National Geographic : 1977 Dec
RAAL JANL,~q NORMAL NOVEMBER: Warm surface water in the central Pacific and cool water off South America reflect usual conditions for the month. Peru Current delivers cool water into the equatorial Pacific. NOVEMBER 1976: Variations of as little as 2 0 Cin sea-surface temperatures may have intensified unusual pressure systems and the winter that followed. III winds blow inabad winter SOOPING AROUND a huge low-pressure sys tem in the North Pacific (right), and deflecting off a high-pressure ridge along North America's west coast, the earth-circling jet stream and its accompanying westerlies were diverted to Alaska in a pattern unbroken for most of the winter of 1976-77. Turning back to the south, and acceler ated by a shift of the normal Canadian low to the southeast over Newfoundland, the winds-now bearing a freight of Arctic air-funneled straight out of the northwest into the United States. And the disaster was born. Some scientists look to the oceans and their vast pools of warm and cold water (upper left) for keys to long-range prediction of such radical shifts in wind circulation. Though experts agree that sea-surface temperatures are influenced by the atmosphere, which in return is affected by the more heat-retentive water, they differ on the im portance of ocean feedback to continental weather. Changes in the Peru Current, for example, are seen by some as symptoms, not causes, of deviant weather patterns. NOVEMBER 1976: Low pressure in North Pacific and high pressure off North America's west coast strengthen a bulge in the normally circular pattern of air movement.