Abstract
The Sistan Basin has been recognized as one of the most active dust sources and windiest desert environments in the world. Although the dust activity in Sistan maximizes during the summer, rare but intense dust storms may also occur in the winter. This study aims to elucidate the atmospheric dynamics related to dust emission and transport, dust-plume characteristics, and impacts on aerosol properties and air quality during an intense dust storm over Sistan in February 2019. The dust storm was initiated by strong northerly winds (~20 ms−1) associated with the intrusion of a cold front from high latitudes. The upper-level potential vorticity (PV)-trough evolved into a cut-off low in the mid and upper troposphere and initiated unstable weather over Afghanistan and northern Pakistan. At the surface, density currents emanating from deep convective clouds and further strengthened by downslope winds from the mountains, caused massive soil erosion. The passage of the cold front reduced the temperature by ~10 °C and increased the atmospheric pressure by ~10 hPa, while the visibility was limited to less than 200 m. The rough topography played a major role in modulating the atmospheric dynamics, wind field, dust emissions, and transport pathways. Meso-NH model simulates large amounts of columnar mass dust loading (> 20 g m−2) over Sistan, while the intense dust plume was mainly traveling below 2 km and increased the particulate matter (PM10) concentrations up to 1800 µg m−3 at Zabol. The dust storm was initially moving in an arc-shaped pathway over the Sistan Basin and then it spread away. Plumes of dust covered a large area in southwest Asia, reaching the northern Arabian Sea, and the Thar desert one to two days later, while they strongly affected the aerosol properties at Karachi, Pakistan, by increasing the aerosol optical depth (AOD > 1.2) and the coarse-mode fraction at ~0.7.
Highlights
Sand and dust storms are the result of strong, turbulent near-surface winds over arid and semi-arid areas, entraining large quantities of fine-grained soil particles into the atmosphere and transporting them thousands of kilometers downwind [1,2,3,4]
The present study focuses on examining the atmospheric circulation patterns and the dynamic processes, from local to regional scales, that facilitated an intense dust storm over the Sistan Basin on
According to SEVIRI observations, the dust storm originated from Hamoun Lake in the early-morning hours of 6 February and progressively strengthened till about noon, following a U-like pathway over the Sistan Basin
Summary
Sand and dust storms are the result of strong, turbulent near-surface winds over arid and semi-arid areas, entraining large quantities of fine-grained soil particles into the atmosphere and transporting them thousands of kilometers downwind [1,2,3,4]. Dust storms have significant impacts on the whole. Atmospheric models are increasingly available for simulations of dust characteristics, emission rates, uplift dynamics, and dust impact on radiative forcing and climate (e.g., [22,23,24]). Apart from the Sahara, the Middle East and southwest Asia emit large quantities of dust mainly in summer [30], while some rare but intense dust storms may occur during winter (e.g., [31,32]) Ground-based measurements at meteorological/atmospheric stations provide useful information about dust-aerosol characteristics via sun photometers and lidar systems (e.g., [25,26]), as well as visibility observations (e.g., [27,28,29]).
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