Synoptic aspects associated with pervasive dust storms in the southwestern regions of Iran

Dust storm is a natural hazardous phenomenon that affects arid and semi-arid regions of the world the same as Iran. The present research aims to investigate the formation of synoptic patterns of pervasive dust storms (PDSs) in the southwestern regions of Iran. For this purpose, daily data of visibility less than 1000m in 16 synoptic stations (Ilam and Khuzestan provinces) were reviewed during 2004-2017, and 59 PDSs with more than 2 days of duration (overlapped: 70% of the region) were extracted. In practice, mid-level atmospheric data (500, 700, 850 hPa, and sea level pressure (SLP)) with 2.5*2.5 degree resolution (domain: 0-80 degrees E and 10-70 degrees N) were obtained from NCEP/NCAR reanalysis dataset, and the matrix 825*59 of 500 hPa data was performed. Principal component analysis (PCA) with S-mod, were used for extracting synoptic patterns that make PDSs. PCA showed that the first four components ensured more than 86.45% of the data variance. PDSs classification based on output components showed that the patterns had seasonal structures. Synoptically, the north wind blowing in the first pattern is the most dominant structure in the formation of PDSs in the Middle East. The second and third patterns showed postfrontal structures. The fourth pattern with prefrontal structure was the reason for PDSs in the cold seasons of the year. From the four final patterns, the first three patterns showed the dominance of the Persian trough in the SLP maps. Mean values map analysis of the aerosol optical depth suggests that each of the most consistent synoptic patterns stimulates special dust centers.