Global magnetospheric response to an interplanetary shock: THEMIS observations

Q.-G. Zong,V. Angelopoulos,D. Larson,J. P. McFadden,D. G. Sibeck,K.-H. Glassmeier,H. Zhang

doi:10.5194/angeo-30-379-2012

Abstract

Abstract. We investigate the global response of the geospace plasma environment to an interplanetary (IP) shock at ~02:24 UT on 28 May 2008 from multiple THEMIS spacecraft observations in the magnetosheath (THEMIS B and C), the mid-afternoon magnetosphere (THEMIS A), and the dusk magnetosphere (THEMIS D and E). The interaction of the transmitted IP shock with the magnetosphere has global effects. Consequently, it can affect geospace plasma significantly. After interacting with the bow shock, the IP shock transmitted a fast shock and a discontinuity which propagated through the magnetosheath toward the Earth at speeds of 301 km s−1 and 137 km s−1, respectively. THEMIS A observations indicate that the IP shock changed the properties of a plasmaspheric plume significantly. The plasmaspheric plume density increased rapidly from 10 to 100 cm−3 in 4 min and the ion distribution changed from an isotropic to a strongly anisotropic distribution. Electromagnetic ion cyclotron (EMIC) waves observed by THEMIS A are most likely excited by the anisotropic ion distributions caused by the IP shock impact. THEMIS A, but not D or E, observed a plasmaspheric plume in the dayside magnetosphere. Multiple spacecraft observations indicate that the dawn-side edge of the plasmaspheric plume was located between THEMIS A and D (or E).

Highlights

The interaction of interplanetary (IP) shocks with the magnetosphere includes several phases, including interaction with the bow shock, transmission through the magnetosheath, interaction with the magnetopause, transmission into the magnetosphere as fast and intermediate mode waves, modifications of the field-aligned and ionospheric current systems, and perturbations in ground magnetograms (Samsonov et al, 2007)
In MHD simulations, the interaction of an IP shock with the bow shock launches a fast shock into the magnetosheath and creates a new discontinuity (Zhuang et al, 1981) where the magnetic field strength and density increase, the temperature decreases and the velocity remains unchanged (Samsonov et al, 2006)
We investigate the global response of the geospace plasma environment to an IP shock from multiple THEMIS spacecraft observations in the magnetosheath (THEMIS B and C), the mid-afternoon magnetosphere (THEMIS A), and the dusk magnetosphere (THEMIS D and E)

Summary

Introduction

The interaction of interplanetary (IP) shocks (usually fast forward shocks) with the magnetosphere includes several phases, including interaction with the bow shock, transmission through the magnetosheath, interaction with the magnetopause, transmission into the magnetosphere as fast and intermediate mode waves, modifications of the field-aligned and ionospheric current systems, and perturbations in ground magnetograms (Samsonov et al, 2007). In MHD simulations, the interaction of an IP shock with the bow shock launches a fast shock into the magnetosheath and creates a new discontinuity (Zhuang et al, 1981) where the magnetic field strength and density increase, the temperature decreases and the velocity remains unchanged (Samsonov et al, 2006). Zhang et al.: Magnetospheric response to shock bow shock This rarefaction wave could result in outward bow shock motion. Based on results from global MHD simulations, Samsonov et al (2007) suggested that the dayside ionosphere reflects the transmitted fast shock and that the bow shock and the magnetopause move sunward when the reflected fast shock passes. Darrouzet et al (2008) presented a statistical analysis of the plasmaspheric plumes observed by the Cluster spacecraft.

Spacecraft observations

Conclusions