An MHD simulation study of the dynamics of the 8–9 March 2008 CIR‐/HSS‐driven geomagnetic storm

Abstract

AbstractWe have carried out a global magnetohydrodynamic (MHD) simulation of a geomagnetic storm initiated by a corotating interaction region followed by a high‐speed solar wind (HSS) stream that occurred on 8–9 March 2008. The event began with the arrival of a corotating interaction region (CIR) at ~0720 UT on 8 March. The stream interface arrived at Earth at ~1830 UT on 8 March, and the arrival of a second density enhancement (a second CIR) at ~0140 UT on 9 March resulted in the main phase of the storm, with a peak Dst of −97 nT at 0600 UT on 9 March. Our MHD simulation of the event, spanning the interval of 0400 UT on 8 March to 0800 UT on 9 March, shows that the arrival of the first CIR changes the configuration of the magnetotail, and that after a strong substorm at ~1230 UT on 8 March, the tail evolves into a churning state in which the magnetic topology and flow structure of the magnetotail are never steady. In addition, we find that increases in ring current energy density show a nearly one‐to‐one correspondence to periods of VxBz > 0 (southward interplanetary magnetic field (IMF)). More importantly, we find that the ring current energy density in the MHD simulation shows a nearly linear response to increases in solar wind dynamic pressure, but only for the northward IMF intervals during the initial phase of the event, from 0400 UT to 1800 UT on 8 March.