Surface heat fluxes influence on medicane trajectories and intensification

A few tropical-like cyclones have developed over the Mediterranean Sea during the last decades according to the inventory of images provided by Meteosat satellite. These extreme small-scale warm-core storms, also called “medicanes”, operate on the thermodynamical disequilibrium between the sea and the atmosphere, and sometimes attain hurricane intensity and threaten the islands and coastal regions.Despite their small size, mesoscale model runs at moderate horizontal resolutions (7.5 km) made with MM5 are able to simulate the formation of a subsynoptic cyclone and the general trajectory of the disturbance, and for most of the cases a warm-core axi-symmetrical structure becomes evident in the simulations. The timing and precise details of the storm trajectories are shown to be more problematic when compared against the satellite images available for the events. It is hypothesized that the small size of the systems and the crucial role of moist microphysics, deep convection and boundary layer parameterizations are the main factors behind these errors. On the other hand, a sensitivity analysis examining the role of the sea surface heat fluxes is conducted: latent and sensible heat fluxes from the Mediterranean are switched off at the beginning of the simulations to explore the effects of these factors on the medicane trajectories and deepening rate.Results show different roles of the surface heat fluxes on medicane properties (intensification and track) depending on their magnitude and spatial distribution over the Mediterranean Sea. In this way, three distinct patterns have been identified using a database of twelve events.

► We numerically simulate hurricane-like Mediterranean storms ("Medicanes") with overall good results. ► We perform additional tests aimed at isolating the role of surface latent and sensible heat fluxes from the Mediterranean Sea. ► Different relative importance of surface fluxes on storm intensification and trajectory are identified depending on the case. ► Medicane track in relation with the zones of largest sea-atmosphere moist enthalpy disequilibrium is a cricial factor.