3. The RO-ATMS and RO-AIRS inversion algorithms

#### 3.1 RO-ATM inversion algorithm

As mentioned above, MiRS is a MW inversion package used by NOAA to perform a physical-based microwave retrieval in all-weather scenarios over all landsurface types. The MiRS data products have been routinely assessed using independent measurements [9, 11, 12]. The MiRS package can be downloaded, for free, at http://mirs.nesdis.noaa.gov/download.php. In this study, we revised the current MiRS algorithm and use measurements from ATMS collocate with RO data to develop an enhanced RO-ATMS inversion algorithm (i.e., RO-MiRS). We included the RO refractivity forward operator (Eq. (1)) into the RO-MiRS algorithm.

#### 3.2 RO-AIRS inversion algorithm

Ref. [34] has detailed the information content for AIRS, RO, and the combined AIRS with RO for temperature and water vapor retrievals. Similar to the AIRS V6, the RO-AIRS inversion system is a 1D-var physical inversion system that retrieves the temperature and water vapor profiles sequentially. The updated fast and accurate AIRS transmittance model (Standard Alone AIRS-Radiance Transfer Algorithm package—SARTA [47]) is served as an AIRS forward operator. The configurations of background covariance matrix, error covariance matrix, and a priori used in the concurrent RO-AIRS retrieval are detailed in [48] and are not further descripted here.
