study of dust storm synoptical patterns in southwest of iran

as widespread deserts is located in west and southwest of iran plateau, dust storms form due to west andsouthwest systems over syria or iraq as well as arabian peninsula. these systems severely affect west and southwestregions. sometimes the fine dusts transmit to central, north east, and east regions. in this study for investigating dustysynoptical patterns, meteorological data at 5 synoptic stations were studied during recent ten years. mean daily sealevel pressure data were selected from the ncep reanalysis data encompassing the region from 20°-60°n latitude by20°-80°e longitude, with a 2.5 spatial resolution and for the 10 year period 1961-2003 in dusty days. selectedterritory is located in a geographical situation that covers all the effecting systems on iran. for classification anddelineate synoptical patterns principal component analysis (pca) and clustering method were used. results showedthat in this region, days with dust have three general circulation patterns. analyzing these patterns show that there isa trough which restricted to 30-45°e longitude in 850 hpa chart, and at least one relatively strong low pressure overarabian peninsula in sea level pressure extending to the west, south west and the study region. this study shows thatabove aspects are the major specifications of dusty days.