Ion escape from Mars as a function of solar wind conditions: A statistical study
Ion escape from Mars as a function of solar wind conditions: A statistical study
复制标题
离子从火星逃逸与太阳风条件的关系：一项统计研究
DOI：
10.1016/j.icarus.2009.03.006
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发表时间：
2010
期刊：
影响因子：
3.2
通讯作者：
Y. Futaana
中科院分区：
文献类型：
--
作者：
H. Nilsson;E. Carlsson;D. Brain;M. Yamauchi;M. Holmström;S. Barabash;R. Lundin;Y. Futaana
利用火星快车（Mars Express）上的Aspera-3仪器获得的离子数据，结合火星全球勘测者（Mars Global Surveyor， MGS）航天器获得的太阳风代理数据，研究了太阳EUV和太阳风条件对火星离子逸出的影响。基于地球位置数据的太阳EUV通量代理，对火星进行了时间尺度的缩放和位移，用于研究与太阳EUV变率相关的较长时间尺度变化。数据为2004年5月至2005年11月。从离子数据中可以看出，从MGS测量推断出的亚太阳磁场强度明显依赖。太阳磁场强度越大，重离子流显著的区域被压缩，重离子通量密度越大。由于流出面积的差异，估计总流出量的差异略小于平均通量密度的差异。我们证实了先前的发现，逃逸的行星离子主要出现在太阳风电场指向的半球。这种效应在亚太阳磁场强的情况下更为明显。平均离子运动始终偏向太阳风电场方向，但主要运动方向是反太阳方向。反太阳流的速度随着向尾距离的增加而增加，在火星向下2到3个火星半径处，O+离子的速度达到100 km s - 1以上。不同的离子种类达到大致相同的体流能。我们没有发现太阳EUV通量与离子逸出分布或速率之间存在明显的相关性，可能是由于太阳EUV通量在我们研究区间内的变化幅度太小。结果表明，太阳风及其磁场直接与火星电离层相互作用，带走了更多的离子，从而获得了较高的亚太阳磁场强度。相互作用区和尾部重离子流区并没有完全屏蔽太阳风电场，太阳风电场会在相对较大的尾部距离上加速粒子。
The influence of solar EUV and solar wind conditions on ion escape at Mars is investigated using ion data from the Aspera-3 instrument on Mars Express, combined with solar wind proxy data obtained from the Mars Global Surveyor (MGS) spacecraft. A solar EUV flux proxy based on data from the Earth position, scaled and shifted in time for Mars, is used to study relatively long time scale changes related to solar EUV variability. Data from May 2004 until November 2005 has been used. A clear dependence on the strength of the subsolar magnetic field as inferred from MGS measurements is seen in the ion data. The region of significant heavy ion flows is compressed and the heavy ion flux density is higher for high subsolar magnetic field strength. Because of the difference in outflow area, the difference in estimated total outflow is somewhat less than the difference in average flux density. We confirm previous findings that escaping planetary ions are mainly seen in the hemisphere into which the solar wind electric field is pointed. The effect is more pronounced for the high subsolar magnetic field case. The average ion motion has a consistent bias towards the direction of the solar wind electric field, but the main motion is in the antisunward direction. The antisunward flow velocity increases with tailward distance, reaching above 100 km s−1at 2 to 3 martian radii downtail from Mars for O+ions. Different ion species reach approximately the same bulk flow energy. We did not find any clear correlation between the solar EUV flux and the ion escape distribution or rate, probably because the variation of the solar EUV flux over our study interval was too small. The results indicate that the solar wind and its magnetic field directly interacts with the ionosphere of Mars, removing more ions for high subsolar magnetic field strength. The interaction region and the tail heavy ion flow region are not perfectly shielded from the solar wind electric field, which accelerates particles over relatively large tail distances.