Geographical Research

In this research، the correlation between precipitation change in Southern coasts of Caspian Sea and variability of sea level pressure have been analyzed by using environmental to circulation approach at time period 1339- 1383. In this respect، we make use of daily precipitation data of the 12 synoptic stations of studied area at surface data base section and prepare the time series matrix of precipitation days. About atmospheric data base، we made use of sea level pressure(slp) data which are available on data base NCEP/NCAR at 0° to 120° E and 0° to 80° N. Then، we prepared primary matrix including the daily precipitation values of every station and average values of sea level daily pressure which is consistent with time series of precipitation days for grid cell (49×33= 1617) at selected area. The calculation of correlation coefficient between daily precipitation values with average values of sea level pressure over studied area cells and drawing the plots for correlation coefficient of precipitation- pressure of stations indicated that precipitation change and occurrence at southern coasts of Caspian Sea in sea level affected by predominance the Caspian، Black Sea and Mediterranean pressure circulation pattern. Hence، precipitation change in Southern coasts of Caspian Sea related to decrease and increase of pressure rate in action field of this pattern

Identification of spatial-temporal anomalies sea level pressure in part of northern hemisphere was the main aim in this research. For this purpose six hourly data used from the to eastern longitude and to northern latitude. In this location، there are 825 pixels to geographical degree. Therefore، database extent created. In this matrix، 825 are number of the pixels at that location and 90520 is number of six hourly scout of the sea level pressure during 62 years (1948-2009). Using these data، monthly anomalies sea level pressure obtained for every pixel. Frequency lesser and higher then long term mean calculated such as the negative and positive anomaly to sequence. For every month anomaly map of the sea level pressure have been drawled. The results showed that frequency of negative anomalies of the sea level pressure، almost during from November to April in most parts of Iran have been more then 50 percent and also during May to October lesser from 50 percent.