parameters play in the quality of astronomical observations, and analysed their long-term trends (longer than 30 years) in order to grasp the impact of climate change on current and future observations. In this preliminary study, we specifically analysed four parameters, the temperature, the surface layer turbulence, the wind speed at the jetstream layer and the humidity. The analyses is conducted with data from the Very Large Telescope (VLT), operated by the European Southern Observatory (ESO), located at Cerro Paranal in the Atacama desert, Chile, which is one of the driest places on Earth. To complete the data from the various sensors installed at Paranal, we used the fifth generation and 20th century European Centre Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis of the global climate, ERA5 (from 1980 to now) and ERA20C (from 1900 to 2010), which we interpolated at the Paranal observatory location. In addition, we also explored climate projections in this region, using the Coupled Model Intercomparison Project Phase 6 (CMIP6) multi-model ensemble, under the worst-case climate change Shared Socio-Economic Pathways (SSP5-8.5) scenario. Further investigation is needed to better understand the underlying mechanisms of change, as well as to assess the severity of the impact.

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F. Cantalloube, J. Milli, C. Böhm, et. al.
Fri, 25 Sep 20
-1815/62

Comments: Originated at EAS 2020 conference, sustainability session by this https URL – published in Nature Astronomy, September 2020. Free access this https URL (courtesy of Nature Astronomy)

The Equatorial Jet Speed on Tidally Locked Planets: I — Terrestrial Planets [EPA]

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http://arxiv.org/abs/2009.00358


The atmospheric circulation of tidally locked planets is dominated by a superrotating eastward equatorial jet. We develop a predictive theory for the formation of this jet, proposing a mechanism in which the three-dimensional stationary waves induced by the day-night forcing gradient produce an equatorial acceleration. This is balanced in equilibrium by an interaction between the resulting jet and the vertical motion of the atmosphere. The three-dimensional structure of the zonal acceleration is vital to this mechanism.
We demonstrate this mechanism in a hierarchy of models. We calculate the three-dimensional stationary waves induced by the forcing on these planets, and show the vertical structure of the zonal acceleration produced by these waves, which we use to suggest a mechanism for how the jet forms. GCM simulations are used to confirm the equilibrium state predicted by this mechanism, where the acceleration from these waves is balanced by an interaction between the zonal-mean vertical velocity and the jet. We derive a simple model of this using the “Weak Temperature Gradient” approximation, which gives an estimate of the jet speed on a terrestrial tidally locked planet.
We conclude that the proposed mechanism is a good description of the formation of an equatorial jet on a terrestrial tidally locked planet, and should be useful for interpreting observations and simulations of these planets. The mechanism requires assumptions such as a large equatorial Rossby radius and weak acceleration due to transient waves, and a different mechanism may produce the equatorial jets on gaseous tidally locked planets.

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M. Hammond, S. Tsai and R. Pierrehumbert
Wed, 2 Sep 20
-1355/65

Comments: Accepted by ApJ

Annual cycle and longitudinal structure of tropical eddy and mean momentum fluxes [CL]

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http://arxiv.org/abs/2008.07768


The longitudinal structure and annual cycle of mean meridional and eddy momentum fluxes in the tropical upper troposphere are studied. In zonal mean, these two terms oppose each other and peak during the Indian summer monsoon. This zonal mean character arises from a rich longitudinal structure that is revealed by splitting the globe into three zones, namely, the Asia-West Pacific (AWP), central Pacific-West Atlantic (CP-WA) and African sectors. The mean convergence term is cohesive across all three regions, has a single peak in the boreal summer and always acts to decelerate the zonal flow. A Helmholtz decomposition shows that the advection of absolute vorticity by the divergent meridional wind in localized cross-equatorial cells is responsible for the coherent nature of the mean convergence across all sectors.
On the other hand, the eddy convergence goes from being small and seasonally invariant in the African region to one with large seasonal maxima (minima) in AWP (CP-WA) sector that accelerate (decelerate) the zonal mean flow. The disparate nature the eddy flux in the AWP and CP-WA regions is in the winter season and is due to the tropical and extratropical origin of waves, respectively. In summer, the AWP region accounts for almost all of the eddy flux convergence. In fact, the leading role of the rotational zonal – divergent meridional component in the zonal mean eddy flux does not hold in individual sectors. Finally, through the year, the CP-WA region is where the local overturning cell is strongly influenced by eddy activity.

