Ionospheric Dynamics at Low Latitudes Obtained From the USU Physics-Based Data Assimilation Model (GAIM-FP)

The ionosphere-thermosphere system at equatorial and low latitudes is strongly coupled, and therefore, a study of ionospheric dynamics must take into account the interaction between the different domains. Over the past decades meteorologists and oceanographers have used data assimilation models to study complex systems. We have developed two data assimilation models with different complexity and both provide global and regional specifications of the 3-dimensional ionosphere-plasmasphere plasma densities. One of these models is a Full Physics-Based Kalman filter data assimilation model (GAIM-FP), which is based on a physics- based model for the ionosphere-plasmasphere system, a diverse array of data sources, and an ensemble Kalman filter data assimilation technique. This model covers the ionosphere-plasmasphere system from 90 to 30,000 km altitude and includes 6 ion species (NO+, N2+, O2+, O+, He+, H+). An important strength of this model is that in addition to the global and regional 3-D ionosphere electron density distribution it also determines the corresponding ionospheric drivers, including the thermospheric neutral winds and the low-latitude electric fields. The model can assimilate a variety of different data types, including GPS/TEC from hundreds of ground receivers, in situ Ne from several DMSP satellites, bottomside Ne profiles from tens of ionosondes, and occultation data from the six COSMIC satellites. With the recent launch of the C/NOFS satellite the possibility has opened to also assimilate data from the various instruments onboard this satellite. In the present study, we have used the model to study the dynamics of the equatorial and low latitude ionosphere over the American sector, where ground-based ionospheric observations are abundant. The model was used to determine the various driving forces and to study their temporal and spatial variability. We will present examples of the ionospheric and driver specifications obtained from our model runs and the results will be compared with independent data. If C/NOFS observations will become available before the presentation of this paper initial comparisons of our model results with C/NOFS observations will also be shown.