Inner magnetosphere currents during the CIR/HSS storm on July 21–23, 2009

Abstract

Modeling results of the configuration of the inner magnetosphere current systems, namely, the ring current and the near‐Earth tail current, during the July 21–23, 2009 CIR/HSS storm event are presented. We use two different modeling approaches, magnetic field modeling and particle modeling. We perform the magnetospheric magnetic field modeling with several standard and one modified Tsyganenko models, and the particle modeling with the Inner Magnetosphere Particle Transport and Acceleration Model (IMPTAM). It is found that the magnitudes of current densities in the inner magnetosphere computed with IMPTAM are comparable to those of computed with the TS05 magnetic field model. The model ring current, being asymmetric during the storm main phase did not show a duskward shift of its peak. It is shown with both modeling approaches that the incorporation of near‐Earth tail currents in the calculations of model Dst (SymH in the present paper) index is crucial, as there is significant current beyond 6.6 RE in the simulation results. A discrepancy is found between the SymH contributions from various currents as defined by the TS05 modules and from current streamline tracing through these same currents. We conclude that the method to calculate the contributions of different current systems to the model Dst using the global magnetospheric magnetic field models should be Biot‐Savart integration inside the regions, which contain the current systems, not using the magnetic field from the model representations of current modules.