Interball 1/alpha 3 cold plasma measurements in the evening plasmasphere: Quite and disturbed magnetic conditions Original Research Article

Cold plasma fluxes measured by the ALPHA 3 instrument on INTERBALL 1 from July to October 1999, when the spacecraft crossed the dusk side outer plasmasphere are analyzed. The INTERBALL 1 orbit crosses the same flux tube on both sides of the magnetic equator at nearly the same height and most of the time cold ion spectra were very much alike. After a period of moderate geomagnetic activity similar isolated patches of dense plasma were observed during crossings of the same L-shell in southern and northern hemispheres at geomagnetic latitudes of ±20°. This suggests that filled magnetic flux tubes were located above almost empty tubes.The interrelationships between cold plasma parameters at a given L-shell and geomagnetic activity, and the external solar wind flow, were analyzed. A tendency for enhanced cold H+ ion temperatures inside the dusk plasmasphere in magnetically disturbed periods is found. The cold ion density in the dusk side plasmasphere increases with the solar wind dynamic pressure.