Unveiling the Influence of the Daily Oceanic (Sub)Mesoscale Thermal Feedback to the Atmosphere

Abstract Oceanic mesoscale ( O (100 km)) Thermal Feedback (TFB) can modify the marine atmospheric boundary layer through two main mechanisms: Downward Momentum Mixing (DMM) and Pressure Adjustment (PA). In this study, we use ERA5 reanalysis, with the finest spatial resolution available (roughly 25 km globally), and a set of coupled ocean-atmosphere model experiments to investigate the extent to which the spatial resolution of oceanic fine scale structures ( O (10)-100 km) influences the TFB mechanisms on a daily timescale in the northwestern tropical Atlantic. We show that the low-level wind magnitude response to sea surface temperature anomalies is controlled by large oceanic mesoscale structures (>100 km), whereas finer structures play a minor role. However, the TFB mechanisms vary considerably depending on whether the mesoscale structures are fully represented or not. The DMM and PA mechanisms are diminished by about 36% and 85%, respectively, when the full range of mesoscale structures in the ocean is resolved. This reduction is associated with both a stronger atmospheric frontogenesis mechanism induced by submesoscale ( O (10 km)) oceanic thermal structures and the divergence of submesoscale ocean currents, which is not the case at the large mesoscale. These processes have the potential to exert a destructive influence on the daily oceanic mesoscale TFB by inducing opposite low-level atmospheric vertical velocities, which is particularly enhanced in the case of the PA mechanism. Finally, our findings suggest that climate models must accurately represent fine scale ocean thermal structures that directly influence TFB mechanisms and potentially affect cloud formation and precipitation patterns.