A catalogue and a classification of surface cyclones for the Western Mediterranean

The Mediterranean Sea is a region that possesses a high frequency of cyclon es. Many of them are lee depressions and so, mesoscale and weak, but others are strong and cover a wide area. In this study some characteristics of su rface cyclones in the Western Mediterranean are presented. First a database was built from hand analyses of sea-level pressure from 1992 to 1995. Next , a similar database was obtained from the LAM-INM (Limited Area Model of t he Institute Nacional de Meteorologia of Spain) objective analyses of the 1 000 hPa geopotential field. Results show an important increase in the numbe r of cyclones when a mesoscale analysis is carried out. Most of the Western Mediterranean cyclones are mesoscale and weak, and they are not uniformly distributed in space and in time. On the one hand, there are some areas wit h a high concentration of cyclones. The location of some of them, close to the main mountain ranges, suggests their possible orographic origin. On the other hand, in some areas the cyclones are present during the whole year, but in other areas are seasonally distributed. Finally, a study of typologi es of the cyclones was conducted by using the cluster analysis technique. T he classification was performed from the intensity of the cyclones and the shape of the sea-level pressure around the centre. Results are similar from both databases and so the existence of seven typologies have been identifi ed. Copyright (C) 2000 Royal Meteorological Society.