Christos Lamaris

The objective of this study is the evaluation of the physical processes responsible for the genesis and evolution of an explosive cyclone in the central Mediterranean with the aid of the surface pressure tendency equation. For this reason, the equation is solved numerically, providing the opportunity to quantitatively specify the relative significance of the diabatic processes in Mediterranean explosive cyclogenesis, contrary to the qualitative approach of previous studies. Our approach allows for the first time a direct comparison of the physical mechanisms between the cyclogenesis over the northern and the southern part of the central Mediterranean. The results demonstrate that the interaction between the upper level baroclinic and low-level diabatic processes triggered the development of the explosive cyclone, but low-level baroclinicity and diabatic processes prevailed during the cyclone evolution.

This study investigates the dynamics of the development phases of a Mediterranean tropical-like cyclone (medicane) in the southern Ionian Sea, on 28 September 2018 that caused high impact phenomena in the central and eastern Mediterranean, focusing on the transition from explosive cyclone to medicane. The symmetry and the warm core structure of the system have been demonstrated via phase space diagrams determining three phases of the system development that are then supported on a dynamical basis. During the first phase of the system, baroclinic instability triggered the formation of the explosive cyclone, when strong upper-level PV anomalies at the dynamic tropopause level moved towards a pre-existed area of enhanced low-level baroclinicity over the coastal areas of Libya along with positive SST anomalies. The surface frontal structure was enhanced under the influence of the upper-level dynamic processes. During the second phase when the medicane formed, low-level diabatic processes determined the evolution of the surface cyclone, without any significant support from baroclinic processes in the upper troposphere. The distortion of the low-level baroclinicity and the frontal structure began after the initial weakening of the upper-level dynamics. During the third phase, the system remained barotropic, being affected by similar mechanisms as in the second phase but with lower intensity. The transition mechanism is not only the result of the seclusion of warm air in the cyclone core but, mainly, the continuation of an explosive cyclone or an intense cyclone when the occlusion began to form.