Highlights of theoretical progress related to the International Magnetospheric Study

The goals of the International Magnetospheric Study (IMS) have been addressed by a variety of U.S. theoretical research efforts within three broad areas: (1) the solar wind/magnetosphere interaction, (2) the substorm dynamics of the magnetospheric tail, and (3) the electrodynamic magnetosphere/ionosphere interaction. In area 1, an important development is the suggestion that magnetic merging may occur predominantly near the polar cusps rather than near the subsolar point; this hypothesis has several interesting consequences, including the possibility that a large area of the dayside magnetopause may be magnetically closed even in the presence of a significant level of magnetic merging at the cusps. Several potential mechanisms have been identified to account for noncollisional diffusion of solar wind plasma across such a closed magnetopause. In area 2, the importance to magnetotail dynamics of a continuous source of solar wind plasma and of sporadic plasma loss associated with an unsteady convection cycle has been stressed, although self‐consistent models incorporating these effects have yet to be developed. In area 3, basic understanding of the relevant physics appears to be relatively advanced, both with respect to magnetosphere/ionosphere coupling in the subauroral region and with respect to the large‐scale structure of auroral zone electric fields parallel and perpendicular to the magnetic field. Significant progress has been made in quantitative global modeling of the magnetosphere/ionosphere interaction in sufficiently realistic detail to interact directly and productively with the IMS observational program.