Response of the atmospheric boundary layer to SST variability in a coupled simulation in the Atlantic trades

The coupling between the atmosphere and the ocean at the oceanic mesoscale (∼ 100–1000 km) plays a significant role in shaping the energy exchanges between the two fluids. We investigate how such coupling is represented in a state-of-the-art high resolution ocean-atmosphere coupled numerical simulation. In particular, we look into the thermodynamic adjustment of the marine atmospheric boundary layer (MABL) to sea surface temperature (SST) spatial anomalies. Mesoscale SST impacts the lower-tropospheric static stability by modifying the surface turbulent fluxes; these changes can be traced up to the top of MABL as a consequence of the modified air column buoyancy, with a subsequent impact on MABL top entrainment fluxes. Alongside, MABL temperature is found to partially adjust to SST, whereas MABL humidity does not, as surface evaporation and the entrainment of dry air mass at top-of-MABL have opposing effects which partially balance out: this results in a high sensitivity (∼ 25 % K−1) of the anomalous surface latent heat fluxes to mesoscale SST anomalies. Our findings, thus, indicate that small scale SST variability can have upscaling effects on the surface energy exchanges via non-linear MABL responses.