Properties of a large-scale flux rope and current sheet region on the dayside of Mars: MGS MAG/ER and MEX ASPERA-3 ELS observations
Properties of a large-scale flux rope and current sheet region on the dayside of Mars: MGS MAG/ER and MEX ASPERA-3 ELS observations
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DOI：
10.1016/j.icarus.2014.08.019
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发表时间：
2014-11
期刊：
影响因子：
3.2
通讯作者：
Y. Soobiah;J. Wild;M. Beharrell;S. Barabash;R. Lillis;D. Mitchell;A. Coates;J. Winningham;
中科院分区：
文献类型：
--
作者：
Y. Soobiah;J. Wild;M. Beharrell;S. Barabash;R. Lillis;D. Mitchell;A. Coates;J. Winningham;
我们介绍了MGS MAG/ER和MEX ASPERA-3 ELS对火星日侧大尺度磁通量绳的双重航天器观测，该磁通量绳靠近地壳磁场和日侧电流片区域。当电离层中覆盖的太阳风磁场具有+ by分量（在MSO中）时，在重复的MGS轨道上观察到电流片（包括大尺度通量绳）。对大尺度磁通绳和其后两次电流片交叉的最小方差分析（MVA）表明，磁场沿中间方差方向有一个共同的峰值，表明重连电流片的法向分量。所有的重复轨道都证明了等离子体边界的证据，当进入由地壳磁场主导的区域时，电子差通量在100 eV以上减少，并且与测量的磁场强度是未受干扰的地壳磁场的两倍相吻合。我们认为，这形成了地壳磁场和覆盖的太阳风磁场（来自电离层或磁鞘）之间磁重联的证据，这些磁场位于火星白天侧的“迷你磁层顶”类型边界。在大尺度磁通绳、电流片交叉和径向地壳磁场区域中观察到的相似的电子俯角分布表明，这些区域具有共同的磁场拓扑结构，可以在火星白天的开放地壳磁场中捕获磁鞘粒子。因此，表明在磁重联x线区域或开放的地壳磁场与相反方向的太阳风磁场相遇的地方存在捕获四极磁场。在电离层中覆盖的太阳风磁场强度较弱的时候，在2000公里的延伸区域内观察到电流片交叉。扩展的电流片展示了热抗磁区域的特性和镜像模式结构或磁孔的特征，这是首次在火星电离层中发现这种结构。观测结果表明，低能电子可以通过垂直加热/俯仰角扩散的局部过程加速，并支持Nykyri等人（Nykyri等人[2012]）在地球极尖处报告的类似结果。j .大气压。Sol-Terr。物理学报，87,70)。这种大规模的高能结构通常与行星电离层以外的区域有关，而火星电离层内的发生可能对逃逸过程和火星大气的演化产生重要影响。
We present dual spacecraft observations by MGS MAG/ER and MEX ASPERA-3 ELS of a large-scale magnetic flux rope on the dayside of Mars that occurs in close proximity to the crustal magnetic fields and a dayside current sheet region. A current sheet (including the large-scale flux rope) was observed on repeated MGS orbits when the draped solar wind magnetic field present in the ionosphere had a+ B y component (in MSO). Minimum Variance Analysis (MVA) of the large-scale flux rope and two current sheet crossings that occur after show a common peak in magnetic field along the intermediate variance direction, indicating the normal component of a reconnecting current sheet. All repeated orbits demonstrated evidence of a plasma boundary by the decrease in electron differential flux above 100 eV when moving into regions dominated by the crustal magnetic field, and coincided with the measured magnetic field strength being double the undisturbed crustal magnetic field. We argue this forms evidence of magnetic reconnection between crustal magnetic fields and draped solar wind magnetic field (from ionosphere or magnetosheath) at a “mini-magnetopause” type boundary on the dayside of Mars. Similar electron pitch angle distributions observed during the large-scale flux rope, current sheet crossings, and regions of radial crustal magnetic field, suggest these regions share a common magnetic field topology for the trapping of magnetosheath particles on open crustal magnetic fields on the dayside of Mars. As such, indicates a trapping quadrupole magnetic field exist either at the magnetic reconnection X-line region or where open crustal magnetic fields meet oppositely directed solar wind magnetic field. At a time when the draped solar wind magnetic field present in the ionosphere was weaker in strength, the current sheet crossing was observed over an extended region of 2000 km. The extended current sheet demonstrated properties of a hot diamagnetic region and features of a mirror mode structure or magnetic hole, the first time such a structure has been found in the ionosphere of Mars. Observations suggests lower energy electrons could be accelerated by a local process of perpendicular heating/pitch angle diffusion and supports similar results at the Earth’s polar cusp reported by Nykyri et al.(Nykyri et al.[2012]. J. Atmos. Sol-Terr. Phys. 87, 70). Such large scale and energetic structures are usually associated with regions beyond a planet’s ionosphere, and the occurrence within the ionosphere of Mars may have an important impact on escape processes and the evolution of the martian atmosphere.