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IOVWST Meeting
Portland, Maine, USA, 2019

On the Sensitivity of Numerical Simulated Mesoscale Air-sea Coupling

Presenting Author: Dr. Qingtao Song

It is well established from satellite observations of near-surface winds and SST from QuikSCAT and the Advanced Microwave Scanning Radiometer, as well as from numerical model simulations, that near-surface winds in the atmosphere are modified in the vicinity of oceanic fronts throughout the World Ocean. However, the response of the wind stress produced from operational Numerical Weather Prediction (NWP) models is only about half as large as is observed in the satellite data. This study presents an analysis of the sensitivity of simulated air-sea coupling between mesoscale surface winds and small-scale SST variability to the resolution of the SST boundary condition, grid resolution, horizontal diffusion, and vertical mixing. A series of simulations were made with the Weather Research and Forecasting (WRF) model for the Agulhas Return Current (ARC) region in the South Indian Ocean. We show that the resolution and accuracy of the SST boundary forcing and the accuracy of model parameterizations of vertical mixing in the marine atmospheric boundary layer (MABL) are the leading order factors in determining the accuracy of model simulations of this coupling. It is found that the weak coupling of surface wind speeds from the ECMWF model to SST is likely attributable primarily to the weak response of vertical turbulent mixing to SST-induced stability in the parameterization of boundary layer turbulence. Further sensitivity studies with the WRF model found that the entire atmosphere adjusts to the forcing associated with the SST front, with the largest changes in wind speed near the bottom of the MABL and vertical propagation of wave motions induced by the SST front.

2019 International OVWST Meeting
May 29-31 in Portland, Maine, USA
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