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

Abstract

The understanding of the upper atmosphere coupling mechanisms 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 a period of quiet solar geomagnetic conditions (4-8 March 2008) using the physics-based Coupled Thermosphere Ionosphere Plasmasphere electrodynamics model (CTIPe) coupled to an ensemble Kalman filter (EnKF) assimilation scheme, the Thermosphere-Ionosphere Data Assimilation (TIDA). 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.