On the closure of the magnetospheric currents

A 3D model of the magnetospheric currents produced by the interaction of the magnetosphere-ionosphere (M-I) system with the solar wind (SW) is presented and studied. It is found that, at scale sizes between 80 km and 3 km at ionospheric altitudes, the magnetosphere tends to behave as a constant current source. Numerical simulation results show that the SW-M-I dynamo operates near short circuit current conditions for IMF Bz less than zero, and that the system therefore inefficiently converts the power available to the SW. Global magnetospheric instabilities can be avoided by an assumed perfect shielding approximation. This near-perfect shielding is discussed in terms of inertial currents or of shielding currents and discharge currents.