SM14B-05
MESSENGER Observations of Substorm Activity at Mercury

Monday, 14 December 2015: 16:52
2009 (Moscone West)
Wei-Jie Sun1, James A Slavin2, Suiyan Fu1, Jim M Raines3, Qiu-Gang Zong1, Gangkai Poh2, Xianzhe Jia2, Torbjorn Sundberg4, Daniel J Gershman5, Zuyin Pu6, Thomas Zurbuchen2 and Quanqi Shi7, (1)Peking University, School of Earth and Space Sciences, Beijing, China, (2)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (3)University of Michigan Ann Arbor, Department of Atmospheric, Oceanic and Space Sciences, Ann Arbor, MI, United States, (4)Queen Mary, University of London, London, E1, United Kingdom, (5)Oak Ridge Associated Universities, Oak Ridge, TN, United States, (6)Peking University, Beijing, China, (7)Shandong University at Weihai, Weihai, China
Abstract:
MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma measurements taken during crossings of Mercury's magnetotail from 2011 to 2014 have been investigated for substorms. A number of events with clear Earth-like growth phase and expansion phase signatures were found. The thinning of the plasma sheet and the increase of magnetic field intensity in the lobe were observed during the growth phase and plasma sheet was observed to thicken during the expansion phase, which are similar to the observations at Earth. But the time scale of Mercury’s substorm is only several minutes comparing with the several hours at Earth [Sun et al., 2015a]. Detailed analysis of magnetic field fluctuations during the substorm expansion phase have revealed low frequency plasma waves, e.g. Pi2-like pulsations. The By fluctuations accompanying substorm dipolarizations are consistent with pulses of field-aligned currents near the high latitude edge of the plasma sheet. Further study shows that they are near-circularly polarized electromagnetic waves, most likely Alfvén waves. Soon afterwards the plasma sheet thickened and MESSENGER detected a series of compressional waves. We have also discussed their possible sources [Sun et al., 2015b].

Sun, W.-J., J. A. Slavin, S. Y. Fu, et al. (2015a), MESSENGER observations of magnetospheric substorm activity in Mercury's near magnetotail. Geophys. Res. Lett., 42, 3692–3699. doi: 10.1002/2015GL064052.
Sun, W.-J., J. A. Slavin, S. Y. Fu, et al. (2015b), MESSENGER observations of Alfvénic and compressional waves during Mercury's substorms. Geophys. Res. Lett., 42, in press. doi: 10.1002/ 2015GL065452.

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