Effect of Sea-Air Interaction of Caspian Sea on Heavy and Super Heavy Precipitation Events in the Southern Coasts of Caspian Sea

Abstract

Cloudiness and precipitation are the most important variables contributing to the formation of the climate of the southern coasts of Caspian Sea. The aim of this research is the investigation of the effect of air-sea interaction on the occurrence of the heavy and super heavy precipitation which is caused by convective and non-convective clouds. On the basis of daily precipitations and with regard to 25% and 50% probability, precipitation events are divided into heavy and super heavy and are also grouped into convective and non-convective cases based on the clouds synoptic codes. The maximum of each precipitation event, the mean and the coverage area was calculated using iso-rain maps for each of the four groups. The relationships among the mean of “2 m air temperature minus sea surface temperature (SST)”, SST and precipitation events were studied. The results show that there are three conditions to occur heavy and super heavy precipitation including, SST increasing harmonically from the north to the south of the Caspian Sea, increased mean SST all over the Sea and increased mean of “2 m air temperature minus SST”. The latter detected factor which is the most effective variable is less in convective than non-convective events and in heavy precipitation than in super heavy events.