On the Tropical Nature of an Intense Mediterranean Cyclone in the Ocean-Atmosphere System

The Mediterranean basin hosts a large number of cyclones every year. Among them, some rare cases named medicanes present similarities with tropical cyclones but their dynamical characteristics are debated. The ocean-atmosphere dynamics of Medicane Ianos (2020) are studied here through km-scale fully coupled ocean-wave-atmosphere simulations. These allow investigating the tropical nature of Ianos in terms of both atmospheric circulation and thermal structure, and of oceanic cold wake response which feedbacks negatively onto the cyclone's intensity. Simulations match in situ and remotely sensed observations in the ocean and atmosphere well. Three life cycle phases can be distinguished with a central phase during which the cyclone is compact and axisymmetric. Orographic acceleration is shown to induce asymmetry in the cyclonic winds and precipitation prior to landfall. These are expected to be common for medicanes given the small scale and steep orography of the Mediterranean basin. Ianos distinguishes itself from previous medicanes by its intense cold wake wherein the sea surface cooling exceeds 3°C. The wake results mainly from mixing at the base of the mixed layer, while surface fluxes play a secondary role as revealed by temperature budget analysis. The amplitude and dynamics of the wake are alike those found in tropical cyclones of category 2 or higher. A deep warm core cyclonic eddy on Ianos' track is responsible for an interruption in the cold wake which coincides with the re-intensification of the cyclone during its central phase. Such eddies are widespread in the Mediterranean but poorly constrained in models.