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Climatology of sensitivities of intense Mediterranean cyclones

Homar Santaner Víctor

During MEDEX phase I, many efforts were devoted to improve the understanding of the genesis, evolution and prediction of Mediterranean cyclones and high impact weather. One of the objectives of MEDEX was aimed at investigating the regions where the Mediterranean cyclones were most sensitive to. Under an ever increasing societal demand for cost cuts and more precise forecasts, great interest has grown within the operational weather community on the adaptable component of observational networks. Decisions regarding where to deploy new observations of special interest under threatening weather, or regarding permanent changes in observational strategies need support from sensitivity studies that determine areas where the addition of observations would optimally improve the skill of numerical predictions.

MEDEX Phase I documents included the creation of a climatology of sensitivities of severe weather episodes in the Mediterranean. The main challenge of these types of studies is the classification of events when no exhaustive and systematized database of Mediterranean high-impact weather episodes exists. Various approaches are explored to build the climatology of sensitivities. A first attempt makes use of the link between Mediterranean hazardous weather and intense cyclones. An objective classification of the most intense Mediterranean cyclones from the ECMWF ERA40 analysis is performed and sensitivities are computed for each group making use of an adjoint model and resulting in a prototype sensitivity field for each class of Mediterranean intense cyclone.

The results show that although the sensitive areas computed for the intense cyclones are not particularly confined, it is remarkable how regions poorly sampled by the regular observing networks, such as North Africa, the Mediterranean sea and the eastern North-Atlantic, are highlighted in the resulting climatological sensitivity maps.

However, an important portion of the hazardous events in the Mediterranean basin are not linked to significantly intense cyclones. For these cases, alternatives based on different proxies for threatening weather are discussed.