An Analysis of Alternatives for the COSMIC-2 Constellation in the Context of Global Observing System Simulation Experiments
Observing System Simulation Experiments (OSSEs) were conducted to evaluate the potential impact of the six Global Navigation Satellite System (GNSS) radio occultation (RO) receiver satellites in equatorial orbit from the initially proposed Constellation Observing Satellites for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) mission, known as COSMIC-2A. Furthermore, the added value of the high-inclination component of the proposed mission was investigated by considering a few alternatives architecture designs, including the originally proposed polar constellation of six satellites (COSMIC-2B), a constellation with a reduced number of RO receiving satellites, and a constellation of six satellites but with fewer observations in the lower troposphere. The 2015-year version of the operational three-dimensional ensemble-variational data assimilation system of the National Centers for Environment Prediction (NCEP)’s was used to run the OSSEs. Observations were simulated and assimilated using the same methodology and their errors assumed uncorrelated.
The largest benefit from the assimilation of COSMIC-2A, with denser equatorial coverage, was to improve tropical winds, and its impact was found overall neutral in the extratropics. When soundings from the high-inclination orbit were assimilated in addition to COSMIC-2A, positive benefits were found globally, confirming that a high-inclination orbit constellation of RO receiving satellites is necessary to improve weather forecast skill globally. The largest impact from reducing COSMIC-2B from six to four satellites was to slightly degrade weather forecast skill in the northern hemisphere extratropics. The impact of degrading COSMIC-2B to COSMIC level of accuracy, in terms of penetration into the lower troposphere, was mostly neutral.