The energy exchange mechanism in large-scale magnetic plasmoids collision [CL]

Recently, a super-elastic collision of large-scale plasmoids i.e. solar coronal mass ejections (CMEs) has been observed and further supported by numerical simulations. However, the energy gain by the system in the collision process is not clear. In-fact during plasmoids collision process, the energy exchange mechanism is still a chronic issue. Here, we present conclusive in situ evidence of sunward torsional Alfven waves in the magnetic cloud after the super-elastic collision of the largest plasmoids in the heliosphere. We conclude that magnetic reconnection and Alfven waves are the possible energy exchange mechanism during plasmoids interaction.

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A. Raghav and A. Kule
Tue, 17 Oct 17

Comments: 8 pg, 3 figures

Compressible magnetohydrodynamic turbulence in the Earth's magnetosheath: estimation of the energy cascade rate using in situ spacecraft data [CL]

The first estimation of the energy cascade rate ${|\epsilon_C|}$ of magnetosheath turbulence is obtained using the CLUSTER and THEMIS spacecraft data and an exact law of compressible isothermal magnetohydrodynamics turbulence. ${|\epsilon_C|}$ is found to be of the order of ${10{^{-13}} J.m^{3}.s^{-1}}$, at least three orders of magnitude larger than its value in the solar wind. Two types of turbulence are evidenced and shown to be dominated either by incompressible Alfv\’enic or magnetosonic-like fluctuations. Density fluctuations are shown to amplify the cascade rate and its spatial anisotropy in comparison with incompressible Alfv\’enic turbulence. Furthermore, for compressible magnetosonic fluctuations, large cascade rates are found to lie mostly near the linear kinetic instability of the mirror mode. New empirical power-laws are evidenced and relate ${|\epsilon_C|}$ to the turbulent Mach number and the internal energy. These new finding have potential applications in distant astrophysical plasmas that are not accessible to in situ measurements.

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L. Hadid, F. Sahraoui, S. Galtier, et. al.
Mon, 16 Oct 17

Comments: N/A

The detection of ultra-relativistic electrons in low Earth orbit [CL]

To better understand the radiation environment in low Earth orbit (LEO), the analysis of in-situ observations of a variety of particles, at different atmospheric heights, and in a wide range of energies, is needed. We present an analysis of energetic particles, indirectly detected by the Large Yield RAdiometer (LYRA) instrument on board ESA’s Project for On-board Autonomy 2 (PROBA2) satellite as background signal. Combining Energetic Particle Telescope (EPT) observations with LYRA data for an overlapping period of time, we identified these particles as electrons with an energy range of 2 to 8 MeV. The observed events are strongly correlated to geo-magnetic activity and appear even during modest disturbances. They are also well confined geographically within the L=4-6 McIlwain zone, which makes it possible to identify their source.

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A. Katsiyannis, M. Dominique, V. Pierrard, et. al.
Mon, 16 Oct 17

Comments: Topical Issue: Flares, CMEs and SEPs and their space weather impacts; 20 pages; 7 figures; Presented during 13th European Space Weather Week, 2016

Fully Kinetic Simulation of 3D Kinetic Alfven Turbulence [CL]

We present results from a fully kinetic, three-dimensional plasma turbulence simulation, resembling the typical plasma conditions found at kinetic scales of the solar wind. The spectral properties of the turbulence in the sub-ion range are consistent with theoretical expectations for kinetic Alfv\’ en waves. Furthermore, we calculate the scale-dependent anisotropy, defined by the relation $k_{\parallel}(k_{\perp})$, where $k_{\parallel}$ is a characteristic wavenumber along the local mean magnetic field at perpendicular scale $l_{\perp}\sim 1/k_{\perp}$. Over a limited range of sub-ion scales, the obtained scaling is close to $k_{\parallel}\propto k_{\perp}^{1/3}$, consistent with the standard analytical prediction for a critically balanced kinetic Alfv\’ en cascade. Our results compare favourably against a number of in-situ solar wind observations and demonstrate—from first principles—the feasibility of plasma turbulence models based on a critically balanced cascade of kinetic Alfv\’ en waves.

