A NUMERICAL IONOSPHERE-MAGNETOSPHERE COUPLING MODEL WITH VARIABLE CONDUCTIVITIES

We describe a numerical ionosphere-magnetosphere coupling model with a relationship between the field-aligned potential drop and the ionosph eric conductivities. A two-dimensional incompressible magnetohydrodyna mic (MHD) model for the magnetosphere, field lines with finite resisti vity, a ''2 1/2'' dimensional ionosphere, as well as a phenomenologica l modeling of the ionization process are integrated in a time-dependen t fluid simulation code. We discuss the algorithm and the validity of the results and give an example run with possible application to eastw ard drifting OMEGA bands of the morning sector. Our model is valid for time scales longer than the Alfven bounce time and for spatial scales roughly between 10 and 1000 km. It is found that the inhomogeneous io nospheric conductivities affect the system dynamics substantially. Thi s feature is essential when the model is used to study the development of auroral forms.