Effects of the Grid Spacing and Background Wind on the Daily Air-Sea Coupling Over the Mediterranean Sea in HighResMIP

Abstract

This study delves into the nuanced dynamics of daily air-sea coupling across varying grid spacing over the Mediterranean Sea. Two fundamental thermal feedback mechanisms namely downward momentum mixing (DMM) and pressure adjustment (PA), are investigated using the High-Resolution Model Intercomparison Project (HighResMIP) model data at different oceanic and atmospheric resolution during 1990–2014. Most models show a stronger PA coupling and a weaker DMM coupling with respect to the satellite observations, which are found to increase with increased oceanic grid spacing, with considerable intermodel variability. The ECMWF MR shows the highest skill in simulating PA, while CMCC VHR shows the highest skill in simulating DMM. The investigation uncovers background wind speed-dependent variations in the air-sea coupling. DMM coupling is maximum for intermediate background wind speed, while PA coupling is minimum for intermediate background wind speed. Seasonality in the strength of the coupling is also detected and in the model data, it seems to be controlled by the large-scale wind speed, which is opposite to what is found in observations. This, together with the fact that simulations with identical atmospheric resolutions exhibit significant disparities in coupling strength, underscore a critical gap in the skills of global coupled models that goes beyond the use of high resolution and involves the critical role of model physics, such as convection and atmospheric boundary layer schemes.