## 1 Introduction
STAR has developed the stand-alone RO inversion package for converting COSMIC-2 Level 1a (phase delay) to Level 1b (excess phase) processing [32] and for converting Level 1b to Level 2 (bending angle and refractivity profiles) processing [33]. The STAR processed data can be used to understand the RO excess phase data quality and quantify the derived bending angle profiles' structural uncertainty when other RO processing centers implement different inversion methods and initialization approaches [29; 30; 31]. We also compared the STAR results with those produced by other RO centers (i.e., UCAR, Radio Occultation Meteorology Satellite Application Facility (ROM SAF), etc. [29; 30; 31]). We also use all available STAR RO data products to generate the monthly mean climatologies (MMCs) for climate studies. 2. The integrated calibration and validation (Cal/Val) system (ICVS) for data monitoring and climate comparisons. To routinely monitor the quality of multiple RO missions and identify the sudden quality change in the time series of RO data products, we developed the GNSS RO ICVS, see [[https://ncc.nesdis.noaa.gov/GNSSRO/ICVS/index.php](https://ncc.nesdis.noaa.gov/GNSSRO/ICVS/index.php)]([https://ncc.nesdis.noaa.gov/GNSSRO/ICVS/index.php](https://ncc.nesdis.noaa.gov/GNSSRO/ICVS/index.php)) (accessed on 26 September 2022). Using the system, we also compare climate data generated from multiple RO missions and reanalysis. 3. Multi-sensor calibration and validation system. The main goal of the STAR multi-sensor validation system is to evaluate data from various RO missions relative to IR/MW observations collected from multiple satellite missions through direct comparison or through converting RO data to IR/MW brightness temperatures (BTs) using radiative-transfer models (see Section 5). STAR is also a national satellite center where experts in satellite instruments for IR and MW sounders and in situ measurements (radiosonde) are under one roof. All MW and IR sounders from multiple satellite missions, including the NOAA-15, 18, 19, Suomi National Polar-orbiting Partnership (SNPP), NOAA-20 (N20), and the meteorological operational satellite (Metop) -A, -B, and -C are monitored by STAR's ICVS (see [[https://www.star.nesdis.noaa.gov/icvs/](https://www.star.nesdis.noaa.gov/icvs/)]([https://www.star.nesdis.noaa.gov/icvs/](https://www.star.nesdis.noaa.gov/icvs/)) (accessed on 26 September 2022)). 4. Demonstration of the RO impacts on NWP through data assimilation. We also assimilated COSMIC-2 data into NOAA's hurricane weather research and forecasting (HWRF) model through cycled forecasting experiments [34]. We are also interacting with NOAA's environmental modeling center (EMC) to provide the best error characteristics for RO data to improve the quality control criteria in NOAA's NWP system. Although we have documented the STAR RO L1a-L1b processing [32] and L1b-L2 processing [33] and demonstrated the COSMIC-2 data quality assessment [15; 35; 36; 37; 38; 39], we have not reported the STAR implementation to convert refractivity profiles to temperature and water vapor profiles. Retrieving atmospheric variables from the RO refractivity profile is an under-determined problem. Usually, using the one-dimensional variational (1D-Var) retrieval approach [5; 6] and combining the observations and a priori information can derive the temperature and water vapor profiles; however, since retrieving atmospheric quantities (temperature and water vapor) from a single RO measurement (i.e., refractivity) at the same pressure level is an ill-posed problem. Finding an optimal solution from RO refractivity is still challenging, especially in the low and moisture troposphere. This study aims to describe the STAR COSMIC-2 neutral atmospheric temperature and moisture profile inversion algorithms and validate their accuracy and uncertainty. We first describe the STAR inversion approaches to convert COSMIC-2 refractivity into temperature and water vapor profiles.