Mesoscale Surface Wind-SST Coupling in a High-Resolution CESM Over the KE and ARC Regions

A strong positive correlation exists between mesoscale sea surface temperature (SST) and surface wind stress perturbations in the extratropical oceans, which is revealed by high-resolution satellite but is difficult to be accurately simulated in low-resolution coupled ocean-atmosphere models. The extent to which the mesoscale coupling is captured in a high-resolution Community Earth System Model (CESM-HR) is assessed in this study, with a focus on two regions, the Kuroshio Extensions (KE) and Agulhas Return Current (ARC), respectively. Compared with satellite observations, it is found that the CESM-HR can well depict the characteristics of the mesoscale air-sea coupling, with its strength being comparable to that observed; but in the KE region, the simulated strength is only half of the observed during summer. Mechanisms for the atmospheric responses to mesoscale SST perturbations through the pressure adjustment (PA) and the downward momentum transport (DMT) are analyzed. The results highlight different mechanisms for controlling the atmospheric responses over the KE and ARC regions, which are regionally and seasonally dependent. In the ARC region, pronounced dipole patterns of sea surface pressure (SLP) and vertical velocity perturbation responses indicate that the DMT exerts a dominant effect in both winter and summer. In the KE region, monopole patterns show the main role played by the PA mechanism for the atmospheric adjustment in summer, while dipole patterns indicate the main role played by the DMT mechanism in winter. The weak coupling strength in summer over the KE is closely related to the inadequate parameterization of vertical heat mixing.

Automated summary

The study reveals that the high-resolution CESM-HR model can accurately capture the characteristics of mesoscale air-sea coupling, but there are still discrepancies in some regions and seasons compared to actual observations. Additionally, the atmospheric responses to mesoscale SST perturbations vary depending on the region and season.