Tropicalization process of the 7 November 2014 mediterranean cyclone: numerical sensitivity study

Abstract

Tropical-like Mediterranean cyclones (medicanes) have been documented and investigated in the literature, revealing that theirphysical mechanisms are stillpoorly understoodand likely not unique across cases. During late hours of 7 November 2014 a small-scale cyclone was detected over the Sicilian channel, affecting the Islands of Lampedusa, Pantelleria and Malta. Gust wind values exceeding 42.7m s-1and a pressure drop above 20 hPa in 6 hours were registered in Malta. Clear signatures of a well-defined cloud-free eye surroundedwithconvective activity of axisymmetric character were identifiable through IR satellite imagery during the late stages of the cyclone, resembling the properties of a hurricane.Weinvestigate the cyclogenesis and posterior development of this small-scale cyclone as well as its physical nature; to thisaim,a set of high-resolution sensitivity numerical experiments were performed. Hart’s phase diagrams adapted to the Mediterranean region clearly reveal the tropical characteristics of the simulated storm. A numerical sensitivity analysis by means of a factor separation technique is used to gain quantitative insight on the roleslatent heat release, surface heat fluxes and upper-level PV signatures (dynamically isolated through a PV-Inversion technique) have on the unfold of this singular event. Results show the importance of the upper-level dynamics to generate a baroclinic environment prone to surface cyclogenesis and in supporting the posterior tropicalization of the system. On the contrary, latent heat release and surface heat fluxes factors do not seem to contribute, as individual processes, tothe genesis of the cyclone as much as it could be suspected, considering itbehavesas a tropical-like cyclone. However, the asynchronous synergism between latent heat release and PV factors plays a crucial role for the intensification of the cyclone towards reaching the pure diabatic phase.