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Cyclones, strong winds and orography in the Mediterranean

Buzzi Andrea

Mediterranean cyclones and strong winds are strongly correlated, and both phenomena are dynamically associated with the complex orography that surrounds the area. Cyclones can be generated in the Mediterranean or, much more frequently, arrive from adjacent areas but are deeply modified - most often intensified - by local topography and surface fluxes. A number of dynamical processes, related to the presence of orography, have been identified as acting in Mediterranean meteorology, among which are the orographic modification of baroclinic waves/eddies ("lee cyclogenesis"), the reinforcement of the low level winds due to channelling (Mistral, Sirocco etc.), upstream blocking/deviation ("barrier winds") or downslope effects (foehn, Bora etc...). Such processes strongly depend on the intensity and direction of the large scale wind and, noticeably, on the air stratification. Diabatic processes, like those associated with latent heat release (for example, orographic precipitation) or surface fluxes of heat and moisture (for example, wind induced surface heat exchange - WISHE), have an important role in changing the properties of cyclones, usually intensifying them, and occasionally sustaining the formation of mesoscale vortexes similar to small hurricanes that are recurrently observed over the Mediterranean. The availability of relatively high resolution numerical analyses and the application of different high resolution models has allowed a better understanding of the different processes associated with relatively small scale systems and mesoscale features in the Mediterranean meteorology. Case studies of intense cyclones associated with strong wind in the Mediterranean will be briefly reviewed.