Abstract EN:

The aim is to study the genesis and evolution of storms on the western part of the black sea from 1974 to-1993. Storm is defined by i) wind speed higher that 12 m/s and ii) waves between 1. 25-2. 50 m. The 185 storms are more frequent from october to april. The 3 types are identified through the location of atmospheric centers at sea level. The 1-st type (>52%) is the couple anticyclone/depression (with travelling disturbances from the mediterranean sea to the black sea). The continental anticyclone and the mediterranean depression extending northeastward create a strong pressure gradient. The thermal contrast between the cold and dry continental air and the warm and humid maritime air intensify the winds, which are dominantly north. The 2-nd type - storms in anticyclonic situation (>24%) - are created in a high pressure field (with presence of mediterranean disturbance or with lowering pressure on the eastern part of the black sea). The n-ne strong winds at the periphery of the continental anticyclones blow along the romanian coast. In the middle troposphere, the ridge previously located over western europe moves to se and reinforces the anticyclone at the surface. Local higher surface temperatures and cold advection on the western part of the sea favour lowering of pressure on the eastern part. Cold troughs in middle troposphere reinforces the cyclogenesis which then looks like the 1-st type. Storms in low pressure field (@19%) are the consequence of travelling low pressure systems from the atlantic or from the mediterranean sea to the black sea. Winds blow from various directions, but the strongest are the n ones. These storms are weaker than the 1-st and the 2-nd type. This typology could help to prevent navigation risks associated with these storms (strongly correlated with navigation accidents near the romanian shore).