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ABSTRACT: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.

This is the second part (statistical approach) of a work concerning the relationship between heavy rain and cyclonic centres in the western Mediterranean. Using a statistical approach we seek to verify the indirect role of the cyclone centres in locating, triggering or focusing heavy rain: a cyclonic centre –even if neither strong nor deep –may contribute to the low‐level flow organisation and so to the creation or intensification of a low‐level warm and wet current that can feed and sustain convective rain in favourable environmental conditions. The foundation for the statistical approach is several Several databases maintained and updated by the Spanish Institute of Meteorology (INM). These databases of cyclonic centres, heavy rain and strong wind events, and mesoscale convective systems (MCSs), all covering the western Mediterranean or part thereof, can be cross‐referenced by looking for simultaneity between heavy rain events (or MCSs) and cyclone centres in the vicinity. We have found that in most of the heavy rain events (around 90%) there is a cyclonic centre in the vicinity, usually located so that its presence favours the creation or intensification of a feeding flow of Mediterranean air towards the area affected by heavy rain. The same occurs with the MCSs. Copyright © 2001 Royal Meteorological Society

An automated procedure has been developed to detect and select mesoscale cyclones and describe their tracks by means of the numerical analysis model, the HIRLAM(INM)-0.5°, operational at the Spanish Institute of Meteorology (INM). This procedure gives us a description of features of these cyclones, such as their frequency of appearance, geographical distribution and horizontal dimensions, and it also enables us to study the movement and the evolution of the cyclone centres. This procedure was developed in order to obtain an automated database of Mediterranean cyclones. To check the performance of this method, the distribution of cyclones was compared with the distribution obtained from a manual catalogue of mesoscale cyclones, and selected cases were studied using both methods. Some results obtained for the western Mediterranean are presented. A large number of cyclones are detected and most of them are located in specific zones, such as the Gulf of Genoa, south of the Pyrenees, south of the Iberian Peninsula and the Alboran Sea. The cyclones follow preferred tracks, which are different depending on the season. Copyright

As many studies reveal, the western Mediterranean exhibits a high frequency of cyclone centres. Most of them are small and weak, but in some cases they are related to heavy rain and/or strong wind events. The climatological study of Mediterranean cyclones is the first crucial step to the better understanding and forecasting of such events.In the present paper, a method to objectively detect and track mean sea-level (MSL) cyclones for the western Mediterranean is described. Furthermore, the three-dimensional characterization of each MSL cyclone is performed by means of several parameters. This includes the vorticity, thermal and humidity fields at different pressure levels where the cyclone is detected, as well as the wind speed profile and the moist stability over the MSL cyclone. Both methodologies are illustrated and validated by a real case: an intense event of the well-known Genoa cyclone. Detection, tracking and three-dimensional characterization are applied to an 8-year (from June 1995 to May 2003) database of numerical analyses. The result is a MSL cyclone database for the western Mediterranean with a description of their threedimensional structure. For a better analysis, cyclones are grouped in three different ways: by thickness, season and region of detection. Results show that western Mediterranean cyclones are located in specific geographical regions and that their location depends on the season. Several cyclones are weak and shallow, mainly because of thermal and/or orographic causes. On the contrary, other cyclones are large and intense and extend throughout the whole troposphere. Differences in cyclone structure depending on the location and season are also discussed.