The role of North Sea - Caspian upper atmospheric teleconnection pattern (NCP) in temporal variability's of rainfall in Sothern coastal of Caspian Sea

The North Sea -Caspian upper atmospheric teleconnection pattern (NCP) is one of very important teleconnection patterns of 500 hecto-pascal level. This teleconnection pattern has important role in implications on the regional climate of Eastern Mediterranean. So far, the role of said pattern on the rainfall fluctuations of southern shores of Caspian Sea has not been studied. Accordingly, in this study the relationship between the patterns of North Sea – Caspian index with Caspian Sea rainfall fluctuations in a long period of 55 years (1955-2010) has been studied. The data used in this study include Monthly rainfall data from five synoptic stations on the southern coast of the Caspian Sea, Data of pattern of North Sea – Caspian index and Re- analyzed Geopotential height data. Results, Show an increase of precipitation in positive phase of the North Sea – Caspian and decrease of precipitation in the negative phase. In the time point of view, correlation coefficients calculated show significant relationship between the rainfall stations and pattern of North Sea – Caspian in April to September. Most of the monthly correlations between stations with 0/555 were calculated in December. Analysis of seasonal Correlation also showed the more influence of rainfall in fall and winter with 0/396 and 0/392 significant correlation coefficients respectively. Gorgan station as Easternmost station in the south Caspian Sea, showed worse correlation with pattern of North Sea – Caspian, and Rainfall Except for February, did not show Correlation with pattern of the North Sea – Caspian in all months and seasons, this is Probably due to the distance of Gorgan station from action center of Caspian sea. Analysis of Atmospheric patterns in level of 500 hPa in positive and negative phase show establishment of a deep trough over the Mediterranean and Placement of Southern shores of the Caspian sea in the East Trough provides Cyclonic condition that Cause transfer of Moisture of north sea, the Mediterranean, Black Sea and the Atlantic Ocean to Iran. However, in negative phase of the study area located below the ridge axis led to barotropic atmosphere with weak zonal wind and Due to the warm and dry air blowing of Africa, rainfall is low in Iran.