Towards Atmosphere-Ocean Coupled Assmilation with the GEOS: Skin SST developments & analysis of MW observations

Usage of bulk retrieved SST as a boundary condition for the Atmospheric Data Assimilation System (ADAS) is not an accurate representation of the skin SST, because it does not resolve near sea-surface stratification in temperature brought about by diurnal warming, wind stress and surface currents.

En route to the development of an Integrated Earth System Analysis (IESA), the NASA-GMAO ADAS has been extended to model and analyze skin SST using an air-sea interface layer. This layer modifies the near-surface ocean temperature (or bulk SST) to include near-surface effects, such as diurnal warming due to solar insolation, cool-skin, change in surface stress due to waves, that were previously not felt by the lower atmosphere. GSI based direct assimilation of IR and MW radiance observations that includes SST sensitive channels allows us to obtain a realistic, diurnally varying skin SST. The relevant IR observations are within 10-12 microns (for e.g., AVHRR) and 10GHz (TMI-TRMM, GMI-GPM).

Using the statistics of Observation-Minus-Background and Analysis, we quantify the impact of IR and MW data on the skin SST. We focus on the challenges of assimilating 10 GHz frequency channels using the CRTM, FASTEM-5 infrastructure that is relevant to the JCSDA. Using evaluation metrics such as air-sea fluxes, coupling between SST and surface wind speed, we validate our results.