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Can Enhanced Flux Loading by High‐Speed Jets Lead to a Substorm? Multipoint Detection of the Christmas Day Substorm Onset at 08:17 UT, 2015
Author(s) -
Nykyri K.,
Bengtson M.,
Angelopoulos V.,
Nishimura Y.,
Wing S.
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja026357
Subject(s) - substorm , magnetosheath , physics , geophysics , astrophysics , interplanetary magnetic field , solar wind , spacecraft , magnetopause , foreshock , flux (metallurgy) , field line , magnetohydrodynamic drive , magnetosphere , magnetohydrodynamics , magnetic field , geology , astronomy , seismology , materials science , quantum mechanics , aftershock , metallurgy
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 8:14 and location at x =−33 R 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 ≈08:17. All MMS spacecraft detected the same magnetosheath jet structure with B z =−25 nT at ∼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.