Dust clouds over a desert might look disorganised, but sometimes the dust particles clump together into rows. When this occurs the effect is similar to that of opening a Venetian blind, allowing more of the Sun's rays to reach the Earth.
Until now scientists were puzzled as to what caused the alignment, but new measurements show that electricity holds the key. The Cape Verde Islands, off the west coast of Africa, are frequently smothered in dust blowing off the Sahara desert. Last year atmospheric scientists Keri Nicoll and Giles Harrison, from the University of Reading, released special weather balloons into dust clouds above the islands and measured the electric charge, up to an altitude of 4km.
Their measurements, published in the journal Environmental Research Letters, showed that many of the dust particles were electrically charged, perhaps as a result of being battered by cosmic rays from outer Space, or maybe just from collisions between the particles. Theory suggests that the more the dust particles are charged, the more they could align, allowing more solar energy to pass through the gaps. Desert dust is known to have a significant influence on climate all over the world (the Sahara alone flings several hundred megatons of dust into the atmosphere every year) and this "Venetian blind" effect could play an important role, moderating the amount of solar energy that reaches Earth.