Evaluation and Improvement of the S-NPP CrIMSS Rain Flag

As part of the Suomi National Polar-orbiting Partnership (S-NPP), Crosstrack Infrared and Micrwoave Sounding Suite (CrIMSS), a joint system that utilizes the Crosstrack Infrared Sounder (CrIS) and the Advanced Technology Microwave Sounder (ATMS) in synergy, an ATMS only rain flag is utilized to edit out potentially rain contaminated scenes that will lead to degraded temperature and moisture profiles.

The original, pre-launch rain flag has been shown to incorrectly map areas of rainfall, with very little rain evident in the Intra-tropical Convergence Zone (ITCZ) and over land areas, and too much rain over mid-latitude ocean regions. This can be attributed to the use of an outdated AMSU-A only rain algorithm, which additionally was not implemented properly.

To improve the CriMSS rain flag algorithm, a more accurate scheme built off the NOAA/NESDIS Operational Microwave Surface and Precipitation Products System (MSPPS) precipitation algorithm heritage was developed. In particular, ATMS channels were matched as closely as possible to their AMSU/MHS counterparts; some empirical adjustments were made to account for some frequency and primary polarization differences between the sensors. Comparisons against independent rain products from other satellites and ground observations show that the new rain flag is more realistic and it is expected to improve the evaluation of the corresponding CrIMSS temperature and moisture profiles over non-precipitation conditions. It will be incorporated into the CrIMSS MX7.1 operational version.

Other aspects of the algorithm, including its performance at various spatial resolutions (i.e., native ATMS vs. footprint averaged to match the CrIS) and use of a climatological wind speed over the ocean will also be presented.