Synoptic Analysis of Extreme Dust Storms in Kermanshah

Dust storms are one of damaging climatic phenomena on the synoptic maps that are affected from the elements of pressure، cloudiness، precipitation، relative humidity، wind، temperature، and evaporation. According to Kermanshah province is one of the areas that is affected by the storms، the aim of this study is synoptic analysis of extreme dust storms in Kermanshah Station in 54-year period (1951-2005). First، the number of extreme dust days was identified according to the horizontal visibility index of 100 meters or less. Then، for recognition of transporting atmospheric system of dust، the synoptic patterns of sea level pressure، 500 hPa geopotential، wind direction، omega، surface temperature and profile of subtropical Jetstream from 1000 to 100 hPa were plotted using climate data of upper and middle atmosphere. The results show that the isoheight lines of 500 hPa geopotential have the west - east orientation in both days، and are condensed in the study area. The SLP maps represent the high pressure systems in the West (Iraq، Syria، Europe and Africa) and low pressure systems in the East (Eastern neighbors) that are the cause of western winds and dust storms. Sea level winds are the northern and western winds in both days. Center of Subtropical Jetstream has been formed in the levels higher than 400 hPa. Its tongues have arrived to the ground surface، and have developed in the latitudes of 50 to 65 degrees. Isothermal maps have a similar pattern in both days، and lines 30 to 36˚C have expanded on Iraq، Syria and Iran. Also، Omega maps indicate the descending motions of the air that increases the dust in the study area.