Frequency of entrance Mediterranean Cyclones to Iran and Their Impact on Widespread precipitation

The fluctuation of rainfall across the country has created many environmental crises in recent years. In this study, in order to investigate the widespread rainy days of Iran, two groups of data centers including high atmosphere data and ground level data were investigated. The high atmosphere data include: geopotential height (in meters) and sea level pressure (hectopascal) that were gathered from the National Centers for Environmental Prediction of U.S. and National Center for Atmospheric Research (NCEP/NCAR) for the statistical periods of 1363 to 1392 (1986 to 2013) for the area of 10 to 60 degrees north and 40 to 80 degrees east. The ground level data were gathered from interpolated data of daily rain from 2939 stations and 19724 days on cells with the area of 14 in 14 kilometers. To analyze the widespread rainfall of the area based on index, the 25th percentile was chosen. Based on this percentile every time 5 percent of Iran is seeing rain to itself, that day will be chosen as the day with widespread rainfall. The results of this study indicate that based on the trajectory of the transferred cyclones to Iran, any time this trajectory is combined with the Red and Black seas, it will add to their impact and occurrence. When the rainfall occurs, the western and north western regions of Iran experience the same amount of rainfall, while eastern and north eastern regions are hit by weaker cyclones and thus the amount of rainfall is less in these areas.