A Case Study of Impact of Sea Surface Temperature Variability on Boundary Layer Wind Structure

The observations of the recent field experiment, Coupled Boundary Layer/Air-Sea Transfer, showed significant sea surface temperature (SST) variability in the northeastern coastal area of the United States. On 18 August 2003, aircraft measurements revealed a cold SST anomaly with 6 K difference over 13 km. Associated with the SST variability, both air temperature and wind speed measurements exhibit significant variability. The turbulence measurements also showed corresponding variations. To understand the impact of the SST variability, we used U.S. Naval Research Laboratory's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) to simulate this case. We first performed SST analysis, which includes all available in situ SST measurements in combine with satellite data, producing SST field every 6 hours. We then used this SST field as lower boundary conditions for high resolution (27, 9, 3, 1 km) COAMPS at-mospheric simulations. We have found from our simulations that the SST cold anomaly has sig-nificantly changed boundary layer structure due to its impacts on the pressure and boundary layer stability. Particularly, the wind speed is decreased as the pressure is redistributed and downward momentum flux is reduced. Furthermore, the boundary-layer response time scale to the SST cold anomaly depends on the background winds and surface layer characteristics such as the stability and roughness lengths.