A phenomenological definition of "medicane"

Vortices with visual characteristics typical of tropical cyclones, such as cloudless eye-like features surrounded by spiraling clouds and rainbands, are occasionally observed in the Mediterranean. These systems form a peculiar subcategory of Mediterranean cyclones, known in the scientific literature as medicanes (a portmanteau of the words “Mediterranean hurricanes”). Despite their limited number (about 1-3 events per year), medicanes are directly related with high impact weather (e.g., strong wind gusts, high sea waves, and heavy precipitation) and thus have been constantly attracting the interests of both the scientific community and the general public.

Unfortunately, the term “Mediterranean tropical cyclone” or “medicane” has been used in different ways by different authors. Some definitions are based on visual features detected in satellite imagery, others on structural characteristics derived by diagnostics applied to numerical weather prediction outputs. The absence of an official or commonly accepted definition has created some confusion within the scientific and weather forecaster community. Moreover, recent case studies on the dynamics of several systems widely recognized as medicanes show different underlying development mechanisms.

Following the outcomes of two recent projects (“MedCyclones”, supported by COST–European Cooperation in Science and Technology, and “MEDICANES”, supported by the European Space Agency), a phenomenological definition of “medicane” was proposed, which is based solely upon earth observations and accommodates the cases analyzed so far in previous studies. This commonly agreed definition is necessary to assess their climatology in past and future climate, as well as to objectively identify such systems in weather forecasts.