Air-sea interaction and straits exchanges in the Mediterranean Sea
© Boukthir Moncef, Abdennadher Jihene
Total heat budget and freshwater flux at the surface of the Mediterranean Sea as well as their seasonal and inter-annual variations are examined using 15-year of ECMWF fields. In addition, water exchanges through the Straits of Gibraltar and Sicily are also investigated. As for all previous estimates, we found an imbalance in the total heat budget by the amount of 10 W m-2. Nevertheless, this uncertainty is not large compared to previous estimates. The water budget reveals an annual mean freshwater deficit in the Mediterranean of 48 cm/year, lower than some previous estimates. We attribute these uncertainties to an underestimation of the latent heat flux. Net heat flux is characterised by a strong seasonal cycle and the major contribution comes mainly from the latent heat. There is a net heating of the Mediterranean during March - September period, the rest of the year is characterised by net cooling. The net water transports through the straits of Gibraltar and Sicily deduced from net evaporation show an important seasonal cycle. The amplitude of the water transport through Gibraltar strait, which exceeds that through Sicily strait, is comparable to other independent estimates. On the other hand, the inter-annual variation seems to be less important. This suggests the dominant role of net evaporation in controlling the annual cycle of water transport through the straits. High-frequency fluctuations observed in net water transports through the straits seem to be mainly governed by atmospheric pressure fluctuations. Despite the bias observed in net heat and freshwater fluxes, the ECMWF data provide valuable information about their seasonal and inter-annual variability.