Hindcasting the ionosphere via assimilation of neutral mass density into physics-based models.

Understanding the coupling mechanisms that occur in the upper atmosphere depends to a large extent on an accurate estimate of the true state of the Thermosphere - Ionosphere system. We assimilate measurements into physics-based models to provide a better estimate of the state of the system than the one obtained using the model alone. Some of the most important parameters that define the state of the thermosphere are neutral composition and density. Since their changes can modify the production-loss processes and impact the plasma density, in this study we assimilate neutral mass density measurements to evaluate the impact that changes in the thermosphere produce in the ionosphere.

The analysis is done during quiet solar geomagnetic conditions using the physics-based Coupled Thermosphere Ionosphere Plasmasphere electrodynamics model (CTIPe) and the Thermosphere Ionosphere Electrodynamics General Circulation model (TIE-GCM). They are coupled to two different ensemble Kalman filter assimilation schemes, the Thermosphere-Ionosphere Data Assimilation (TIDA) scheme and the Data Assimilation Research Testbed (DART) respectively. The model results from assimilating accelerometer-derived neutral mass density from CHAMP and GRACE are compared with neutral mass density independent measurements to assess the changes in the thermosphere. Total Electron Content (TEC) observations from the International GNSS Service (IGS) as well as ionosonde data from the GIRO database are used to evaluate the effect over the ionosphere.

Preliminary results show an improvement of the model thermosphere through assimilation, as well as, significant differences in TEC between the background model run and model with assimilation scheme. These differences could be an indicator of how the ionosphere is affected by the assimilation of thermospheric observations.