The spatial structure of the Mediterranean Sea winds revealed by ERS-1 scatterometer

Almost 5 years ( 1992-1996) of ERS-1 scatterometer wind data have been analysed over the Mediterranean Sea to study the spatial structure of the main regional wind systems. Examples of relevant winds (etesian, bora, mistral and libeccio) are discussed in the paper. The spatial structure of the winds has been studied through the Ekman pumping field, derived from the curl of the wind stress field. This has been computed by a boundary layer model, using scatterometer wind data, sea surface temperature ( SST) from the ERS-1 ATSR and the NOAA AVHRR radiometers and air temperature, humidity and atmospheric pressure from the European Centre for Medium Range Weather Forecasts ( ECMWF) analysis data. Since the Mediterranean Sea is surrounded almost entirely by mountains, several features of the wind fields appear induced by the orography. The most relevant examples concern the Adriatic Sea bora, which is spatially modulated close to the gaps of the Balkans chain, and the funnel effect occurring in the Tyrrhenian Sea, east of the Strait of Bonifacio, under south-westerly winds, producing a dipole-like structure of the atmospheric Ekman pumping. In the Gulf of Lion the orography affects the zonal extension of the mistral, while the Isle of Crete influences the flow of the etesian. Examples of the relationship between the air-sea fluxes ( heat and momentum) and the ocean dynamics revealed by SST fields are proposed analysing the characteristics of the mid-Levantine Basin in summer and of the north-western Mediterranean in winter, the areas best covered by scatterometer. In the mid-Levantine Basin there is a strong correlation between the summer mean atmospheric Ekman pumping and the mean SST structure. In the north-western Mediterranean Sea, the winter cyclonic circulation in the Gulf of Lion has been found associated with atmospheric suctions produced by the mistral. The gyre-scale circulation in the northern Tyrrhenian Sea, east of Bonifacio Strait, has also been found to be correlated with the spatial structure of the atmospheric Ekman pumping.