Observational evidence of the preferential occurrence of wind convergence over sea surface temperature fronts in the Mediterranean

Air and sea interact on a wide range of scales, shaping climate and influencing weather. The direct effect of sea surface temperature (SST) structures on the extratropical atmosphere at the daily time-scale is generally masked by the large variability associated with atmospheric dynamics. With 25 years of daily SST and surface wind observational products, obtained with data from buoys, satellite and atmospheric analysis in the Mediterranean, we show that strong surface wind convergence preferentially occurs when the air encounters a cold SST front. The mechanism responsible for the influence of ocean fronts on surface winds is rooted in the thermal disequilibrium that emerges at the air–sea interface, where cold water enhances the stability of the boundary layer, decoupling surface winds from the stronger winds aloft. Surface convergence drives upward motion which, under appropriate conditions, favours cloud formation. Thus, these results suggest that weather forecast models need to properly represent the small-scale ocean thermal structures, which could affect rainfall.