Medicanes: cataloguing criteria and exploration of meteorological environments

Abstract

Depressions with a similar structure to tropical cyclones, that can reach the intensity of hurricanes, are occasionally generated in the Mediterranean. Such phenomena are called “medicanes”. Although the geographical dimensions of tropical oceans and the Mediterranean Sea are clearly different, the precursor mechanisms of these perturbations, based on the air-sea thermodynamic imbalance, are similar. This fact made us think about the existence of a physical parallelism between both phenomena. We tried to identify such cases from historical images of the Meteosat satellite, for the period 1982-2005. Different lists have been created, each of them increasingly delimiting the selection criteria based on the cyclone structure in the infrared channel. Some of these criteria are, for instance, the size of the cyclone, the clear existence of an eye and the lifetime of the system. This identification has been made in a subjective way. In total, twelve cases of medicanes were identified. The characterization of meteorological environments that are a precursor to medicanes can help us understand the genesis mechanisms and to improve forecasts. This study compares the values of several meteorological variables of interest in the cases of medicanes with those of cyclones catalogued in the database of the MEDEX project to try to identify the environments that favor the genesis and development of medicanes instead of other Mediterranean cyclones. In this sense, the sea surface temperature, the diabatic contribution to the local trend of surface equivalent potential temperature and an empirical index derived from the genesis of tropical cyclones are presented as possible discriminatory parameters.