Initialization of Upper Ocean Temperature towards Forecast Improvements in GFSv17

Upper ocean temperature plays a critical role in the coupling of atmospheric and oceanic processes in numerical weather prediction (NWP). The sea surface temperature (SST) diurnal cycle, i.e., the variability of upper ocean temperature as determined by the daily cycle of solar radiation, is critical for accurately computing air-sea heat fluxes and predicting the system’s evolution. Inaccurate representations of the SST diurnal cycle in NWP initialization can lead to biased heat budget estimates, consequently degrading the skill of coupled forecasts. In this study, we present a conceptual demonstration of an updated SST observation operator designed to improve the initialization and coupled forecast of upper ocean temperature in the NOAA/NCEP Unified Forecast System (UFS)-based Global Forecast System version 17 (GFSv17).