seifn.

1925 W. J. H. King Myst. Libyan Desert xxiii. 221 In front of us..was a high three-headed sif, or longitudinal sand dune.

1931 Geogr. Jrnl. 78 16 In form it is a typical sif dune, a long straight ridge of sand with a single longitudinal chain of crests rising to billowy pyramids set at regular intervals, in silhouette something like huge saw-teeth.

1933 Geogr. Jrnl. 82 107 The Prince's map of this area shows a sudden change in the direction of the straight parallel lines of seif dunes which cross the country.

1941 R. A. Bagnold Physics of Blown Sand & Desert Dunes xv. 234 The early observers..held that it blew at right angles to the dune direction, whereas later observations over a longer period show that it blows parallel to the dunes... Both are right, since cross-winds are essential for seif formation.

1953 Sci. News 27 16 The greatest height recorded for a seif dune is 210 metres... Their lengths vary from about 60 to 120 kilometres.

1975 Nature 20 Feb. 617/2 Until the recent drought, seif dunes were mainly active in this region north of the 150-mm isohyet.

1976 Nature 26 Feb. 654/1 Nearby, near the oasis of Bilma, a small dune field of seifs and barchans again indicates that the wind at right angles to the barchans would be to the left of the main trend.