WCD-23. Understanding the Observed Trade-wind Cloudiness Enhancement over Warm SST Anomalies using Large Eddy Simulations

Abstract
Feedbacks from ocean mesoscale sea surface temperature (SST) anomalies on atmospheric shallow convection are potentially important for climate projections. Advancing our understanding of these relatively small-scale processes was one main motivation for the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC). During the ATOMIC period, satellite composites show that trade-wind cloudiness and 10-m neutral wind speed are weakly enhanced (reduced) above the warm (cold) SST anomalies, with surface convergence anomalies located downwind around the maximum SST gradient. Motivated by these results, we investigate the associated mechanism linking SST and shallow cloud by conducting idealized large eddy simulation (LES) with the System for Atmospheric Modeling (SAM). SAM LES is initialized and forced with large-scale Eulerian conditions from ERA5. In the control experiment, the prescribed SST is spatially uniform; in the perturbation experiments, a Gaussian SST warm anomaly is placed at the center of the LES domain, with the domain mean SST preserved as that in the control case. The magnitude of the warm anomaly is varied from 0.25 K to 2 K. SAM simulated surface wind and cloudiness response to these SST perturbations will be discussed relative to the satellite composites.