The solar wind influences plasmasphere electron content

Abstract

MAGNETOSPHERIC plasma convection has been reviewed in detail by Axford1. A viscous-like interaction between plasma and magnetic field and magnetic-field-line merging have been suggested as mechanisms producing magnetospheric convection. In either model, convection is sustained by a dawn–dusk electric field (Econv) which has been shown2–4 to depend on solar-wind speed Vsw. Vasyliunas2 suggested a linear dependence, but Mendillo and Papagiannis3 estimated that the convection electric field varies nearly quadratically with solar wind speed—this conclusion was supported by Kivelson4. The convection field Econv and hence solar wind speed have important roles in determining the location of plasmaspause5,6. Model calculations assuming enhancement of the solar wind showed the plasmapause everywhere to be located at smaller L coordinates7 (L is the Mcllwain8 magnetic shell number). The location of the duskside bulge of the plasmapause has been shown to be inversely related to the solar wind speed3. The total plasmasphere electron content (NP) is supposed to increase with increase in L, the rate of increase being dependent on the density distribution assumed and the L values under consideration9. Thus one expects an increase in NP to be associated with a decrease in Vsw and vice versa. In this letter we give an experimental verification of this for two magnetic storms associated with large changes in Vsw, and for which NP and Vsw data are available. The results will prove useful in interpreting the disturbed time behaviour of NP.