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A. Thakur and J. Sukhatme
Wed, 19 Aug 20
-1044/52

Comments: N/A

The Mysterious Bursts observed by Telescope Array and Axion Quark Nuggets [CL]

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http://arxiv.org/abs/2008.04325


Telescope Array (TA) experiment has recorded \cite{Abbasi:2017rvx,Okuda_2019} several short time bursts of air shower like events. These bursts are very distinct from conventional single showers, and are found to be strongly correlated with lightnings. We propose that these bursts represent the direct manifestation of the dark matter annihilation events within the so-called axion quark nugget (AQN) model, which was originally invented for completely different purpose to explain the observed similarity between the dark and the visible components in the Universe, i.e. $\Omega_{\rm DM}\sim \Omega_{\rm visible}$ without any fitting parameters. We support this proposal by demonstrating that the observations \cite{Abbasi:2017rvx,Okuda_2019}, including the frequency of appearance, temporal and spatial distributions, intensity, and other related observables are nicely match the emission features of the AQNs propagating in the atmosphere under thunderstorm. We propose to test these ideas by reanalyzing the existing data by increasing the cutoff time scale $\Delta t=1$ ms for the bursts. We also suggest to test this proposal by analyzing the correlations with proper infrasound and seismic instruments.

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A. Zhitnitsky
Wed, 12 Aug 20
-861/63

Comments: 13 pages

HCN production in Titan's Atmosphere: Coupling quantum chemistry and disequilibrium atmospheric modeling [EPA]

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http://arxiv.org/abs/2008.04312


Hydrogen cyanide (HCN) is a critical reactive source of nitrogen for building key biomolecules relevant for the origin of life. Still, many HCN reactions remain uncharacterized by experiments and theory, and the complete picture of HCN production in planetary atmospheres is not fully understood. To improve this situation, we develop a novel technique making use of computational quantum chemistry, experimental data, and atmospheric numerical simulations. First, we use quantum chemistry simulations to explore the entire field of possible reactions for a list of primary species in N2-, CH4-, and H2-dominated atmospheres. In this process, we discover 33 new reactions with no previously known rate coefficients. From here, we develop a consistent reduced atmospheric hybrid chemical network (CRAHCN) containing experimental values when available, and our calculated rate coefficients otherwise. Next, we couple CRAHCN to a 1D chemical kinetic model (ChemKM) to compute the HCN abundance as a function of atmospheric depth on Titan. Our simulated atmospheric HCN profile agrees very well with the Cassini observations. CRAHCN contains 104 reactions however nearly all of the simulated atmospheric HCN profile can be obtained using a scaled down network of only 19 dominant reactions. From here, we form a complete picture of HCN chemistry in Titan’s atmosphere, from the dissociation of the main atmospheric species, down to the direct production of HCN along 4 major channels. One of these channels was first discovered and characterized in Pearce et al. (2019) and this work.

Read this paper on arXiv…

B. Pearce, K. Molaverdikhani, R. Pudritz, et. al.
Wed, 12 Aug 20
-854/63

Comments: 23 pages (+41 supplementary pages), 5 figures, 5 tables (+11 supplementary tables), Accepted for publication in ApJ

Thirteen years of Weather Statistics at San Pedro Martir Observatory [IMA]

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http://arxiv.org/abs/2008.02402


We present weather statistics for thirteen years of data gathered with the meteorological stations at Observatorio Astron\’omico Nacional in the Sierra San Pedro M\’artir (OAN-SPM) over the period 2007-2019. These weather stations include sensors that measure temperature, atmospheric pressure, relative humidity, precipitation and wind conditions, among other climatological variables. The median values of the air temperature are $10.3^{\circ}$ C and $7.0^{\circ}$ C for daytime and nighttime, respectively. The relative humidity follows a seasonal variation with April-June being the driest months while July-September being the most humid. The median values for the sustained wind speed are 11 and 14 km hr$^{-1}$ for daytime and nighttime data, respectively. Preferred wind directions are SSW and North. Sustained winds are stronger at night and during December, January and February. Our data indicate an annual mean rain precipitation of 313 mm, most of which occurs during the summer season as afternoon thunderstorms.

