A high-resolution, three-dimensional, time dependent, nested grid model of the coupled thermosphere-ionosphere

First results are presented from a 3-D, time dependent, high resolution, nested grid model that has been developed to study mesoscale processes in the global, coupled thermosphere-ionosphere system. This new Thermosphere-Ionosphere Nested Grid (TING) model, which is an extension of the National Center for Atmospheric Research's thermosphere-ionosphere general circulation model (NCAR-TIGCM), runs on a UNIX workstation. The TING model simultaneously calculates global (coarse resolution) and local (high resolution) distributions of neutral and plasma winds, temperature and composition. It is comprised of two coupled codes - a global TIGCM and an adjustable nested grid code which uses the same solvers as the TIGCM, but has higher spatial and temporal resolution. The size, location and level of nesting of the high resolution grid(s) are adjustable to suit the specific application. The coupling between the coarse (TIGCM) grid and the nested interior grids is via a 'one-way interaction' scheme. In this scheme, the TIGCM output influences the nested grid model by providing initial conditions and temporally evolving boundary conditions, but the outputs from the nested grid are not permitted to influence the TIGCM. Diurnally-reproducible results of the TING model are presented for solar-maximum, winter solstice, geomagnetically-quiet conditions. The TING model successfully simulates well-known thermosphere-ionosphere features that are smeared or not modeled at the spatial resolutions used in standard TIGCM's. These include the sub-auroral electron density trough, the polar cap 'hole' and the polar cap 'tongue of ionization'.