A sandstorm (or haboob, from the Arabic for "violent wind") is a meteorological phenomenon in which strong winds lift large quantities of sand and dust particles from desert or semi-arid soil, reducing visibility below 1 km (and frequently below 100 m). The most intense ones form a wall of dust several kilometres high that advances relentlessly.
Mechanism and source regions
They occur when winds of 50-100 km/h act on dry, loose, unvegetated soils. Gust fronts from convective storms are the most spectacular trigger: cold descending air impacts the ground and spreads radially, lifting a wall of dust. They are also generated by intense pressure gradients in deserts (Sahara, Arabian, Gobi, Sonoran).
The Sahara is the world's largest source of mineral dust, emitting 60-200 million tonnes annually. This dust regularly crosses the Mediterranean, reaching Spain and Europe as haze and, when coinciding with rain, as mud rain. Intense episodes severely degrade air quality (PM10 > 200 µg/m³), affect aviation, and reduce solar photovoltaic output.
Sandstorms are increasing in frequency in some regions due to desertification, drought, and climate change. In North Africa, the Middle East, and South Asia they are a frequent cause of deaths and destruction. See also: sirocco.