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I. Plauchu-Frayn, E. Colorado, M. Richer, et. al.
Fri, 7 Aug 20
-754/46

Comments: 43 pages and 24 figures. Accepted for publication in RMxAA

Oceanic and atmospheric methane cycling in the cGENIE Earth system model [CL]

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http://arxiv.org/abs/2007.15053


The methane cycle is a key component of the Earth system that links planetary climate, biological metabolism, and the global biogeochemical cycles of carbon, oxygen, sulfur, and hydrogen. However, currently lacking is a numerical model capable of simulating a diversity of environments in the ocean where methane can be produced and destroyed, and with the flexibility to be able to explore not only relatively recent perturbations to Earth’s methane cycle but also to probe methane cycling and associated climate impacts under the reducing conditions characteristic of most of Earth history and likely widespread on other Earth-like planets. Here, we present an expansion of the ocean-atmosphere methane cycle in the intermediate-complexity Earth system model cGENIE, including parameterized atmospheric photochemistry and schemes for microbial methanogenesis, aerobic methanotrophy, and anaerobic oxidation of methane. We describe the model framework, compare model parameterizations against modern observations, and illustrate the flexibility of the model through a series of example simulations. Though we make no attempt to rigorously tune default model parameters, we find that simulated atmospheric methane levels and marine dissolved methane distributions are generally in good agreement with empirical constraints for the modern and recent Earth. Finally, we illustrate the model’s utility in understanding the time-dependent behavior of the methane cycle resulting from transient carbon injection into the atmosphere, and present model ensembles that examine the effects of oceanic chemistry and the thermodynamics of microbial metabolism on steady-state atmospheric methane abundance.

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C. Reinhard, S. Olson, S. Turner, et. al.
Fri, 31 Jul 20
-633/69

Comments: Manuscript in review at Geoscientific Model Development

Detection of polarization neutral points in observations of the combined corona and sky during the 21 August 2017 total solar eclipse [SSA]

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http://arxiv.org/abs/2007.12482


We report the results of polarimetric observations of the total solar eclipse of 21 August 2017 from Rexburg, Idaho (USA). We use three synchronized DSLR cameras with polarization filters oriented at 0{\deg}, 60{\deg}, and 120{\deg} to provide high-dynamic-range RGB polarization images of the corona and surrounding sky. We measure tangential coronal polarization and vertical sky polarization, both as expected. These observations provide detailed detections of polarization neutral points above and below the eclipsed Sun where the coronal polarization is canceled by the sky polarization. We name these special polarization neutral points after Minnaert and Van de Hulst.

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F. Snik, S. Bos, S. Brackenhoff, et. al.
Mon, 27 Jul 20
-575/60

Comments: Part of the Applied Optics special feature issue on Light and Color in Nature

The initial stage of cloud lightning imaged in high-resolution [CL]

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http://arxiv.org/abs/2007.03934


With LOFAR we have been able to image the development of lightning flashes with meter-scale accuracy and unprecedented detail. We discuss the primary steps behind our most recent lightning mapping method. To demonstrate the capabilities of our technique we show and interpret images of the first few milliseconds of two intra-cloud flashes. In all our flashes the negative leaders propagate in the charge layer below the main negative charge. Among several interesting features we show that in about 2~ms after initiation the Primary Initial Leader triggers the formation of a multitude (more than ten) negative leaders in a rather confined area of the atmosphere. From these only one or two continue to propagate after about 30~ms to extend over kilometers horizontally while another may propagate back to the initiation point. We also show that normal negative leaders can transition into an initial-leader like state, potentially in the presence of strong electric fields. In addition, we show some initial breakdown pulses that occurred during the primary initial leader, and even during two “secondary” initial leaders that developed out of stepped leaders.

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O. Scholten, B. Hare, J. Dwyer, et. al.
Thu, 9 Jul 20
4/70

Comments: Submitted to Journal of geophysics research: Atmospheres

Radio emission from negative lightning leader steps reveals inner meter-scale structure [CL]

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http://arxiv.org/abs/2007.03231


We use the Low Frequency ARray (LOFAR) to probe the dynamics of the stepping process of negatively-charged plasma channels (negative leaders) in a lightning discharge. We observe that at each step of a leader, multiple pulses of VHF (30~–~80 MHz) radiation are emitted in short-duration bursts ($<10\ \mu$s). This is evidence for streamer formation during corona flashes that occur with each leader step, which has not been observed before in natural lightning and it could help explain X-ray emission from lightning leaders, as X-rays from laboratory leaders tend to be associated with corona flashes. Surprisingly we find that the stepping length is very similar to what was observed near the ground, however with a stepping time that is considerably larger, which as yet is not understood. These results will help to improve lightning propagation models, and eventually lightning protection models.

