1. A sand dune that is crescent-shaped in map view. Barchan dunes form in areas of limited sand supply. They move across the desert floor with their gently sloping convex sides facing upwind and their steeply sloping concave sides facing downwind. 2. A crescent-shaped dune or drift of windblown sand or snow, the arms of which point downwind; formed by winds of almost constant direction and of moderate speeds. Also known as barchane; barkhan; crescentic dune.
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