Synoptic analysis of Ilam dust storms (1987 - 2005)

Dust storms, one type of dust event, are in most cases the result of turbulent winds, including convective haboobs, which raise large quantities of dust from desert surfaces and reduce visibility to less than 1 km. This dust reaches concentrations in excess of 6000 mg m3 in severe events. The major dust source regions are areas of arid and hyper-arid, with mean annual rainfalls of less than 100 mm. The temporal and spatial investigation of dust storms shows the interference of various factors in their occurrence and expansion. These factors is divided into two groups; environmental and human parameters. The climatic (such as low rainfalls, high evaporation, intense wind, drought and atmospheric general circulation) and geological (for example lithology such as Quarts, Clay, Silicate and feldspar), factors are natural parameters, and factors such as over grassing and crop production, wastage of vegetation, increasing growth of population, battle and political problems are human parameters. Much of the current interest in dust storms relates to their possible role in the systems and subsystems of Earth. Dust loadings may affect air temperatures through the absorption and scattering of solar radiation, may affect cloud formation, and convectional activity, influence sulphur and carbon dioxide levels in the atmosphere, and influence geo-chemistry cycle, soil evolution and desertification. Dust storms are one of the destructive climatic phenomena which are affected by various climatic elements such as pressure, precipitation, wind, temperature and evaporation. These phenomena impose much damages to human health, industrial and agricultural installation, population centers and communication ways. The recognition of source regions, creation and expansion style of dust storms and their relation with atmospheric circulation patterns are fundamental factors in reduction of their damages. In recent decades, trend of dust storms has increased in Iran, specially west and southwest areas. This factor is raised the necessity of dust study in these areas more than before. The aims of this study are the recognition and assessment of atmospheric circulation patterns transferring dust storms, expansion style and their temporal frequency using cluster analyses of 19-year data (from 1987 to 2005) in Ilam region. Therefore, hypotheses and questions of the study have concentrated on the investigation of transferring systems of dust and the description of their temporal and spatial distribution.