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

Abstract

We 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 À97 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 V x B z > 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. IntroductionThe largest disturbances affecting the Earth's magnetosphere-ionosphere system are geomagnetic storms, primarily driven by the strong coupling of the interplanetary magnetic field (IMF) to the magnetospheric field. Storms can be caused either by a coronal mass ejection (CME), an immense expanding mass of plasma that erupts from the Sun and evolves into an interplanetary CME (ICME), or a corotating interaction region (CIR) forming at the leading edge of a high-speed stream (HSS) of plasma originating at coronal holes [Tsurutani et al., 1995]. The dynamic pressure sunward of an interplanetary shock suddenly compresses the Earth's magnetosphere. At the Earth's surface, this can be detected as a sudden impulse (SI+) or an increase in the horizontal component of the Earth's magnetic field. If southward interplanetary magnetic fields are present at or behind the shock (in either the sheath or the ICME proper), they will cause a magnetic storm through the process of magnetic reconnection with the Earth's magnetopause fields [Dungey, 1961]. If there are no southward IMFs, there will not be a magnetic storm. Joselyn and Tsurutani [1990] suggest that the shock compression be called an SI+, and the terms "SSC" and "initial phase" be dropped from usage. The storm onset will then be defined as the start of the storm main phase. CIR/HSS and CME events include complex combinations of pressure pulses and strong northward or southward magnetic fields. Corotating interaction regions form when solar wind streams with different velocities align in the radial direction. Density pileup occurs when a high-speed stream of the solar wind, emanating from polar coronal...

Multi-satellite observations of energy transport during an intense geomagnetic storm

“…A greater energy flux density first appeared in the dawndusk direction in the near-earth region than that of the midtail in the initial phase, which may be related to the many boundary perturbations, especially along the dawn flank and their effect on ion entry into the magnetosphere (Peroomian et al 2014). The stable energy flux density in the dawn-dusk direction in the tail was simultaneously observed by C1 and C3 in the dayside, which may indicate that direct and sufficient sources for the duskward energy consumption in the magnetotail are present.…”

“…Observations of the magnetic configuration and flow variations from two mid-tail probes THB (THEMIS B) and THC (THEMIS C) have been compared to results of a global scale MHD simulation of a storm driven by a co-rotating interaction region (CIR) and High Speed Stream (HSS) (Peroomian et al 2014). This MHD simulation shows that the arrival of the first CIR changes the configuration of the magnetotail and that the magnetic topology and flow structure of the magnetotail are never steady after a strong substorm.…”

The Source of Auroral Omegas

“…The state of the magnetotail during the MHD simulation of the magnetosphere on 9 March 2008 has been discussed in Peroomian et al. (2014). The MHD simulation results between 0623 UT and 0647 UT suggest that potentially both high speed flows and flow shears are responsible for the auroral omega bands observed in the ASIs between 0606 UT and 0631 UT.…”

Magnetospheric state of sawtooth events

“…As often shown in global magnetospheric simulations (e.g., see supporting information in Peroomian et al . []), the magnetosphere is constantly changing, such that it may be difficult to capture and characterize the instantaneous state of the magnetosphere.…”

“…Consequently, the magnetospheric configuration changes as it responds to the varying solar wind pressure and as the magnetospheric magnetic field interacts with the interplanetary field. As often shown in global magnetospheric simulations (e.g., see supporting information in Peroomian et al [2014]), the magnetosphere is constantly changing, such that it may be difficult to capture and characterize the instantaneous state of the magnetosphere.…”