Geographical Research

Cloudiness and precipitation are the most important variable in the climate of the southern coasts of Caspian Sea. Spreading of Caspian Sea in length of latitude in the North، the existence of Elborze Mountain in the South، are caused that when low pressure pass from area or high pressures are located in the around of Caspian Sea، suitable conditions get ready for generating heavier precipitation in the southern Caspian Sea. The aim of this research is investigation on Air-Sea interaction to produce heavy and super heavy with convective and non-convective sources in the southern coasts of Caspian Sea using SST and 2m air temperature. Based on daily precipitation in seven synoptic stations، super heavy and heavy precipitation events database was formed with regards of 25% and 50% probability (1982 to 2003). These Precipitations were divided into two groups including convective and non-convective on the basis of synoptic codes of clouds. Maximum، mean and coverage area of each precipitation event was calculated based on daily rain maps for each 4 groups. In the other hands، SST and 2m air temperature database has been gotten from www.ncdc.noaa.gov and www.dss.ucar.edu for 719 points on Caspian Sea in 0.25 grid points. Mean of «2m air temperature-SST» called humidity absorption Index. The relationships between this index and SST and precipitation were studied. The results show that there are 3 conditions for generating of heavier precipitation events including Increasing of SST along with good organized SST and gradients from north to south of Caspian Sea، increasing mean SST all over the Sea and increasing of mean of «2mair temperature-SST» (moisture absorption index). This index that is the most important variable has less amount in non-convective than convective events and in super heavy than heavy precipitation events.