Space Climate and Space Weather over the past 400 years: 1. The Power input to the Magnetosphere [CL]

Using information on geomagnetic activity, sunspot numbers and cosmogenic isotopes, supported by historic eclipse images and in conjunction with models, it has been possible to reconstruct annual means of solar wind speed and number density and heliospheric magnetic field (HMF) intensity since 1611, when telescopic observations of sunspots began. These models are developed and tuned using data recorded by near-Earth interplanetary spacecraft and by solar magnetograms over the past 53 years. In this paper, we use these reconstructions to quantify power input into the magnetosphere over the past 400 years. For each year, both the annual mean power input is computed and its distribution in daily means. This is possible because the distribution of daily values divided by the annual mean is shown to maintain the same lognormal form with a constant variance. This study is another important step towards the development of a physics-based, long-term climatology of space weather conditions.

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M. Lockwood, M. Owens, L. Barnard, et. al.
Thu, 17 Aug 17

Comments: In press, accepted for publication by J. Space Weather Space Clim. Ms# swsc170035 (accepted version, 28 pages, 2 Tables, 12 Figures)

A Review of the 0.1 Reconnection Rate Problem [CL]

A long-standing problem in magnetic reconnection is to explain why it tends to proceed at or below a normalized rate of 0.1. This article gives a review of observational and numerical evidence for this rate and discusses recent theoretical work addressing this problem. Some remaining open questions are summarized.

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P. Cassak, Y. Liu and M. Shay
Mon, 14 Aug 17

Comments: 16 pages, 4 figures, the manuscript was prepared for the first Journal of Plasma Physics Frontiers in Plasma Physics Conference, accepted to Journal of Plasma Physics, August 2017

The Andromeda Study: A Femto-Spacecraft Mission to Alpha Centauri [IMA]

This paper discusses the physics, engineering and mission architecture relating to a gram-sized interstellar probe propelled by a laser beam. The objectives are to design a fly-by mission to Alpha Centauri with a total mission duration of 50 years travelling at a cruise speed of 0.1c. Furthermore, optical data from the target star system is to be obtained and sent back to the Solar system. The main challenges of such a mission are presented and possible solutions proposed. The results show that by extrapolating from currently existing technology, such a mission would be feasible. The total mass of the proposed spacecraft is 23g and the space-based laser infrastructure has a beam power output of 15GW. Rurther exploration of the laser – spacecraft tradespace and associated technologies are necessary.

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A. Hein, K. Long, D. Fries, et. al.
Mon, 14 Aug 17

Comments: N/A

Did the 2000 November 8 solar flare accelerate protons to >=40 GeV? [SSA]

It has been reported that a 5.7sigma directional muon excess coincident with the 2000 July 14 solar flare was registered by the L3 precision muon spectrometer [Ruiguang Wang, Astroparticle Phys., 31(2009) 149]. Using a same analysis method and similar criteria of event selection, we have analyzed the L3 precision muon spectrometer data during November 2000. The result shows that a 4.7sigma muon excess appeared at a time coincident with the solar flare of 8 of November 2000. This muon excess corresponds to above 40 GeV primary protons which came from a sky cell of solid angle 0.048 sr. The probability of being a background fluctuation is estimated to be about 0.1%. It has been convinced that solar protons could be accelerated to tens of GeV in those Class X solar flares which usually arose solar cosmic ray ground level enhancement (GLE) events. However, whether a Class M solar flare like the non-GLE event of 8 November 2000 may also accelerate solar protons to such high energies? It is interesting and noteworthy.

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R. Wang, L. Ding, Y. Ma, et. al.
Wed, 9 Aug 17

Comments: N/A

Records of Auroral Candidates and Sunspots in Rikkokushi, Chronicles of Ancient Japan from Early 7th Century to 887 [SSA]

In this article, we present the results of the surveys on sunspots and auroral candidates in Rikkokushi, Japanese Official Histories from the early 7th century to 887 to review the solar and auroral activities. In total, we found one sunspot record and 13 auroral candidates in Rikkokushi. We then examine the records of the sunspots and auroral candidates, compare the auroral candidates with the lunar phase to estimate the reliability of the auroral candidates, and compare the records of the sunspots and auroral candidates with the contemporary total solar irradiance reconstructed from radioisotope data. We also identify the locations of the observational sites to review possible equatorward expansion of auroral oval. These discussions suggest a major gap of auroral candidates from the late 7th to early 9th century, which includes the minimum number of candidates reconstructed from the radioisotope data, a similar tendency as the distributions of sunspot records in contemporary China, and a relatively high magnetic latitude with a higher potential for observing aurorae more frequently than at present.

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H. Hayakawa, K. Iwahashi, H. Tamazawa, et. al.
Fri, 4 Aug 17

Comments: 2017/08/02 accepted for publication in PASJ

Spatially Localized Particle Energization by Landau Damping in Current Sheets Produced by Strong Alfven Wave Collisions [CL]

Understanding the removal of energy from turbulent fluctuations in a magnetized plasma and the consequent energization of the constituent plasma particles is a major goal of heliophysics and astrophysics. Previous work has shown that nonlinear interactions among counterpropagating Alfven waves—or Alfven wave collisions—are the fundamental building block of astrophysical plasma turbulence and naturally generate current sheets in the strongly nonlinear limit. A nonlinear gyrokinetic simulation of a strong Alfven wave collision is used to examine the damping of the electromagnetic fluctuations and the associated energization of particles that occurs in self-consistently generated current sheets. A simple model explains the flow of energy due to the collisionless damping and the associated particle energization, as well as the subsequent thermalization of the particle energy by collisions. The net particle energization by the parallel electric field is shown to be spatially intermittent, and the nonlinear evolution is essential in enabling that spatial non-uniformity. Using the recently developed field-particle correlation technique, we show that particles resonant with the Alfven waves in the simulation dominate the energy transfer, demonstrating conclusively that Landau damping plays a key role in the spatially intermittent damping of the electromagnetic fluctuations and consequent energization of the particles in this strongly nonlinear simulation.

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G. Howes, A. McCubbin and K. Klein
Thu, 3 Aug 17

Comments: 34 pages, 17 figures, submitted to Journal of Plasma Physics

Interplay between Alfvén and magnetosonic waves in compressible magnetohydrodynamics turbulence [CL]

Using spatio-temporal spectra we show direct evidence of excitation of magnetosonic and Alfv\’en waves in three-dimensional compressible magnetohydrodynamic turbulence at small Mach numbers. For the plasma pressure dominated regime, or high $\beta$ regime (with $\beta$ the ratio between fluid and magnetic pressure), and for the magnetic pressure dominated regime, or low $\beta$ regime, we study magnetic field fluctuations parallel and perpendicular to a guide magnetic field $\textbf{B}_0$. In the low $\beta$ case we find excitation of compressible and incompressible fluctuations, with a transfer of energy towards Alfv\’enic modes and to a lesser extent towards magnetosonic modes. In particular, we find signatures of the presence of fast magnetosonic waves in a scenario compatible with that of weak turbulence. In the high $\beta$ case, fast and slow magnetosonic waves are present, with no clear trace of Alfv\’en waves, and a significant part of the energy is carried by two-dimensional turbulent eddies.

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N. Andres, P. Leoni, P. Mininni, et. al.
Mon, 31 Jul 17

Comments: N/A