Classification of weather clusters over the Middle East associated with high atmospheric dust-AODs in West Iran.

Daily aerosol optical depth (AOD) and meteorological fields obtained from Monitoring Atmospheric Composition and Climate (MACC) and ERA-Interim reanalysis, respectively are used to analyze spatial patterns of AOD in the west part of Iran during the period 2003–2012. The areas affected by high daily AODs in southwest and west/northwest parts of Iran are identified using principal component analysis (PCA) and the atmospheric circulation patterns for these high AODs are classified in six clusters for each region, with larger frequencies in spring and summer. Despite their between differences, the weather clusters are mostly associated with a strong westerly/northwesterly flow (Shamal wind) across the Iraqi plains and southwest Iran from May to September, which is triggered by the pressure gradient between the North Africa/Mediterranean high and the monsoon low over southeast Iran. In the cold season, the pressure gradient between the Kurdi cut-off low and the high pressure over North Africa facilitates frontal dust storms that enhance the dust AOD over the west parts of Iran. The Caspian Sea high-pressure system during summer intensifies the easterly-northeasterly winds from the Karakum Desert to northwest Iran, while in winter, the strengthening of the Siberian High and its expansion over the Caspian Sea trigger strong cold northerlies over central/northwest Iran. In addition, the convergence of south/southwesterly winds, as a result of the surface low-pressure in the southern Arabian Peninsula, facilitates pre-frontal dust storms toward southwestern Iran, mostly during March–April. In summer, the gradient zone between the Iraq low-pressure and the Zagros high-pressure enables transport of dust aerosols toward west-northwest Iran. Identification of the weather clusters associated with intense dust storms over the west part of Iran is critical for the prevention of the deleterious effects of dust on climate, ecosystems and human health. • Determination of weather clusters in the Middle East associated with high AODs in the west part of Iran • AOD hotpot areas are attributed to convergence of winds over Iraq and southeast Iran • Most clusters are associated with cyclonic conditions over Iraq and frontal dust storm • Shamal dust storms carry large amounts of dust over west Iran • Kurdi cyclone/cut-off low plays a major role in dust-storm dynamics [ABSTRACT FROM AUTHOR]