MESSENGER Observations of Disappearing Dayside Magnetosphere Events at Mercury
MESSENGER Observations of Disappearing Dayside Magnetosphere Events at Mercury
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DOI：
10.1029/2019ja026892
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发表时间：
2019-08
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影响因子：
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通讯作者：
J. Slavin;H. R. Middleton;J. Raines;X. Jia;J. Zhong;Weijie Sun;S. Livi;S. Imber;G. Poh;M. Akhavan-Tafti;J. Jasinski;G. DiBraccio;Chuanfei Dong;R. Dewey;M. L. Mays
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作者：
J. Slavin;H. R. Middleton;J. Raines;X. Jia;J. Zhong;Weijie Sun;S. Livi;S. Imber;G. Poh;M. Akhavan-Tafti;J. Jasinski;G. DiBraccio;Chuanfei Dong;R. Dewey;M. L. Mays
在飞越水星昼侧半球期间进行的水星表面、空间环境、地球化学和测距 (MESSENGER) 测量表明，尽管航天器达到了 300 公里以下的高度，但有四次航天器仍然处于磁鞘中。在这些消失的日侧磁层 (DDM) 事件中，航天器直到处于非常高的磁纬度（约 66 至 80°）时才遇到磁层顶。这些 DDM 事件因其极高的太阳风动态压力（Psw ~140 至 290 nPa）和强烈的南向磁场（Bz ~ -100 至 -400 nT（在磁鞘中测量）而脱颖而出。此外，在这些事件期间，在非常接近地表的地方观测到弓形激波，高度约为 1,200 公里。有人认为，与日冕物质抛射密切相关的 DDM 事件是由于太阳风压缩和/或重新连接驱动的日侧磁层侵蚀所致。这些事件期间弓形激波的高度非常低，强烈表明太阳风在这些事件期间影响了水星阳光照射的半球的大部分区域。需要对这些消失的白天事件进行更多研究，但在这些时间间隔内，太阳风从地表溅射到外逸层的中性粒子可能会最大化。
MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) measurements taken during passes over Mercury's dayside hemisphere indicate that on four occasions the spacecraft remained in the magnetosheath even though it reached altitudes below 300 km. During these disappearing dayside magnetosphere (DDM) events, the spacecraft did not encounter the magnetopause until it was at very high magnetic latitudes, ~66 to 80°. These DDM events stand out with respect to their extremely high solar wind dynamic pressures, Psw ~140 to 290 nPa, and intense southward magnetic fields, Bz ~ −100 to −400 nT, measured in the magnetosheath. In addition, the bow shock was observed very close to the surface during these events with a subsolar altitude of ~1,200 km. It is suggested that DDM events, which are closely associated with coronal mass ejections, are due to solar wind compression and/or reconnection‐driven erosion of the dayside magnetosphere. The very low altitude of the bow shock during these events strongly suggests that the solar wind impacts much of Mercury's sunlit hemisphere during these events. More study of these disappearing dayside events is required, but it is likely that solar wind sputtering of neutrals from the surface into the exosphere maximizes during these intervals.