Magnetic field of the transition current system: dawn-dusk asymmetry

Abstract. In this paper we consider the interactions of coronal mass ejections (CMEs) with the Earth's 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) from the near horizontal direction. Previously, we have shown that under such circumstances, the so-called transition current systems arise. These temporary high-latitude current systems create a low-latitude asymmetric magnetic field on the ground with a large northward field enhancement on the nightside and little or no field increase near local noon. Here we investigate the dawn-dusk asymmetry of the low-latitude on-ground magnetic field of the transition current system caused by the IMF. Analysis of the Region 1 current circuit for northward IMF shows a change in its shape controlled by different IMF components. Due to this geometrical effect, the maximum and minimum magnetic field disturbances appear to be shifted. The obtained results supplement and define more precisely the locations of the magnetic disturbance extrema retrieved recently by Clauer et al. (2001). The results of this study are compared with the available observations. A good accordance is demonstrated.