The general circulation models used to simulate global climate typically feature resolution too coarse to reproduce many smaller-scale processes, which are crucial to determining the regional responses to climate change. A novel approach to downscale climate change scenarios is presented which includes the interactions between the North Atlantic Ocean and the European shelves as well as their impact on the North Atlantic and European climate. The goal of this paper is to introduce the global ocean-regional atmosphere coupling concept and to show the potential benefits of this model system to simulate present-day climate. A global ocean-sea ice-marine biogeochemistry model (MPIOM/HAMOCC) with regionally high horizontal resolution is coupled to an atmospheric regional model (REMO) and global terrestrial hydrology model (HD) via the OASIS coupler. Moreover, results obtained with ROM using NCEP/NCAR reanalysis and ECHAM5/MPIOM CMIP3 historical simulations as boundary conditions are presented and discussed for the North Atlantic and North European region. The validation of all the model components, i.e., ocean, atmosphere, terrestrial hydrology, and ocean biogeochemistry is performed and discussed. The careful and detailed validation of ROM provides evidence that the proposed model system improves the simulation of many aspects of the regional climate, remarkably the ocean, even though some biases persist in other model components, thus leaving potential for future improvement. We conclude that ROM is a powerful tool to estimate possible impacts of climate change on the regional scale.

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influenced by ocean-atmosphere interactions in coupled runs. The strong SST austral summer biases are associated with a weaker SAA, which weakens the winds over the southeastern tropical Atlantic, deepens the thermocline and prevents the local coastal upwelling of colder water. The biases in the basins interior in this season could be related to the advection and eddy transport of the coastal warm anomalies. In winter, the deeper thermocline and atmospheric fluxes are probably the main biases sources. Biases in incoming solar radiation and thus cloudiness seem to be a secondary effect only observed in austral winter. We conclude that the external prescription of the SAA south of 20°S improves the simulation of the seasonal cycle over the tropical Atlantic, revealing the fundamental role of this anticyclone in shaping the climate over this region.

a b s t r a c tThe generation of large-amplitude internal waves in the Strait of Gibraltar is a widely known phenomenon. Those waves are produced by the interaction of barotropic tidal flow with the main sill (Camarinal Sill) topography and the stratified water column. That interaction primarily causes internal tides that evolve, by non-linear processes, into large-amplitude (more than 100 m) internal waves exhibiting much shorter oscillation periods than those related to the basic tidal variability. Recent observations have shown that on many occasions large-amplitude internal wave generation is dependent on the state of the subinertial flows, which are basically driven by the atmospheric pressure fluctuations over the Mediterranean. Therefore, depending on the meteorological situation over the Mediterranean, internal wave events may be inhibited or activated.

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Abstract. The M 2 and S2 surface tides in the Strait of Gibraltar are simulated using a two-dimensional, nonlinear, boundary-fitted coordinate model with a nominal resolution of -0.5 km. Good agreement is achieved with tide gauge and bottom pressure observations, as well as with current measurements made during the Gibraltar Experiment. The cotidal charts and the maps of tidal current ellipse parameters, which have been constructed on the basis of the model results, reproduce all of the known features of the spatial structure of the M 2 and S2 tidal waves. These results also show that a -90 ø phase difference between tidal velocity and elevation is detected in much of the Strait of Gibraltar, thus suggesting a small mean tidal energy flux through the strait. The model results give evidence of the general direction for the M 2 and S2 net tidal energy fluxes to the west. This finding is consistent with an observed southwestern tidal phase propagation and remains qualitatively unchanged when varying the strait's geometry as well as boundary and astronomical forcings. We have already mentioned topographic funnelling, which may be responsible for a nearly 90 ø phase difference between tidal velocity and elevation. This subject merits closer attention. Topographic funnelling (a term introduced by Jay [1991]) is defined as the direct dependence of tidal characteristics on the geometry of a channel. As was stated first by Hunt [1964] and thereafter by Jay [1991] and Friedrichs and Aubrey [1994], the nature of tidal waves in strongly convergent channels with friction is fundamentally different from that of classical damped tidal co-oscillations. This means that in a channel of uniform width and depth, an incident wave produces a 90 ø phase difference between tidal velocity and elevation only when it interacts with a reflected wave of nearly equal amplitude, in contrast to a channel with an exponential change in cross-sectional area, where the same incident wave can produce an identical phase difference without the presence of a reflected wave.Jay [1991] analyzed the asymptotic cases of weak convergence (friction and changes in geometry are weak relative to the acceleration), strong convergence (friction and acceleration are weak relative to the effect of geometry), critical convergence (acceleration and geometry effects are equal and of opposite sign), and supercritical convergence (strong changes in geometry with weak friction). He showed that the phase difference in exponentially convergent channels was -0 ø just 13,541

Abstract. We analyze the climate change signal in the Mediterranean Sea using the regionally coupled model REMO–OASIS–MPIOM (ROM; abbreviated from the regional atmosphere model, the OASIS3 coupler and the Max Planck Institute Ocean Model). The ROM oceanic component is global with regionally high horizontal resolution in the Mediterranean Sea so that the water exchanges with the adjacent North Atlantic and Black Sea are explicitly simulated. Simulations forced by ERA-Interim show an accurate representation of the present Mediterranean climate. Our analysis of the RCP8.5 (representative concentration pathway) scenario using the Max Planck Institute Earth System Model shows that the Mediterranean waters will be warmer and saltier throughout most of the basin by the end of this century. In the upper ocean layer, temperature is projected to have a mean increase of 2.7 ∘C, while the mean salinity will increase by 0.2 psu, presenting a decreasing trend in the western Mediterranean in contrast to the rest of the basin. The warming initially takes place at the surface and propagates gradually to deeper layers. Hydrographic changes have an impact on intermediate water characteristics, potentially affecting the Mediterranean thermohaline circulation in the future.