GEM: Global MHD Simulations of Dayside Magnetospheric Processes and Their Mapping to the Ionosphere

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9301051 Lyon Global MHD simulations of the interaction of the solar wind with the magnetosphere and ionosphere will be performed as an aid to interpreting and analyzing low altitude and ground-based observations done in conjunction with the GEM program. The calculations will use solar wind data for the actual period of the GEM observing campaigns to produce as accurate a representation of mangetospheric conditions as possible for those times. The results from the simulations will be mapped from the mangetopause and cusp regions to near earth space and to the ionosphere where they may be compared with observations. The primary quanities to be mapped will be magnetic field topology, field-aligned currents and particle distributions. Experience and theoretical considerations show that these mappings can provide useful information on the scales seen in the ground-based radar observations, for example, even though the calculation grid is relatively more coarse. The magnetic field model used for this mapping is determined self- consistently from the MHD solution for the magnetosphere. This model will also be used to map the ionospheric observations back out to the region of the magnetopause, and the field models will be provided to GEM participants. These comparison will lead to a better appreciation for the strengths and weaknesses of the global MHD model and what additional physics must be included. Studies will also be conducted with varying solar wind input data to cover a wide range of possible conditions. These simulations will then be used to provide a parametric representation of the normal field and the tangential velocity at the magnetopause. This representation is an important input to a modular magnetospheric circulation model. The time varying solar wind cases used for the observational campaigns will also be analyzed in this fashion to find how much of the actual magnetopause tangential eletric field can be prescribed by a static model. ***