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B. Hare, O. Scholten, J. Dwyer, et. al.
Wed, 8 Jul 20
65/77

Comments: 5 pages

Hurricane genesis is favorable on terrestrial exoplanets orbiting late-type M dwarf stars [EPA]

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http://arxiv.org/abs/2006.15120


Hurricanes are one of the most extreme storm systems that occur on Earth, characterized by strong rainfall and fast winds. The terrestrial exoplanets that will be characterized with future infrared space telescopes orbit M dwarf stars. As a result, the best observable terrestrial exoplanets have vastly different climates than Earth, with a large dayside-to-nightside irradiation contrast and relatively slow rotation. Hurricanes may affect future observations of terrestrial exoplanets because they enhance the vertical transport of water vapor and could influence ocean heat transport. In this work, we explore how the environment of terrestrial exoplanets orbiting M dwarf stars affects the favorability of hurricane genesis (formation). To do so, we apply metrics developed to understand hurricane genesis on Earth to three-dimensional climate models of ocean-covered exoplanets orbiting M dwarf stars. We find that hurricane genesis is most favorable on intermediate-rotating tidally locked terrestrial exoplanets with rotation periods of $\sim 8-10~\mathrm{days}$. As a result, hurricane genesis is most favorable for terrestrial exoplanets in the habitable zones of late-type M dwarf stars. The peak in the favorability of hurricane genesis at intermediate rotation occurs because sufficient spin is required for hurricane genesis, but the vertical wind shear on fast-rotating terrestrial exoplanets disrupts hurricane genesis. We find that hurricane genesis is less favorable on slowly rotating terrestrial exoplanets, which agrees with previous work. Future work using simulations that resolve hurricane genesis and evolution can test our expectations for how the environment affects the favorability of hurricane genesis on tidally locked terrestrial exoplanets.

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T. Komacek, D. Chavas and D. Abbot
Mon, 29 Jun 20
79/79

Comments: Accepted at ApJ, 13 pages, 5 figures, 2 tables

A universal smartphone add-on for portable spectroscopy and polarimetry: iSPEX 2 [CL]

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http://arxiv.org/abs/2006.01519


Spectropolarimetry is a powerful technique for remote sensing of the environment. It enables the retrieval of particle shape and size distributions in air and water to an extent that traditional spectroscopy cannot. SPEX is an instrument concept for spectropolarimetry through spectral modulation, providing snapshot, and hence accurate, hyperspectral intensity and degree and angle of linear polarization. Successful SPEX instruments have included groundSPEX and SPEX airborne, which both measure aerosol optical thickness with high precision, and soon SPEXone, which will fly on PACE. Here, we present a low-cost variant for consumer cameras, iSPEX 2, with universal smartphone support. Smartphones enable citizen science measurements which are significantly more scaleable, in space and time, than professional instruments. Universal smartphone support is achieved through a modular hardware design and SPECTACLE data processing. iSPEX 2 will be manufactured through injection molding and 3D printing. A smartphone app for data acquisition and processing is in active development. Production, calibration, and validation will commence in the summer of 2020. Scientific applications will include citizen science measurements of aerosol optical thickness and surface water reflectance, as well as low-cost laboratory and portable spectroscopy.

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O. Burggraaff, A. Perduijn, R. Hek, et. al.
Wed, 3 Jun 20
24/83

Comments: 16 pages, 11 figures, SPIE Defense + Commercial Sensing 2020

Dynamics of spherical space debris of different sizes falling to Earth [EPA]

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http://arxiv.org/abs/2006.00853


Space debris larger than 1 cm can damage space instruments and impact Earth. The low-Earth orbits (at heights smaller than 2000 km) and orbits near the geostationary- Earth orbit (at 35786 km height) are especially endangered, because most satellites orbit at these latitudes. With current technology space debris smaller than 10 cm cannot be tracked. Smaller space debris burn up and evaporate in the atmosphere, but larger ones fall to the Earth’s surface. For practical reasons it would be important to know the mass, composition, shape, velocity, direction of motion and impact time of space debris re-entering the atmosphere and falling to Earth. Since it is very difficult to measure these physical parameters, almost nothing is known about them. To partly fill this gap, we performed computer modelling with which we studied the celestial mechanics of spherical re-entry particles falling to Earth due to air drag.We determined the time, velocity and angle of impact as functions of the launch height, direction, speed and size of spherical re-entry particles. Our results can also be used for semi-spherical meteoroid particles of the interplanetary dust entering the Earth’s atmosphere.

