Polar patches observed by ESR and their possible origin in the cusp region
Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identi®ed as possible candidates for polar-cap patches drifting anti-Sunward with the plasma ¯ow. Supporting m...
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.210.2142 http://www.ann-geophys.net/18/1043/2000/angeo-18-1043-2000.pdf |
| Summary: | Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identi®ed as possible candidates for polar-cap patches drifting anti-Sunward with the plasma ¯ow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles. Key words: Ionosphere �ionosphere±magnetosphere interactions; plasma temperature and density; polar ionosphere) 1Introduction Long-lived enhancements of ionospheric plasma, known as polar patches, drift in the anti-Sunward convection ¯ow across the polar cap. A comprehensive review of the current understanding of the patch phenomenon has been given by Crowley �1996). Patches occur predominantly under conditions of IMF Bz southward and drift across the polar cap at speeds of typically 300± 1000 ms)1 �Buchau et al., 1983). They have been observed in summer and winter �Buchau and Reinisch, 1991) and have been seen to form in geomagnetically |
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