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D. Groselj, A. Mallet, N. Loureiro, et. al.
Wed, 11 Oct 17

Comments: submitted for publication

Insight into atmospheres of extrasolar planets through plasma processes [SSA]

Extrasolar planets appear in a chemical diversity unseen in our own solar system. Despite their atmospheres being cold, continuous and transient plasma processes do affect these atmosphere where clouds form with great efficiency. Clouds can be very dynamic due to winds for example in highly irradiated planets like HD 189733b, and lightning may emerge. Lightning, and discharge events in general, leave spectral fingerprints, for example due to the formation of HCN. During the interaction, lightning or other flash–ionisation events also change the electromagnetic field of a coherent, high energy emission which results a characteristic damping of the initial, unperturbed (e.g. cyclotron emission) radiation beam. We summarise this as ‘recipe for observers’. External ionisation by X-ray or UV e.g. from within the interstellar medium or from a white dwarf companion will introduce additional ionisation leading to the formation of a chromosphere. Signatures of plasma processes therefore allow for an alternative way to study atmospheres of extrasolar planets and brown dwarfs.

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C. Helling and I. Vorgul
Tue, 10 Oct 17

Comments: refereed proceeding (3 referees) for ‘Planetary Radio Emissions VIII’, Austrian Academy of Sciences Press

Pulsations in the Earth's Lower Ionosphere Synchronized with Solar Flare Emission [CL]

Solar flare emission at X-ray and extreme ultraviolet (EUV) energies can cause substantial enhancements in the electron density in the Earth’s lower ionosphere. It is now become clear that flares exhibit quasi-periodic pulsations with timescales of minutes at X-ray energies, but to date, it has not been known if the ionosphere is sensitive to this variability. Here, using a combination of Very Low Frequency (24 kHz) measurement together with space-based X-ray and EUV observations, we report pulsations of the ionospheric D-region, which are synchronized with a set of pulsating flare loops. Modeling of the ionosphere show that the D-region electron density varies by up to an order of magnitude over the timescale of the pulsations ($\sim$20 mins). Our results reveal that the Earth’s ionosphere is more sensitive to small-scale changes in solar soft X-ray flux than previously thought, and implies that planetary ionospheres are closely coupled to small-scale changes in solar/stellar activity.

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L. Hayes, P. Gallagher, J. McCauley, et. al.
Fri, 6 Oct 17

Comments: Accepted in JGR Space Physics

Mottled protoplanetary disk ionization by magnetically-channeled T Tauri star energetic particles [HEAP]

The evolution of protoplanetary disks is believed to be driven largely by angular momentum transport resulting from magnetized disk winds and turbulent viscosity. The ionization of the disk that is essential for these processes has been thought due to host star coronal X-rays but could also arise from energetic particles produced by coronal flares or by travelling shock waves and advected by the stellar wind. We have performed test-particle numerical simulations of energetic protons propagating into a realistic T~Tauri stellar wind, including a superposed small-scale magnetostatic turbulence. The isotropic (Kolmogorov power spectrum) turbulent component is synthesised along the individual particle trajectories. We have investigated the particle energy range, $[0.1 – 10]$ GeV, consistent with expectations from {\it Chandra} X-ray observations of large flares on T~Tauri stars and with recent indications by the {\it Herschel} Space Observatory of a significant contribution of energetic particles to the disk ionization of young stars. In contrast with a previous theoretical study finding dominance of energetic particle ionization over X-ray ionization throughout the disk, we find that the disk ionization is likely dominated by X-rays over much of its area except within narrow regions where the energetic particles are channeled onto the disk by the strongly-tangled and turbulent magnetic field lines. The radial thickness of such regions is $\sim 5$ stellar radii close to the star and broadens with increasing radial distance. In these regions, the disk ionization due to energetic particles can locally dominate the stellar X-ray contribution. This likely continues out to large distances from the star ($10$ AU or greater) where particles can be copiously advected and diffused by the turbulent wind.

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F. Fraschetti, J. Drake, O. Cohen, et. al.
Thu, 5 Oct 17

Comments: 16 pages, 12 figures, submitted