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Abstract: The Mediterranean basin features a semi-enclosed sea, where interactions and feedbacks between the atmosphere and the Sea at various temporal and spatial scales play a predominant role in the regional climate. This study analyzes the Mediterranean Sea response in sensitivity experiments conducted by driving the NEMO-MED12 oceanic model in perpetual mode with various atmospheric forcings, all produced by the WRF non-hydrostatic mesoscale atmospheric model, but differing by their resolutions: two horizontal resolutions (20km at basin scale and 6.7km in the North-Western [NWE] area) and two temporal resolutions (daily and three-hourly). The atmospheric fields available from August 1998 to July 1999 are in good agreement with estimates derived from satellite data. The heat budget of the Mediterranean Sea represents an heat loss of 5W/m2 and the annual freshwater budget is −1.04m, in agreement with climatologies. An increase in the spatial resolution in the NWE area modifies the modeled circulation from −10% to +15% for the SST, from −30% to +50% for the SSS, from −10% to +30% for the MLD and from −10% to +30% for the EKE in surface. The increase in the wind speed with a better chanelling by the land orography enhances in particular the oceanic convection process in the NWE area. On the other hand, the increase in the temporal resolution reduces the convection process, because of the diurnal restratification of the oceanic upper layer. It also reduces the surface parameters high-frequency variability, whereas it increases the EKE values in surface, due to the rapid response to the wind. [Copyright &y& Elsevier]

Abstract: Within the framework of several local and international programs, a quasi-operational ocean-forecasting system for the Southeastern Mediterranean Sea has been established and evaluated through a series of preoperational tests. The Princeton Ocean Model (POM) is used for simulating and predicting the hydrodynamics while the Wave Model (WAM) is used for predicting surface waves. Both models were set up to allow varying resolution and multiple nesting. In addition, POM was set up to be easily relocatable to allow rapid deployment of the model for any region of interest within the Mediterranean Sea. A common requirement for both models is the need for atmospheric forcing. Both models require time varying wind or wind stress. In addition, the hydrodynamic model requires initial conditions as well as time dependent surface heat fluxes, fresh water flux, and lateral boundary conditions at the open boundaries. Several sources of atmospheric forcing have been assessed based on their availability and their impact on the quality of the ocean models'' forecasts. The various sources include operational forecast centers, other research centers, as well as running an in-house regional atmospheric model. For surface waves, higher spatial and temporal resolution of the winds plays a central role in improving the forecasts in terms of significant wave height and the timing of various high wave events. For the hydrodynamics, using the predicted wind stress and heat fluxes directly from an atmospheric model can potentially produce short range ocean forecasts that are nearly as good as hindcasts forced with gridded atmospheric analyses. Finally, a high-resolution, nested version of the model has shown to be stable under a variety of forcing conditions and time scales, thus indicating the robustness of the selected nesting strategy. For the southeastern corner of the Mediterranean, at forecast lead times of up to 4 days the high-resolution model shows improved skill over the coarser resolution driving model when compared to satellite derived sea surface temperatures. Most of the error appears to be due to the analysis error inherent in the initial conditions. [Copyright &y& Elsevier]

The interannual variability of the Mediterranean (MED) circulation from 1979 to 1993 is studied with a 1°/8×1°/8×1°/8 resolution OGCM. The surface forcing used is 6 hourly ECMWF (European Center for Medium Range Weather Forecast) reanalysis data. Two different periods in the surface forcing and model variability are identified during 1981–1993: the first, Period I (1981–1987) and the second, Period II (1988–1993). Changes in the model response between the two periods are driven by corresponding differences in the surface forcing, which presumably are a result of the decadal scale changes of the Northern Hemisphere (NH) atmospheric regimes, related to the intensification of North Atlantic Oscillation (NAO) at the end of the 1980s.During the second period (1988–1993), the Mediterranean circulation reveals an overall weakening of the kinetic energy in the Western Mediterranean (WMED) basin and significant changes in the structure of circulation in the Eastern basin. In the latter region, the anticyclonic activity increases in the southern Ionian and in the southern area of the mid-Mediterranean Jet. These anticyclonic eddies, present during different years of Period II with variable intensity, have an important impact on the transport of Modified Atlantic Waters (MAW) and Levantine Intermediate Waters (LIW) in the Eastern Mediterranean (EMED). This change of the circulation modified the salinity and the amount of Levantine Intermediate Waters transported towards the Aegean Sea and the Adriatic Sea, which are important factors for deep water formation processes there. These model results are in good agreement with available observational results. The deep water formation event observed in the Aegean Sea [Science 271 (1996) 333] is produced by the model, but at a shallower depth. We interpret this event as the result of circulation changes between Period I and Period II and anomalous surface atmospheric forcing over the Aegean Sea. [Copyright &y& Elsevier]