A case study diagnosis of Cyclogenesis over the Black Sea

In this study, cyclogenesis was investigated over the Black Sea from synoptic-dynamic view. While the Black Sea has an important role in precipitation of northwest of Iran, a system that is formed over the Black Sea was selected and it affected Iran on ۱۴th and ۱۵th March ۲۰۰۹ (۴۰ mm precipitation has occurred in some stations). Using archived data of NCEP / NCAR, absolute and thermal vorticity advection in ۵۰۰hPa level and potential vorticity at ۳۲۵ degrees Kelvin level were calculated. Within the development process the cutoff low was formed over the Black Sea and the difference between directions of the upper-level cutoff low at ۲۵۰hPa level and surface low represents a strong baroclinicity which in turn supports cyclogenesis. The results show that the absolute and thermal vorticity advection in mid-level and potential vorticity anomaly has a fundamental role in creating cyclogenesis. In such a way that the absolute vorticity advection gets ۱۵ times larger (about ), and cyclogenesis occurs when the mid-level trough axis is altered from northeast-southwest direction to northwest-southeast direction, and the polar jet will be combined with a subtropical jet. Also, a strong dependence of the cyclogenesis in initial stages occurs when a large upper level Potential Vorticity (PV) anomaly advected into a region where there is a meridional potential temperature gradient at low-level.

Keywords:

potential vorticity , NCEP/NCAR , Heavy precipitation , Dynamic meteorology , Iran