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J. Slíz-Balogh, D. Horváth, R. Szabó, et. al.
Tue, 2 Jun 20
18/90

Comments: 16 pages, 8 figures

A Long-lived Sharp Disruption on the Lower Clouds of Venus [EPA]

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http://arxiv.org/abs/2005.13540


Planetary-scale waves are thought to play a role in powering the yet-unexplained atmospheric superrotation of Venus. Puzzlingly, while Kelvin, Rossby and stationary waves manifest at the upper clouds (65–70 km), no planetary-scale waves or stationary patterns have been reported in the intervening level of the lower clouds (48–55 km), although the latter are probably Lee waves. Using observations by the Akatsuki orbiter and ground-based telescopes, we show that the lower clouds follow a regular cycle punctuated between 30$^{\circ}$N–40$^{\circ}$S by a sharp discontinuity or disruption with potential implications to Venus’s general circulation and thermal structure. This disruption exhibits a westward rotation period of $\sim$4.9 days faster than winds at this level ($\sim$6-day period), alters clouds’ properties and aerosols, and remains coherent during weeks. Past observations reveal its recurrent nature since at least 1983, and numerical simulations show that a nonlinear Kelvin wave reproduces many of its properties.

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J. Peralta, T. Navarro, C. Vun, et. al.
Fri, 29 May 20
26/75

Comments: 21 pages, 10 figures, 2 animated figures and 2 tables

The STONE curve: A ROC-derived model performance assessment tool [CL]

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http://arxiv.org/abs/2005.03542


A new model validation and performance assessment tool is introduced, the sliding threshold of observation for numeric evaluation (STONE) curve. It is based on the relative operating characteristic (ROC) curve technique, but instead of sorting all observations in a categorical classification, the STONE tool uses the continuous nature of the observations. Rather than defining events in the observations and then sliding the threshold only in the classifier (model) data set, the threshold is changed simultaneously for both the observational and model values, with the same threshold value for both data and model. This is only possible if the observations are continuous and the model output is in the same units and scale as the observations, that is, the model is trying to exactly reproduce the data. The STONE curve has several similarities with the ROC curve, plotting probability of detection against probability of false detection, ranging from the (1,1) corner for low thresholds to the (0,0) corner for high thresholds, and values above the zero-intercept unity-slope line indicating better than random predictive ability. The main difference is that the STONE curve can be nonmonotonic, doubling back in both the x and y directions. These ripples reveal asymmetries in the data-model value pairs. This new technique is applied to modeling output of a common geomagnetic activity index as well as energetic electron fluxes in the Earth’s inner magnetosphere. It is not limited to space physics applications but can be used for any scientific or engineering field where numerical models are used to reproduce observations.

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M. Liemohn, A. Azari, N. Ganushkina, et. al.
Fri, 8 May 20
64/72

Comments: 19 pages, including 4 figures. Currently in second-round review with “Earth and Space Science”: this https URL

Glaciological window into the pace of the organic carbon cycle [CL]

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http://arxiv.org/abs/2005.02806


The glaciological record of atmospheric composition suggests O2 has declined over the last 800000 years at an average rate of 0.3 x 1012 mol (Tmol) O2 yr-1. Because the geological carbon cycle regulates long term atmospheric oxygen concentrations, fluctuations in atmospheric O2 are typically attributed to an imbalance between the weathering of organic carbon (OC) and reduced sulfur on land, a sink of atmospheric O2, and the burial of OC and reduced sulfur in marine sediments, a source of O2. Here we compile and confront a database of C, Fe, S and H exchanges between the fluid Earth (atmosphere, ocean, biosphere) and lithosphere (crust and upper mantle) with the record of deoxygenation to quantify organic carbon sources and sinks in the Cenozoic. We show that the subduction of oxidized oceanic lithosphere and degassing of reduced gas from the Earth’s interior is a sink of oxygen, and that this sink significantly exceeds the rate of atmospheric deoxygenation in the Pleistocene. A relative constancy of atmospheric O2 in the Cenozoic requires that the organic carbon cycle was a net source of O2 and sink of CO2, photosynthesis outpaced respiration by an average of ca 40 MtC yr-1 over the last 50 million years. The cost for the relatively invariant atmospheric oxygen concentration is the coexistence of two photosynthetically-driven imbalances in the cycles of iron and carbon that offset each other to near perfection. The weak escape of OC from continents and oceans to the lithosphere is more intriguing. It demonstrates that the organic carbon cycle remains under surprisingly strong kinetic control, despite evolution/optimization of respiratory metabolisms and rising atmospheric O2 for more than 2.4 billion years.

