Flight STS-7; 18.5N, 111.5E, 23 June 1983
Internal waves forced by the tides are common sights to the astronauts, especially along coasts where a shallow shelf extends several miles seaward from the shore. Four sets of such waves were observed by the Challenger's crew as they orbited over Hainan Island and the South China Sea. The waves, each representing a high tide of the diurnal tidal cycle, had crossed the shelf off Hainan, and the peaks of the waves were intersecting the sea surface. This excellent view provided the opportunity for the crew to photograph internal wave packets that had been produced over two days by the tidal action in the South China Sea, a scene seldom observed before.
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