关键词：
substorm onset
high‐speed jets
magnetotail tail reconnection
Pi2 pulsations
auroral brightening
plasmoid
摘要：
This paper describes highly interesting observations of the 25 December 2015 substorm onset at 08:17 UT during northward interplanetary magnetic field (IMF) while magnetosheath contained several intervals of negative B-z. A unique alignment of several spacecraft near the Earth-Sun line together with magnetohydrodynamic simulations, ground-based magnetometer, and auroral observations allow a comprehensive timing analysis of the events leading to substorm onset. Perplexingly, prior to substorm onset Geotail measured for 26 min positive IMF B-z just upstream of the bow shock, while simultaneously MMS spacecraft measured several intervals of strong negative B-z in the dayside magnetosheath. These strong pulses of negative B-z in the magnetosheath were associated with high dynamic pressure magnetosheath jets, likely created by foreshock transients during strongly radial IMF interval. Multipoint plasma and magnetic field measurements from ARTEMIS and THEMIS spacecraft were used to determine tail reconnection time at approximate to 8:14 and location at x = -33R(E). Ground-based observations of Pi2 pulsations and auroral brightening, with observations of a dipolarization front by THEMIS spacecraft, allowed determination of substorm onset to be at approximate to 08:17. All MMS spacecraft detected the same magnetosheath jet structure with B-z = -25 nT at similar to 08:00 while IMF was northward. Based on DMSP observations and timing analysis we propose that these jets produced magnetopause reconnection leading to final, critical flux enhancement in the midtail region, which may have triggered reconnection 12-14 min later after jet observations.
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详细信息
Wiley期刊
