ABSTRACT
The simplest mathematically closed set of equations that yield realistic solutions of global magnetospheric configurations varying with the solar wind conditions is based on the equations of ideal MHD. Both overshielding and undershielding result in an appearance of magnetospherically generated electric fields in the inner magnetosphere and ionosphere called prompt penetration electric fields. Penetration electric fields are an important factor for space weather. The sustained driving of enhanced convection during magnetic storms not only leads to penetration of electric fields to the innermost region of the magnetosphere, but also causes intensification of auroral electrojets and other ionospheric horizontal currents. It is difficult to construct an empirical model of the magnetospheric electric field pattern, as electric fields measured close to the equatorial plane often include significant inductive component. The empirical model of Weimer is probably the most widely use parameterized representation of the ionospheric convection electrostatic potential.