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G. Emmanuel
Thu, 7 May 20
7/62

Comments: N/A

A study of daytime convective vortices and turbulence in the martian Planetary Boundary Layer based on half-a-year of InSight atmospheric measurements and Large-Eddy Simulations [EPA]

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http://arxiv.org/abs/2005.01134


Studying the atmospheric Planetary Boundary Layer (PBL) is crucial to understand the climate of a planet. The meteorological measurements by the instruments onboard InSight make a uniquely rich dataset to study the active turbulent dynamics of the daytime PBL on Mars. Here we use the high-sensitivity continuous pressure, wind, temperature measurements in the first 400 sols of InSight operations to analyze convective gusts, cells, and vortices in Mars’ daytime PBL. We compare the InSight measurements to turbulence-resolving Large-Eddy Simulations (LES). The daytime PBL turbulence at the InSight landing site is found to be very active, with clearly identified signatures of convective cells and a vast population of almost 10,000 recorded vortex encounters, adequately represented by a power-law with a 3.5 exponent in agreement with LES results. While the daily variability of vortex encounters at the InSight landing site can be explained by the statistical nature of turbulence, the seasonal variability is strongly correlated with ambient wind speed, which is supported by LES. However, wind gustiness is more correlated to surface temperature than ambient wind speed, confirming the radiative control of the daytime martian PBL; and fewer convective vortices are forming in LES when the background wind is doubled. Thus, the long-term seasonal variability of vortex encounters at the InSight landing site is mainly controlled by the advection of convective vortices by the ambient wind speed. Typical tracks followed by vortices forming in the LES show a similar distribution in direction and length as orbital imagery of the InSight region.

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A. Spiga, N. Murdoch, R. Lorenz, et. al.
Tue, 5 May 20
56/75

Comments: 39 pages, 16 figures, manuscript not yet peer-reviewed and submitted to Journal of Geophysical Research Planets (InSight special issue)

Anelastic equatorial waves with the complete Coriolis terms [CL]

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http://arxiv.org/abs/2004.15017


This study derives a complete set of equatorially confined wave solutions from an anelastic equation set with the complete Coriolis terms, which include both the vertical and meridional planetary vorticity. The propagation mechanism can change with the effective static stability. When the effective static stability reduces to neutral, buoyancy ceases, but the role of buoyancy as an eastward-propagation mechanism is replaced by the compressional beta-effect, i.e., vertical density-weighted advection of the meridional planetary vorticity. For example, the Kelvin mode becomes a compressional Rossby mode. Compressional Rossby waves are meridional vorticity disturbances that propagate eastward owing to the compressional beta-effect. The compressional Rossby wave solutions can serve as a benchmark to validate the implementation of the nontraditional Coriolis terms (NCTs); with an effectively neutral condition and initial large-scale disturbances given a half vertical wavelength spanning the troposphere on Earth, compressional Rossby waves are expected to propagate eastward at a phase speed of 0.24 m s${}^{-1}$. The phase speed increases with the planetary rotation rate and the vertical wavelength and also changes with the density scale height. Besides, the compressional beta-effect and the meridional vorticity tendency are reconstructed using reanalysis data and regressed upon tropical precipitation filtered for the Madden$-$Julian oscillation (MJO). The results suggest that the compressional beta-effect contributes 10.8% of the meridional vorticity budget associated with the MJO in terms of the ratio of the minimum values. The complete set of statically neutral equatorial waves may be significant in the interiors of stars and giant planets.

