Variations of 500 hPa flow patterns over Iran and surrounding areas and their relationship with the climate of Iran

In order to explore the spatial and temporal variations of 500 hPa flow patterns and their relationship with the climate of Iran, monthly mean geopotential heights for the region 0degrees E to 70degrees E and 20degrees N to 50degrees N, at 5 degree resolution, were analysed. The study period covered the winter months October to March during the period 1961-90. The monthly height of the 500 hPa level was averaged along each meridian from 25degrees N to 45degrees N. The height of the mean monthly pressure pattern was mapped against the study years. The results showed that the characteristics of the 500 hPa flow pattern varied over monthly and annual time scales. Principal Component Analysis, with S-mode and Varimax rotation, was also used to reduce the gridded data to 5 (6 in October) significant factors. The factor scores for each month were then correlated with monthly Z-scores of precipitation and temperature anomalies over Iran. The results showed that troughs and ridges located close to Iran had more influence on the climate of Iran. Two troughs were identified and named the Caspian and Syrian troughs.