Noun
barchan (plural barchans)
An arc-shaped sand ridge comprising well-sorted sand.
On a seif dune the slip face develops on the side facing away from the strong wind, while the slip face of a barchan faces the direction of movement. Source: Internet
If the prevailing wind then becomes dominant for a lengthy period of time the dune will revert to its barchan form, with one exaggerated wing. Source: Internet