Study of the models of large-scale atmospheric circulation system model on intesify rainfall in Ardebil plain

Atmospheric circulation is important to determine the surface climate and environment, and affect regional climate and surface features. In this study, to quantify its effect, the classification system, developed by Lamb is applied to obtain circulation information for Ardabil, North West Province in Iran, on a daily basis, and is a method to classify synoptic weather for study area. For that purpose, daily mean sea-level pressure (MSLP) for extreme precipitation days from 1971 to 2007 is used to derive six circulation indices and to provide a circulation catalogue with 27 circulation types. The frequency of circulation types over different periods is computed and described. Five circulation types are most recognised in this study: E, SE, A, C and CSE. The catalogue and the associated indices provide a tool to interpret the regional climate and precipitation, and deal with the linkage between the mean extreme regional precipitations in north western of Iran and the large-scale circulation. Five circulation types E, A, SE, C and CSE are associated with high precipitation and rainy seasons (spring and September) but the most precipitation rate is resulted of cyclone family. Low pressure of north latitudes and central area of Iran with low pressure of gang from Pakistan and India.  SE is almost dominant circulation type over the years. The cold season started from august to march is characterized by frequent directional flows, especially E, SE, A, C and CSE whereas in  warm period (Apr–Aug) SE, NE, AE have  smaller role, especially in July, August and September more frequent flows dominated by SE and E.