Current State of Satellite-Derived Wind Assimilation in NCEP GSI
Satellite-derived wind assimilation in NCEP’s GSI has undergone development and testing to accommodate upgrades to the global observing system’s fleet of geostationary and low-Earth orbiting satellites and changes to AMV and scatterometer wind algorithms. These development activities are an ongoing effort as prior-generation satellites are replaced, new satellites are added, and product algorithms are changed or introduced. These changes can have impacts on the global coverage of satellite-derived winds and on the subsequent NWP analysis and forecast.
Necessary changes have been made to NCEP GSI to replace Himawari-8 AMVs with AMVs from Himawari-9, and SEVERI AMVs from Meteosat-9 to replace those from Meteosat-8. AVHRR AMVs from Metop-B have undergone algorithm changes and Metop-C AVHRR AMVs have been added; a similar replacement of Metop-B winds and adoption of Metop-C winds has taken place for surface wind observations from ASCAT. AMVs from VIIRS have adopted GRR new cloud mask and cloud phase products; both VIIRS AMVs and AMVs from combined geostrophic and low-Earth orbiting (LeoGeo) are part of GFSv16.3.4. The impact of GOES-17 focal plane module overheating on AMVs has been mitigated by algorithm changes producing winds from separate channels during periods of peak heating. Looking to the future, tests are ongoing to evaluate GOES-18 AMVs as a replacement for GOES-17 and a change at NESDIS from use of the baseline algorithm to the Enterprise Algorithm for GOES AMV production.
A summary of winds assimilation testing for these changes will be provided, including comparison of observation coverage, observation fit to the model background, and impact of assimilating observations on forecast skill scores relative to both self-analysis and observation.
