Observed Mesoscale Wind Response to Sea Surface Temperature Patterns: Modulation by Large-Scale Physical Conditions

Highlights: What are the main findings? Satellite observations confirm the control of large-scale wind speed and atmospheric stability on mesoscale SST-wind coupling. Observations reveal a more linear relationship between wind divergence and SST gradients and a more consistent dependence of the coupling on environmental conditions compared to reanalysis data, which show stronger nonlinearities and regional differences. What is the implication of the main finding? In addition to large-scale wind and atmospheric stability, boundary layer height and the spatial scale of the SST features play a major role in modulating the coupling intensity. Reanalysis data show important limitations in their representation of SST-wind coupling in stable conditions, likely due to an overestimation of boundary layer depth. Sea surface temperature (SST) gradients modulate surface wind variability at the mesoscale O(100 km), with relevant impacts on surface fluxes, rainfall, cloudiness and storms. The dependence of the SST-wind coupling mechanisms on physical environmental conditions has been proven using global ERA5 reanalysis data, regional observations and models. However, recent literature calls for the need of an observational confirmation to overcome the limitations of numerical simulations in representing such turbulent processes. Here, we employ O(10 km) MetOp A observations of surface wind and SST to verify the dependence of the downward momentum mixing (DMM) mechanism on large-scale wind U and atmospheric stability. We propose a simple empirical model describing how the coupling intensity varies as a function of U, where we account for the role of the characteristic SST length scale LSST and the boundary layer height h in determining the balance between the advective and response timescales, and therefore the decoupling of the atmospheric response from the SST forcing due to advection. Fitting such a model to the observations, we retrieve a scaling with U that depends on the atmospheric stability, in agreement with the literature. The physical interpretation from ERA5 is confirmed, albeit relevant discrepancies emerge in stable regimes and specific regional contexts. This suggests that global numerical models are not able to properly reproduce the coupling in certain conditions, which might have important implications for air–sea fluxes.