Ionosphere/Thermosphere Studies Using the GAIM-Physics-Based Data Assimilation Models (Invited)

Studies of the ionosphere/thermosphere system at low and mid latitudes are often limited by our current understanding and specification of solar variability, the coupling processes in the ionosphere-thermosphere system and the coupling between the high and low latitude regions. Furthermore only a limited number of observations are available for a specification of ionosphere/thermosphere dynamics and weather at these latitudes. As shown by meteorologists and oceanographers, the best specification and weather models are physics-based data assimilation models that combine the observational data with our understanding of the physics of the environment. Therefore, we have developed and continue to develop four data assimilation models; two for the ionosphere, one for the high-latitude ionosphere dynamics, and one for the thermosphere. One of these models is the Global Assimilation of Ionospheric Measurements Full-Physics model (GAIM-FP). The model is based on an Ensemble Kalman filter technique and a physics-based model of the ionosphere/plasmasphere (IPM), which covers the altitude range from 90 to 20,000 km, includes six ion species, is based on the International Geomagnetic Reference Field (IGRF), and allows for inter-hemisphere flow. The model can assimilate bottom-side N_e profiles from ionosondes, slant TEC from ground-based GPS stations, in situ N_e from the DMSP satellites, occultation data from several satellites, and line-of-sight UV emissions measured by satellites. As an output the assimilation model provides the 3-dimensional density distribution throughout the ionosphere and information about the physical drivers, including the neutral winds, composition and electric fields. For the current study, a multitude of ground- and space-based ionospheric observations were assimilated to specify the 3-dimensional global morphology of the low- and mid-latitude ionosphere/thermosphere and the various driving forces. Examples of the ionosphere morphology obtained from our model runs will be presented with an emphasis on the relationship between the electron density distribution and the neutral wind, neutral composition, and electric field forcing.