Dust-storm dynamics over Sistan region, Iran: Seasonality, transport characteristics and affected areas

The present work examines the seasonality, dust-plume altitudinal variation and affected areas for dust storms originated from the Sistan region, southeastern Iran during the summer (June–September) months of the period 2001–2012 synthesizing local meteorological records, satellite observations (TOMS, OMI, METEOSAT, MODIS) and HYSPLIT forward trajectories. Dust-storm days (356 in total) are associated with visibility below 1 km at Zabol, Iran meteorological station with higher frequency and intensity in June and July. Monthly-mean composite maps of TOMS and OMI AI show high (>3–3.5) values over Sistan and nearby downwind areas. HYSPLIT forward-trajectory analysis at 500 m for air masses originated from Sistan on the dust-storm days shows that they usually follow an anti-clockwise transport direction at elevations usually below 2 km, initially moving southwards and then shifting to east-northeast when they are approaching the Arabian Sea coast. This is the result of the influence of the local topography and formation of thermal low-pressure systems over the arid lands. It is found that in few cases the dust storms from Sistan affect central/south Arabian Sea and India, while they control the aerosol loading over northernmost Arabian Sea. The Infrared Difference Dust Index (IDDI) images, which represent brightness temperature reduction due to dust presence over land, are used at specific periods of persistent dust storms over Sistan, confirming the main pathways of the dust plumes and illustrating the importance of the region as one of the most active dust sources in southwest Asia.