Evaluating Radio Occultation Constellation Designs using Observing System Simulation Experiments: Data Impact of Electron Density Profiles on Ionospheric Specification

Low Earth orbit (LEO) radio occultation (RO) constellations can provide global electron density profiles (EDPs) to better specify and forecast the ionosphere-thermosphere (I-T) system. This study uses Observing System Simulation Experiments (OSSEs) to assess the impact on ionospheric specification. EDPs retrieved from 10 sets of hypothetical RO constellation configurations are assimilated into a coupled I-T model. RO constellations here use the GPS and GLONASS systems, each containing 6 or 12 LEO satellite constellations designed with orbit parameter combinations of 520 km or 800 km altitude, and 24 degrees or 72 degrees inclination. These RO constellations are made to resemble the COSMIC constellations. The OSSEs are performed using the Ensemble Adjustment Kalman Filter (EAKF) implemented in the Data Assimilation Research Testbed (DART) and the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). The period of interest is the St. Patrick’s Day storm on March 13-18, 2015, including quiet and storm-time conditions. The Whole Atmosphere Model-Ionosphere Plasmasphere Electrodynamics (WAM-IPE) is used for the nature run that serves as the true ionosphere and from which synthetic EDP observations are derived. The plasma states simulated by TIEGCM thus are biased from WAM-IPE. This study assesses the performance of the different RO constellation designs in terms of the quality of the DART-TIEGCM OSSEs against the WAM-IPE truth. Performance is assessed using NmF2, hmF2, and global and regional root mean square error (RMSE) for high-, mid- and low-latitudes. The study furthermore shows how Abel inversion errors and model errors contribute to less-than-optimal OSSE performance.