The Penetration of Interplanetary Magnetic and Electric Fields into the Magnetosphere

Abstract

The influence of the interplanetary magnetic field on solar wind-magnetosphere interactions is described. A finite-conductivity solution for the magnetic field B in the magnetosheath is constructed, and it holds even close to the magnetopause, where the frozen-flux approximation is invalid. The electric field E implied by the solar wind plasma bulk motion is determined, too. Magnetic field diffusion caused by finite conductivity results in only a partial screening of the outer field in a dissipative layer near the magnetopause, with residual B_n and E_t penetrating into the magnetosphere. The dependence of the magnetic and electric fields at the magnetopause on the magnetic Reynolds number, R_m, is B_n-R_m^-p and E_t-R_m^-p; B_t-R_m^p, and E_n-R_m^p where p=0.25. The Poynting vector flux over the magnetopause is independent of R_m and equal to -2.6×10¹¹W for usual solar wind and IMF parameters. Assuming E₁₁=0 on open magnetic field lines, it is possible to determine the electric field within the region of open magnetic field lines using IMF-dependent boundary conditions at the magnetopause. Field-aligned currents in this region (or in the polar cap) are derived from the equation Div (ΣE)=j₁₁, where the ionospheric conductivity Σ is assumed uniform. Sunward convection for northward IMF is explained. A shift of the cusp projection in the ionosphere due to the IMF effect is presented. For northward IMF a two-vortex convection pattern in the polar cap is obtained. Comparison of model predictions with experimental data shows good agreement in the dayside polar cap. The proposed model provides a self-consistent analytic solution of the problem of IMF penetration into the magnetosphere.