EMPIRICAL-MODELS OF THE MAGNETOSPHERIC MAGNETIC-FIELD

Space scientists have a wide variety of models to choose from for thei r studies of the Earth's auroral phenomenon, radiation belts, magnetot ail, magnetopause, etc. Different types of models are suited for diffe rent purposes. At this time, there is no one model to suit everyone's needs. In this paper a general overview of magnetospheric modeling is given, along with a more detailed discussion of several empirical mode ls which are widely used. These models are composed of representations of the Earth's main internal field (basically a dipolar field), plus external field contributions due to ring currents (carried by the part icles in the Van Allen radiation belts), magnetopause currents (the bo undary surface between the Earth's magnetic field and the interplaneta ry magnetic field carried by the solar wind), and tail currents (carri ed by particles in the neutral sheet of the magnetotail). As in many d isciplines, models are frequently chosen for convenience rather than f or their intrinsic properties. Here a summary of the properties of the most commonly used models is given. Discussion of MHD models is beyon d the scope of this paper. The empirical models presented here are the Mead-Fairfield, Olson-Pfitzer tilt-dependent (1977 Tsyganenko-Usmanov , Tsyganenko (1987), Olson-Pfitzer dynamic (1988), Tsyganenko (1989), and Hilmer-Voigt models. The derivations, agreement with quiet time an d storm time data from the two satellite programs SCATHA and CRRES, an d computation requirements of these models are compared.