On September 30, 1974, a katabatic wind (williwaw) swept seaward across the Copper River delta for 72 hours at velocities up to 39 m/sec. Sediment entrained in the basal 200 meters of the atmosphere seaward of the beach revealed a structured flow, consisting of large streaks 30 to 50 m in diameter, separated by clear lanes of approximately equal width. The driving mechanism may be the large-scale helical flow patterns that have been described in the atmospheric and oceanic boundary layers. The large streaks are of the same scale as desert sand strips, or continental shelf sand ribbons.

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