Effects of Swarm neutral mass density assimilation in the ionospheric state estimate during St. Patrick’s Day storm 2015

Abstract

During geomagnetic storms, rapid changes in the upper atmosphere can dramatically affect communication and navigation instruments. Therefore, it is necessary to monitor these events through a good representation of the thermosphere-ionosphere (TI) system. This can be achieved by assimilating data into physical models by means of an ensemble Kalman filter. Due to the coupled nature of the TI system, the ionosphere can be affected by, among others, changes in the neutral atmosphere, especially during storm conditions. In this study, we investigate the ability of the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics physics-based model (CTIPe) to improve the representation of the ionosphere by assimilating Swarm neutral mass density during the 2015 St. Patrick's Day storm. To gauge the ionospheric improvement due to data assimilation we compare the results of the assimilation and non-assimilation runs with along the orbit electron density measurements of GRACE satellite. The results show a reduction in the root mean square error (RMSE) by a 22% with respect to the non-assimilation run. The impact on the global scale is evaluated by comparing CTIPe results with the corresponding output of the 3D B-Spline electron density model. The electron density results show that the equatorial region is the most affected area by the assimilation of neutral density.