Shuttle’s photos show ocean’s internal waves

Press, 15 May 1985, Page 12

Shuttle’s photos show ocean’s internal waves

NZPA-NYT New York Space photography has made it evident that many areas of the world’s oceans are affected by internal waves that do not appear to any large extent on the surface. Such movements typically form on a surface separating two submerged water bodies of different density. They are of more than academic interest. Such surfaces can, for example, affect sound transmissions used to detect submarines. A dramatic series of internal waves has now been traced through the Strait of Gibraltar from photographs taken from the space shuttle Challenger last October by Dr Paul Scully-Power, an Australian oceanographer of the United States Navy, and by Navy oceanographers in aircraft “underflying” the shuttle. Seeking out internal waves was a primary goal of Dr Scully-Power’s mission. It was suspected, based on earlier observations, that they might orignate <£t the western en-

trance to the Gibraltar Strait and flow eastward into the Mediterranean. Because that sea gains less water from the rivers feeding it than it loses in evaporation, there is a net flow of water into it through the strait from the Atlantic, modulated by semidiurnal tides. Bottom water is diverted upward as it meets the shallow sill at the western entrance to the strait, forming a standing wave across the stretch between Spain and Morocco. , This produces an intense “boil” on the water surface. According to the Naval Ocean research and Development Activity in Mississippi, a narrow zone over the standing wave remains smooth, although the flow of water there appears swift enough to affect the heading of ships. It has previously been suspected that eastward moving internal waves might originate at the sill but according to the Navy “there was no proof.”