Large-scale current systems and ground magnetic disturbance during deep substorm injections

摘要

We present a detailed analysis of the large-scale current systems and their effects on theground magnetic field disturbance for an idealized substorm event simulated with theequilibrium version of the Rice Convection Model. The objective of this study is to evaluatehow well the bubble-injection picture can account for some classic features of thesubstorm expansion phase. The entropy depletion inside the bubble is intentionallydesigned to be so severe that it can penetrate deep into geosynchronous orbit. Theresults are summarized as follows: (1) Both the region-1-sense and region-2-sensefield-aligned currents (FACs) intensify substantially. The former resembles thesubstorm current wedge and flows along the eastern and western edges of the bubble.The latter is connected to the enhanced partial ring current in the magnetosphereassociated with a dipolarization front earthward of the bubble. In the ionosphere, thesetwo pairs of FACs are mostly interconnected via Pedersen currents. (2) The horizontalionospheric currents show a significant westward electrojet peaked at the equatorwardedge of the footprint of the bubble. The estimated ground magnetic disturbance isconsistent with the typical features at various locations relative to the center of the westwardelectrojet. (3) A prominent Harang-reversal-like boundary is seen in both ground DHdisturbance and plasma flow pattern, appearing in the westward portion of the equatorwardedge of the bubble footprint, with a latitudinal extent of 5 and a longitudinal extent of thehalf width of the bubble. (4) The dramatic dipolarization inside the bubble causes theionospheric map of the inner plasma sheet to exhibit a bulge-like structure, which may berelated to auroral poleward expansion. (5) The remarkable appearance of the westwardelectrojet, Harang-reversal-like boundary and poleward expansion starts when thebubble reaches the magnetic transition region from tail-like to dipole-likeconfiguration. We also estimate the horizontal and vertical currents using magnetograms attens of ground stations for a deep injection substorm event occurred on April 9, 2008,resulting in a picture that is qualitatively consistent with the simulation. Based on thesimulations and the observations, an overall picture of the ionospheric dynamics and itsmagnetospheric drivers during deep bubble injections is obtained.