Iarova D. Quasitropical cyclone over the Black Sea (numerical modeling and data analysis)

An anomalously intensive cyclone that formed over the Black Sea in September 2005 is studied. It is shown that according to its main physical properties and energy supply mechanisms, the cyclone can be regarded as a quasitropical one. In particular, the impact of the atmospheric cyclone on the Black Sea was similar to the impact of a tropical cyclone on the ocean. It is found that favorable conditions for the development of the Black Sea quasitropical cyclone were as follows: 1) large reservoir of convective potential available energy, 2) background convergence in the low layer of the atmosphere, 3) absence of strong wind, and especially absence of vertical wind shear. An additional important favourable factor was a large overheating of the sea surface relative to the surrounding land.General characteristics of the Black Sea cyclone, its evolution and physical formation mechanisms are studied. By analyzing the vortex's radial, azimuthal and vertical momentum budgets it is shown that the cyclone was a fairly balanced system at a mature stage as hydrostatic and gradient balances were valid. With the help of numerical experiments it is shown that air-sea interaction played an important role in the Black Sea cyclone development, which means another similarity to a tropical hurricane.Climatic frequency of quasitropical cyclones in the Black Sea Region is also studied. It is found that such cyclones are rear phenomena for the region as, according to the analysis performed over a 40-year period, there were only several vortexes over the sea, whose kinematical structure was similar to that of a quasitropical cyclone.