Implementation of a Coupled Atmosphere-Wave-Ocean Model in the Mediterranean Sea: Sensitivity of the Short Time Scale Evolution to the Air-Sea Coupling Mechanisms
Abstract:In this study a coupled regional atmosphere-wave-ocean model has been implemented in the Mediterranean Sea and applied to the simulation of the atmospheric circulation and of the upper ocean structure on the short time scale range typical of regional meteorological predictions. The coupling accounts for the feedback of the upper ocean on the atmospheric circulation, that is for the variation of the SST (Sea Surface Temperature) during the development of the cyclones and for the dependence of the SSR (Sea Surface Roughness) on the wind-wave spectrum. The model can operate also in uncoupled mode, with prescribed SST and SSR computed using the Charnock formula (depending on wind speed only). Six case-studies, characterized by strong cyclones and intense air-sea interaction, have been analyzed. A sensitivity analysis is carried out by comparing uncoupled and coupled simulations, carried out including the SST and SSR-feedbacks both separately and simultaneously. The feedbacks have systematic effects on the atmospheric precipitation, on heat and momentum fluxes, and, consequently, on MLD (Mixed Layer Depth), SST, and SWH (Significant Wave Height). For all these quantities, except for SWH, the two feedbacks act in opposite directions. The effect of the SST feedback is larger on latent heat flux, precipitation, sea surface cooling, and, marginally, on mixed layer growth and it determines their reduction when the two feedbacks act simultaneously. The SSR and SST-feedbacks have comparable effect on the SWH field and they both contribute to the SWH reduction. Though the SLP (Sea Level Pressure) and Geopotential minima of single "fall" case-studies can be appreciably modified by the inclusion of the feedbacks, no systematic effect has been identified in these fields, presumably because of the intrinsic unpredictability of the atmospheric circulation.
Document Type: Research Article
Publication date: March 1, 2003