Abstract
During strong geomagnetic disturbances, the Earth’s magnetosphere exhibits unusual and nonlinear interaction with the incident flow of magnetized solar wind plasma. Global Magneto-hydro-dynamic (MHD) modeling of the magnetosphere predicts that the storm-time effects at the magnetopause result from the abnormal plasma transport and/or extremely strong field aligned currents. In-situ observations of the magnetospheric boundary, magnetopause, by Geosynchronous Operational Environmental Satellite (GOES) allowed us to find experimentally such effects as a saturation of the dayside reconnection, unusual bluntness and prominent duskward skewing of the nose magnetopause. The saturation and duskward skewing were attributed to the storm-time magnetopause formation under strong southward interplanetary magnetic field (IMF). The unusual bluntness was observed during both high solar wind pressure and strong southward IMF. We suggest that these phenomena are caused by a substantial contribution of the cross-tail current magnetic field and the hot magnetospheric plasma from the asymmetrical ring current into the pressure balance at the dayside magnetopause.
Highlights
The magnetopause shape is usually represented by a surface of revolution around the aberrated Sun-Earth line, or X-GSM axis
It was derived by Suvorova et al (2005) on the basis of 23 magnetopause crossings observed by 7 geosynchronous satellites during 18 storm events and using solar wind data provided by 3 different upstream monitors
We find that during intense reconnection at the magnetopause affected by very strong southward interplanetary magnetic field (IMF), the magnetopause in the postnoon sector is characterized by a prominent bluntness, the extent is estimated to be from 0° to ~30° in longitude and from ~-10° to ~10° in latitude
Summary
The magnetopause shape is usually represented by a surface of revolution around the aberrated Sun-Earth line, or X-GSM axis. The magnetopause exhibits unusual and nonlinear behavior such as reconnection saturation and prominent dawn-dusk asymmetry (e.g., Dmitriev et al 2004, 2011; Suvorova et al 2005). Based on statistical analysis of magnetopause crossings of geosynchronous satellites, Suvorova et al (2003) proposed that the reconnection saturation is caused by an enhanced thermal pressure of the magnetospheric plasma and ring current particles during strong magnetic storms. The partial ring current includes a westward azimuthal current at low latitudes, closed via field-aligned currents and localized in the evening-premidnight sector This component is quite important in the modeling of the storm-time magnetosphere since it provides the observed strong dawn-dusk asymmetry of the geomagnetic field, extending over a wide range of altitudes up to geosynchronous orbit.
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