A 44-year (1958-2001) high-resolution atmospheric hindcast for the whole Mediterranean Basin was performed within the EU-funded Hindcast of Dynamic Processes of the Ocean and Coastal Areas of Europe (HIPOCAS) Project. The long-term hindcasted data set, which comprises several atmospheric parameters at different levels, was produced by means of dynamical downscaling from the NCEP/NCAR global reanalysis using the atmospheric limited area model REMO. The REMO hindcast has been exhaustively validated. On that score, various hindcasted surface parameters, such as 10-m wind field, 2-m temperature and mean sea level pressure, have been compared to satellite data (ERS-1/2 scatterometer) and in-situ measurements from offshore stations. In addition, two ocean models (waves and sea level) have been forced with REMO hindcasted fields (mean sea level pressure and 10-m wind field). The validation of these ocean runs, performed through comparisons of simulated waves and sea level with oceanographic measurements, allows to evaluate "indirectly" the quality of the REMO hindcasted data used as atmospheric forcing. Once the quality of the hindcasted data was verified, the efficiency of the regional enhancement performed through dynamical downscaling on the NCEP global reanalysis was assessed. The regional improvement was evaluated through comparisons of REMO and NCEP performance in reproducing observations. The important improvement obtained in the characterization of extreme wind events is particularly remarkable.

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[1] Current meter observations collected within Canary Azores Gibraltar Observations (CANIGO) project have been analyzed in order to study subinertial flows through the Strait of Gibraltar. Estimated net flow has been compared with hindcasts provided by Nivmar Prediction System-Hamburg Shelf Ocean Model (HAMSOM) circulation model forced by wind stress and atmospheric pressure applied to the North Atlantic Ocean and the Mediterranean Sea. The model was first run-forced by atmospheric pressure and then by atmospheric pressure and wind stress in order to assess the relative importance of each external agent on the subinertial flow. The main driving force is the atmospheric pressure over the Mediterranean Sea, although wind stress in the Atlantic side of the strait may contribute appreciably to subinertial net flow. Inflow variations account for 60% of the subinertial variability approximately. The interface depth correlates well with the net flow fluctuations, sinking or rising under positive (toward the Mediterranean) or negative fluctuations, respectively, with an average gain of around À60 m/Sv. These results have been interpreted in the scope of the hydraulic two-layer theory to conclude that the exchange is submaximal rather than maximal. Salinity on the interface increases (decreases) for positive (negative) net flow fluctuations. This is explained in terms of increased (decreased) recirculation of water from the passive Mediterranean layer driven by the velocity changes that atmospheric forcing induces in the active Atlantic layer. The contribution of the recirculated water to the fluctuations of the net flow is of secondary importance (around 5% on average), but the layer that recirculates may be thicker than 50 m, what could have important biological implications.

[1] We use the trajectory of three buoys dragged below the surface mixed layer, together with sea surface temperature imagery, to examine the evolution of an anticyclonic warm-core eddy since its generation by the Canary Islands. Two buoys remain within the eddy during some 100 days, and the third one remains almost 200 days, while drifting southwestward up to 500 km with the mean Canary Current. The eddy merges with several younger anticyclonic and cyclonic eddies, in each occasion, suffering substantial changes. The eddy core, defined as a region with near-solid-body-type rotation and radial convergence, initially occupies the whole eddy. After interacting with another vortex the inner core markedly slows down, although it continues displaying radial convergence and relatively small radial oscillations, and an uncoupled outer ring is formed or enhanced, which revolves even more slowly and displays large radial fluctuations. The vortex extensive life is consistent with its inertially stable character and observations of radial convergence. A very simple model of vortex merging, where cylinders fuse conserving mass and angular momentum, gives fair results. The observations suggest that the eddy changes, as the result of its own slow evolution and sporadic mixing events, from a young stage, where the core retains its vorticity and occupies most of the eddy, through a mature stage, where the eddy has a reduced inner core and a slowly revolving outer ring, to a decay stage, where the vorticity maximum is substantially reduced.

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