Field‐aligned current distribution in the transition current system

Abstract

The interactions of coronal mass ejections with the Earth's magnetosphere are interesting because they often lead to extreme forcing of magnetospheric convection. Here we consider the initial interaction of a CME with the magnetosphere for the specific case in which there is a sharp increase in the dynamic pressure (interplanetary shock) that is associated with a simultaneous northward turning of the interplanetary magnetic field (IMF). The magnetospheric response to such conditions has been observed to be atypical to that expected for the compression of the magnetosphere. The sudden magnetic field increase observed at low‐latitude ground stations in response to such an event is asymmetric, with the largest field enhancement observed on the nightside and little or no field increase observed near local noon. We explain this response in terms of a temporary transition current system that is generated in the high‐latitude magnetosphere in response to the northward turning of the IMF. In this paper we consider the dependence of the distribution of field‐aligned currents in the transition current system to the radial and azimuthal components of the IMF. Model results are compared with the onground magnetometer data during 31 March 2001 storm sudden commencement (SSC).