A plume of black smoke blowing westward is silhouetted against linear dunes in the great sand sea of northeast Libya. Smoke from flares at remote well heads is commonly seen by astronauts flying over the Sahara Desert. The plume dispersal pattern visible at the left edge of the image may be due to upper-level winds or gravitational settling of heavier particulates.
The regular pattern of linear dunes is generated by two major winds: the dominant north wind (north is towards the top right) determines the orientation of the sand dunes. Gentler easterly winds, as were blowing when this view was taken, make the dunes asymmetric, with a gentle windward (west) slope and an oversteepened downwind slope. Some oversteepened slopes even cast shadows in the early morning light. One mound of sand (top right), due north of the well head, does not fit the pattern of linear dunes. This type is known as a star dune.
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