Climatology of Mediterranean cyclones using the ERA-40 dataset

The generation of cyclone climatologies has recently received a renewed interest. Cyclones are closely related to the climate of certain regions, and thus, their variability is one of the key points in current climate research. The Mediterranean is a region with high density of cyclones, but due to its location and its particular morphology, cyclones are subject to large spatial and seasonal variability. Moreover, some cyclones are related to hazardous weather events, in particular, heavy precipitation and strong winds. Improved knowledge of Mediterranean cyclones would contribute to the improvement of the forecasts of such damaging events. In this study, objective detection and tracking algorithms are used on the ERA-40 reanalysis to derive a climatology of surface cyclones for the Mediterranean region. The detection algorithm is also applied at various vertical levels, characterizing the three-dimensional structure of the cyclones, and allowing to derive their vertical thickness. The relatively high spatial resolution, but mainly the long period (45 years) makes the ERA-40 reanalysis especially suitable for the generation of a cyclone climatology. The aim of this study is twofold. First, a detailed description of the Mediterranean surface cyclones is obtained. This includes the spatial and seasonal variability and some of their main individual features, like the intensity, size, vertical thickness and life cycle. Moreover, some regions with a large cyclogenetic frequency are studied in detail. Second, the results of the present climatology are compared with many other studies. The qualitative comparison indicates a general agreement with most of previous climatologies. However, as a consequence of the ERA-40 resolution, the comparison with high-resolution cyclone datasets shows a shortcoming related to the detection of small cyclones. Nevertheless, it is concluded that the current climatology depicts a comprehensive view of the synoptic and sub-synoptic cyclonic activities in the Mediterranean. Copyright (C) 2010 Royal Meteorological Society