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No. 97: Jan-Feb 1995

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The 627-foot water slide between australia and india

The world ocean, when viewed close-up from ship or airplane, displays the familiar microstructure of waves and currents. The view from a satellite, thousands of miles up, is startling to say the least. Huge bulges hundreds of feet high and hundreds of miles in extent appear when satellite radar altimeter data are plotted. Equally large depressions in the ocean surface also show up -- none obvious to surface observers. This unexpected macrostructure of the ocean surface is shaped by variations in the strength of the earth's gravitational field and sea-bottom terrain. Wherever the gravitational field is stronger, it creates a depression on the fluid surface. German geophysicists, in fact, have drawn a global map of the ocean's large-scale topography, as measured from the European Space Agency's ERS-1 satellite. The surface of the world ocean departs wildly from a smooth sphere. On their colored map:

"Brilliant pink and red areas are continental-size mounds of water most notable northeast of Australia, where the sea topography is up to 85 meters (280 ft.) higher than the standard ocean level. Just to the west near India, deep blue indicates a 105-meter (346-ft.) deep depression in the sea surface. Major differences in the gravity fields and terrain underlying the two regions cause a variation of 190 meters (627 ft.) in sea surface topography between these two adjoining areas."

(Covault, Craig; "ESA Radar Scans Global Ocean," Aviation Week, p. 42, October 24, 1994. Cr. J.S. Denn.)

From Science Frontiers #97, JAN-FEB 1995. 1995-2000 William R. Corliss