Premium
The substorm current wedge: Further insights from MHD simulations
Author(s) -
Birn J.,
Hesse M.
Publication year - 2014
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2014ja019863
Subject(s) - substorm , physics , geophysics , current (fluid) , ionosphere , magnetohydrodynamics , wedge (geometry) , magnetosphere , field line , magnetohydrodynamic drive , equator , plasmoid , mechanics , magnetic field , computational physics , latitude , magnetic reconnection , optics , quantum mechanics , astronomy , thermodynamics
Abstract Using a recent magnetohydrodynamic simulation of magnetotail dynamics, we further investigate the buildup and evolution of the substorm current wedge (SCW), resulting from flow bursts generated by near‐tail reconnection. Each flow burst generates an individual current wedge, which includes the reduction of cross‐tail current and the diversion to region 1 (R1)‐type field‐aligned currents (earthward on the dawn and tailward on the duskside), connecting the tail with the ionosphere. Multiple flow bursts generate initially multiple SCW patterns, which at later times combine to a wider single SCW pattern. The standard SCW model is modified by the addition of several current loops, related to particular magnetic field changes: the increase of B z in a local equatorial region (dipolarization), the decrease of | B x |away from the equator (current disruption), and increases in | B y |resulting from azimuthally deflected flows. The associated loop currents are found to be of similar magnitude, 0.1–0.3 MA. The combined effect requires the addition of region 2 (R2)‐type currents closing in the near tail through dawnward currents but also connecting radially with the R1 currents. The current closure at the inner boundary, taken as a crude proxy of an idealized ionosphere, demonstrates westward currents as postulated in the original SCW picture as well as North‐South currents connecting R1‐ and R2‐type currents, which were larger than the westward currents by a factor of almost 2. However, this result should be applied with caution to the ionosphere because of our neglect of finite resistance and Hall effects.