Dust and clouds dance over the Sahara
More dust blows out of the Sahara Desert and into the atmosphere than from any other desert in the world, and more than half of the dust deposited in the ocean lifts off from these arid North African lands. Saharan dust influences the fertility of Atlantic waters and soils in the Americas. It blocks or reflects sunlight and affects the formation of clouds. By way of the dry Saharan air layer, dust either promotes or suppresses the development of Atlantic hurricanes, an enigma that scientists are trying to sort out.
In early September 2014, it looked like this sandy landscape had changed places with the sky. This photograph was taken by astronaut Alex Gerst on 8 September 2014, from the International Space Station. The ISS was over Libya at the time, and Gerst was looking south-southwest over a storm that stretched hundreds of kilometres across the sand seas of the Sahara.
In the photo, winds appear to be coming out of the east or northeast (left), and the sun is setting to the west (right in this image). Billowing cumulus and cumulonimbus clouds suggest that a cold, windy front was moving across the desert, perhaps a haboob. The African land surface was almost completely blocked from view by the thick dust; even the lower portions of some clouds were obscured.
"It's a spectacular image," said Leo Donner, an atmospheric physicist at NOAA's Geophysical Fluid Dynamics Laboratory. "What appear to be convective anvils are protruding above a dusty layer, and I'd speculate that the narrower convection cells on which these anvils are resting are obscured by the thick dust. The four small cylinders with tops that look like chess figures [upper right] have structures very much like the idealised plumes we use for cumulus convection in climate models."
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Credit: NASA Earth Observatory