Tropicalization process of the 7 November 2014 Mediterranean cyclone: Numerical sensitivity study

• Published in: Atmospheric research 2017-11, Vol.197, p.300-312
• Main Authors: Carrió, D.S., Homar, V., Jansa, A., Romero, R., Picornell, M.A.
• Format: Article
• Language: English
• Subjects: Cyclogenesis; Extra-tropical cyclone; Factor separation; Hart's diagram; Medicane; Potential-vorticity inversion
• ISSN: 0169-8095; 1873-2895
• DOI: 10.1016/j.atmosres.2017.07.018

Tropical-like Mediterranean cyclones (medicanes) have been documented and investigated in the literature, revealing that their physical mechanisms are still poorly understood and 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 42.7ms−1 and a pressure drop above 20hPa in 6h were registered in Malta. Clear signatures of a well-defined cloud-free eye surrounded with convective activity of axisymmetric character were identifiable through IR satellite imagery during the late stages of the cyclone, resembling the properties of a hurricane. We investigate the cyclogenesis and posterior development of this small-scale cyclone as well as its physical nature; to this aim, 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 roles latent 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, to the genesis of the cyclone as much as it could be suspected, considering it behaves as 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. •Physical mechanisms involved in the genesis and evolution of the 7 November 2014 medicane are identified and quantified.•Sensitivity of the medicane development to physical factors are numerically investigated using a high resolution model.•A discussion of the event is made according to the relative contributions of baroclinic and tropical-like processes.