Recent Impact of COSMIC-2 with Improved Radio Occultation Data Assimilation Algorithms

A Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) follow-on constellation, COSMIC-2, was successfully launched into equatorial orbit on 24 June 2019. With an increased signal-to-noise ratio due to improved receivers and digital beam-steering antennas, COSMIC-2 is producing about 5000 high-quality radio occultation (RO) profiles daily over the tropics and subtropics. The initial evaluation of the impact of assimilating COSMIC-2 into NOAA's Global Forecast System (GFS) showed mixed results, and adjustments to quality control procedures and observation error characteristics had to be made prior to the assimilation of this dataset in the operational configuration in May 2020. Additional changes in the GFS that followed this initial operational implementation resulted in a larger percentage of rejection (;90%) of all RO observations, including COSMIC-2, in the mid-to lower troposphere. Since then, two software upgrades directly related to the assimilation of RO bending angle observations were developed. These improvements were aimed at optimizing the utilization of COSMIC-2 and other RO observations to improve global weather analyses and forecasts. The first upgrade was implemented operationally in September 2021 and the second one in November 2022. This study describes both RO software upgrades and evaluates the impact of COSMIC-2 with this most recently improved configuration. Specifically, we show that the assimilation of COSMIC-2 observations has a significant impact in improving temperature and winds in the tropics, though benefits also extend to the extratropical latitudes.