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H. Ong and P. Roundy
Mon, 4 May 20
10/55

Comments: 18 pages, 3 figures, submitted to J. Atmos. Sci. This paper originated as a course project of Hing Ong in ATM 523, Large Scale Dynamics of the Tropics, instructed by Paul Roundy. It became a chapter of Hing Ong’s PhD dissertation

Atmospheric dynamics on terrestrial planets with eccentric orbits [EPA]

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http://arxiv.org/abs/2004.14673


The insolation a planet receives from its parent star is the main engine of the climate and depends on the planet’s orbital configuration. Planets with non-zero obliquity and eccentricity will experience seasonal insolation variations. As a result, the climate will have a seasonal cycle, with its strength depending on the orbital configuration, and atmospheric characteristics. In this study, using an idealized general circulation model, we examine the climate response to changes in eccentricity for both zero and non-zero obliquity planets. In the zero obliquity case, a comparison between the seasonal response to changes in eccentricity and perpetual changes in the solar constant shows that the seasonal response strongly depends on the orbital period and radiative timescale. More specifically, using a simple energy balance model, we show the importance of the latitudinal structure of the radiative timescale in the climate response. We also show that the response strongly depends on the atmospheric moisture content. The combination of an eccentric orbit with non-zero obliquity is complex, as the insolation also depends on the perihelion position. Although the detailed response of the climate to variations in eccentricity, obliquity, and perihelion is involved, the circulation is constrained mainly by the thermal Rossby number and latitude of maximum temperature. Finally, we discuss the importance of different planetary parameters that affect the climate response to orbital configuration variations.

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I. Guendelman and Y. Kaspi
Fri, 1 May 20
5/54

Comments: N/A

The dependence of global super-rotation on planetary rotation rate [EPA]

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http://arxiv.org/abs/2004.08414


An atmosphere may be described as globally super-rotating if its total zonal angular momentum exceeds that associated with solid-body co-rotation with the underlying planet. In this paper, we discuss the dependence of global super-rotation in terrestrial atmospheres on planetary rotation rate. This dependence is revealed through analysis of global super-rotation in idealised General Circulation Model experiments with time-independent axisymmetric forcing, compared with estimates for global super-rotation in Solar System atmospheres. Axisymmetric and three-dimensional experiments are conducted. We find that the degree of global super-rotation in the three-dimensional experiments is closely related to that of the axisymmetric experiments, with some differences in detail. A scaling theory for global super-rotation in an axisymmetric atmosphere is derived from the Held-Hou model. At high rotation rate, our numerical experiments inhabit a regime where global super-rotation scales geostrophically, and we suggest that the Earth and Mars occupy this regime. At low rotation rate, our experiments occupy a regime determined by angular momentum conservation, where global super-rotation is independent of rotation rate. Global super-rotation in our experiments saturates at a value significantly lower than that achieved in the atmospheres of Venus and Titan, which instead occupy a regime where global super-rotation scales cyclostrophically. This regime can only be accessed when eddy induced up-gradient angular momentum transport is sufficiently large, which is not the case in our idealised numerical experiments. We suggest that the ‘default’ regime for a slowly rotating planet is the angular momentum conserving regime, characterised by mild global (and local) superrotation.

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N. Lewis, G. Colyer and P. Read
Tue, 21 Apr 20
17/90

Comments: Submitted to Journal of the Atmospheric Sciences. Comments welcome. This manuscript has not yet been peer reviewed

Aerosol characterization using satellite remote sensing of light pollution sources at night [IMA]

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http://arxiv.org/abs/2004.03467


A demanding challenge in atmospheric research is the night-time characterization of aerosols using passive techniques, that is, by extracting information from scattered light that has not been emitted by the observer. Satellite observations of artificial night-time lights have been used to retrieve some basic integral parameters, like the aerosol optical depth. However, a thorough analysis of the scattering processes allows one to obtain substantially more detailed information on aerosol properties. In this Letter we demonstrate a practicable approach for determining the aerosol particle size number distribution function in the air column, based on the measurement of the angular radiance distribution of the scattered light emitted by night-time lights of cities and towns, recorded from low Earth orbit. The method is self-calibrating and does not require the knowledge of the absolute city emissions. The input radiance data are readily available from several spaceborne platforms, like the VIIRS-DNB radiometer onboard the Suomi-NPP satellite.

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M. Kocifaj and S. Bará
Wed, 8 Apr 20
8/72

Comments: Author prepared version of a manuscript accepted for publication in Monthly Notices of the Royal Astronomical Society (Letter) 5 pages, 5 figures