A regional coupled model for studies of mesoscale air-sea interaction in the Southern Ocean

This study presents a regional high-resolution atmosphere-ocean coupled model with a realistic atmospheric component and a semi-idealized oceanic model of a zonal flow, designed for studies of the atmosphere-ocean interactions at the scales from 10 to several hundreds of kilometers. The atmospheric model consisted of two nested domains: the inner domain fully coupled with the ocean model, and the outer domain one-way coupled with the observed SST. Two 2-year simulations are discussed here: one in which the oceanic isopycnals are steep and ocean currents are strong (“Strong Currents” or SC) and another – with less steep isopycnals and weaker currents (“Weak Currents” or WC). Simulated mesoscale variability occurs on a wide range of spatial scales, and we distinguish large-mesoscale (hundreds of kilometers and shorter) and small-mesoscale (tens of kilometers and shorter) anomalies in these studies.

Relationships between atmospheric variables and SST are studied using temporal correlations and coupling coefficients, and for both large-mesoscale and small-mesoscale anomalies. Consistent with the Vertical Mixing Mechanism (VMM), which implies an acceleration of winds over warm SST anomalies, we find significant positive correlations between large-mesoscale anomalies in the following pairs of variables: equivalent neutral stability (ENS) 10-meter winds and SST, wind stress and SST, and wind stress divergence/curl and SST along-wind/cross-wind gradients. The temporal correlations were smaller for the small-mesoscale anomalies. The correlation coefficients were also higher for the SC region, but the corresponding coupling coefficients were higher for the WC region. Among all pairs, the coupling coefficients for the ENS winds and SST were found to be most robust. Coupling coefficients for the wind stress also vary in time and show a nearly linear dependence on the ENS wind speed, whereas the coupling coefficients for the ENS wind and SST have a less obvious response to the ENS winds. The reported variability in these coupling coefficients indicates a complex, nonlinear relationship between the wind and SST anomalies. The relative importance of the Pressure Adjustment Mechanism was studied in both the WC and SC domains, using a correlation between the surface pressure Laplacian and ENS wind convergence.