Abstract
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.
Highlights
A typical sudden compression of the magnetosphere, caused by the encounter with the coronal mass ejection (CME), is associated with a world-wide enhancement of the northward ground magnetic field at low-latitudes with a slightly larger enhancement on the dayside
The other specific distinction of our approach is that we describe a peculiar situation when the interplanetary shock arrival is accompanied by the northward interplanetary magnetic field (IMF) rotation from the near horizontal direction
We consider a possible reason of the dawn-dusk asymmetry of the on-ground magnetic field created by the transition current system at low latitudes
Summary
For self-consistency we briefly describe here the transition current system model. It was shown (Clauer et al, 2001; Belenkaya et al, 2004) that the three-dimensional transition current system should form during a characteristic time period of tr ∼30−40 min after the magnetosphere encounters a CME-related shock containing a change from horizontal to northward IMF. Clauer et al (2001) calculated the magnetic field of the transition current system at the Earth’s equator at noon and midnight suggesting that the field-aligned currents at the open-closed field line boundary may be represented by two currents flowing to the ionosphere at dawn and out of the ionosphere at dusk. The Region 1 dawn current returns from the southern neutral point to the open field line boundary of the northern polar cap After that it flows as the Pedersen ionospheric current, and is closed by the NBZ field-aligned current flowing out from the northern ionosphere. The current circuit of the northern part of the transition current system located in the dawn-dusk plane for bx=0, by=0, and bz>0, becomes deformed under the action of the radial and azimuthal components of the northward IMF (see Fig. 3) This deformation creates a displacement of its magnetic field extrema. Comparison with our rough calculations (γ =3 h) gives a good agreement
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