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Electron dynamics near diamagnetic regions of comet 67P/Churyumov- Gerasimenko
Planetary and Space Science ( IF 1.8 ) Pub Date : 2020-08-01 , DOI: 10.1016/j.pss.2020.104924
H. Madanian , J.L. Burch , A.I. Eriksson , T.E. Cravens , M. Galand , E. Vigren , R. Goldstein , Z. Nemeth , P. Mokashi , I. Richter , M. Rubin

Abstract The Rosetta spacecraft detected transient and sporadic diamagnetic regions around comet 67P/Churyumov-Gerasimenko. In this paper we present a statistical analysis of bulk and suprathermal electron dynamics, as well as a case study of suprathermal electron pitch angle distributions (PADs) near a diamagnetic region. Bulk electron densities are correlated with the local neutral density and we find a distinct enhancement in electron densities measured over the southern latitudes of the comet. Flux of suprathermal electrons with energies between tens of eV to a couple of hundred eV decreases each time the spacecraft enters a diamagnetic region. We propose a mechanism in which this reduction can be explained by solar wind electrons that are tied to the magnetic field and after having been transported adiabatically in a decaying magnetic field environment, have limited access to the diamagnetic regions. Our analysis shows that suprathermal electron PADs evolve from an almost isotropic outside the diamagnetic cavity to a field-aligned distribution near the boundary. Electron transport becomes chaotic and non-adiabatic when electron gyroradius becomes comparable to the size of the magnetic field line curvature, which determines the upper energy limit of the flux variation. This study is based on Rosetta observations at around 200 ​km cometocentric distance when the comet was at 1.24 AU from the Sun and during the southern summer cometary season.

中文翻译:

彗星 67P/Churyumov-Gerasimenko 抗磁区附近的电子动力学

摘要 Rosetta 探测器探测到 67P/Churyumov-Gerasimenko 彗星周围的瞬态和零星抗磁区域。在本文中,我们介绍了体积和超热电子动力学的统计分析,以及抗磁区域附近超热电子俯仰角分布 (PAD) 的案例研究。体电子密度与局部中性密度相关,我们发现在彗星南纬测量的电子密度明显增强。每当航天器进入抗磁区域时,能量在几十 eV 到几百 eV 之间的超热电子的通量就会减少。我们提出了一种机制,其中这种减少可以通过与磁场相关的太阳风电子来解释,并且在衰减的磁场环境中绝热传输后,进入抗磁区域的机会有限。我们的分析表明,超热电子 PAD 从抗磁腔外几乎各向同性的分布演变为边界附近的场对齐分布。当电子回旋半径变得与磁力线曲率的大小相当时,电子传输变得混乱和非绝热,这决定了通量变化的能量上限。这项研究基于罗塞塔观测,当时彗星距离太阳 1.24 天文单位,并且在南部夏季彗星季节期间,彗心距离约为 200 公里。进入抗磁区域的机会有限。我们的分析表明,超热电子 PAD 从抗磁腔外几乎各向同性的分布演变为边界附近的场对齐分布。当电子回旋半径变得与磁力线曲率的大小相当时,电子传输变得混乱和非绝热,这决定了通量变化的能量上限。这项研究基于罗塞塔观测,当时彗星距离太阳 1.24 天文单位,并且在南部夏季彗星季节期间,彗心距离约为 200 公里。进入抗磁区域的机会有限。我们的分析表明,超热电子 PAD 从抗磁腔外几乎各向同性的分布演变为边界附近的场对齐分布。当电子回旋半径变得与磁力线曲率的大小相当时,电子传输变得混乱和非绝热,这决定了通量变化的能量上限。这项研究基于罗塞塔观测,当时彗星距离太阳 1.24 天文单位,并且在南部夏季彗星季节期间,彗心距离约为 200 公里。当电子回旋半径变得与磁力线曲率的大小相当时,电子传输变得混乱和非绝热,这决定了通量变化的能量上限。这项研究基于罗塞塔观测,当时彗星距离太阳 1.24 天文单位,并且在南部夏季彗星季节期间,彗心距离约为 200 公里。当电子回旋半径变得与磁力线曲率的大小相当时,电子传输变得混乱和非绝热,这决定了通量变化的能量上限。这项研究基于罗塞塔观测,当时彗星距离太阳 1.24 天文单位,并且在南部夏季彗星季节期间,彗心距离约为 200 公里。
更新日期:2020-08-01
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