Dust Storms

Dust storms initiate when wind speed exceeds the saltation threshold (~5–8 m/s for dry, loose sand). Saltation — grains hopping in short arcs — bombards the surface, dislodging smaller clay/silt particles into suspension. A haboob is a wall of dust (up to 3km high) driven by the cold outflow of a collapsing thunderstorm. Saharan dust crosses the Atlantic Ocean, fertilizing the Amazon Basin with ~22 million tonnes of phosphorus annually — the desert feeds the jungle. Dust aerosols affect climate directly (scattering, absorbing sunlight) and indirectly (cloud condensation nuclei). The Dust Bowl of the 1930s displaced 2.5 million people; modern desertification makes such events increasingly frequent.