GEOS S2S Version 3: The New GMAO High-Resolution Seasonal Prediction System (Invited Presentation)

The NASA/Goddard Global Modeling and Assimilation Office (GMAO) released Version 2 of the Subseasonal to Seasonal (GEOS-S2S) forecast system in the fall of 2017, and it has been producing near-real time subseasonal to seasonal forecasts and a weakly coupled atmosphere-ocean data assimilation record since then. A new version of the coupled modeling and analysis system (Version 3) was released by the GMAO at the end of 2019. The new version runs at higher oceanic resolution than the previous (approximately 1/2 degree for the atmosphere, 1/4 degree for the ocean), and includes interactive earth system model components not typically present in seasonal prediction systems (two moment cloud microphysics for aerosol indirect effect and an interactive aerosol model). The weakly coupled atmosphere-ocean data assimilation system now includes assimilation of sea surface salinity, that has been shown to result in improved ocean mixed layer simulation and ENSO prediction skill.

Here will describe the new system, which includes a novel strategy for ensembles, and present results from the test suite of retrospective seasonal forecasts. Results show improvements in ENSO prediction skill, and a much improved prediction of sea ice extent in both hemispheres. The surface air temperature over land and precipitation forecast skill are comparable to GEOS-S2S Version 2, and the only tradeoff is a weakened amplitude of the tropical annual cycle of the SST.