An integral component of the multi-agency U.S. Global Change Research Program (Our Changing Planet," Committee on Earth Sciences, 1991) is understanding and modeling the geospace environment. As part of its contribution to the U.S. Global Change Research Program, the National Science Foundation's Division of Atmospheric Sciences has established a new research initiative, Geospace Environment Modeling (GEM), with the goal of supporting basic research into the dynamical and structural properties of geospace, leading to the construction of a global geospace model with predictive capability. The subjects of the first GEM campaign are the magnetospheric boundary, the magnetosheath beyond it, and the connection from the boundary through the magnetosphere to the ionosphere. This grant is to use low-altitude spacecraft data to test and refine the open-magnetosphere model of Toffoletto and Hill ?1989! with respect to the mapping of the cusp to low altitude. The model provides quantitative predictions of the local time extent and locations of the equatorward boundary of the cusp as a function of the cross-polar-cap potential.
