Premium
Three‐Step Buildup of the 17 March 2015 Storm Ring Current: Implication for the Cause of the Unexpected Storm Intensification
Author(s) -
Keika Kunihiro,
Seki Kanako,
Nosé Masahito,
Miyoshi Yoshizumi,
Lanzerotti Louis J.,
Mitchell Donald G.,
Gkioulidou Matina,
Manweiler Jerry W.
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2017ja024462
Subject(s) - ring current , plasma sheet , storm , population , magnetosphere , solar wind , geomagnetic storm , penetration (warfare) , current sheet , plasma , spectral index , geophysics , atmospheric sciences , physics , meteorology , spectral line , magnetohydrodynamics , astronomy , demography , nuclear physics , operations research , sociology , engineering
We examine the spatiotemporal variations of the energy density and the energy spectral evolution of energetic ions in the inner magnetosphere during the main phase of the 17 March 2015 storm, using data from the RBSPICE and EMFISIS instruments onboard Van Allen Probes. The storm developed in response to two southward IMF intervals separated by about 3 h. In contrast to two steps seen in the Dst /SYM‐H index, the ring current ion population evolved in three steps: the first subphase was apparently caused by the earlier southward IMF, and the subsequent subphases occurred during the later southward IMF period. Ion energy ranges that contribute to the ring current differed between the three subphases. We suggest that the spectral evolution resulted from the penetration of different plasma sheet populations. The ring current buildup during the first subphase was caused by the penetration of a relatively low‐energy population that had existed in the plasma sheet during a prolonged prestorm northward IMF interval. The deeper penetration of the lower‐energy population was responsible for the second subphase. The third subphase, where the storm was unexpectedly intensified to a Dst /SYM‐H level of <−200 nT, was caused by the penetration of a hot, dense plasma sheet population. We attribute the hot, dense population to the entry of hot, dense solar wind into the plasma sheet and/or ion heating/acceleration in the near‐Earth plasma sheet associated with magnetotail activity such as reconnection and dipolarization.