![]() The slowdown of the currents is predicted because increasing rain and freshwater in the North Atlantic would make the water less dense and less prone to sinking. While a sudden shutdown like in the movie won’t happen, a gradual slowing – which the recent United Nations report said was “very likely” by 2100 – could shift tropical rains south, the study suggests, as it probably has in the past. The ocean current they found to be responsible was made famous in the 2004 movie “The Day After Tomorrow,” in which the premise was that the overturning circulation shut down and New York froze over. For such a major feature there’s usually a simpler explanation,” Frierson said. “But at the same time, a lot of people didn’t really believe that explanation because it’s kind of a complicated argument. Accompanying commentary: Atmospheric science: Rainfall’s oceanic underpinningsįor many years, slanting ocean basins have been the accepted reason for the asymmetry in tropical rainfall.The reason is that as the water moves north over many decades it gradually heats up, carrying some 400 trillion (that’s four with 14 zeroes after it) watts of power across the equator. Eliminating this current flips the tropical rain bands to the south. “The question is: What makes the Northern Hemisphere warmer? And we’ve found that it’s the ocean circulation.”įrierson and his co-authors first used detailed measurements from NASA’s Clouds and Earth’s Radiant Energy System, or CERES, satellites to show that sunlight actually provides more heat to the Southern Hemisphere – and so, by atmospheric radiation alone, the Southern Hemisphere should be the soggier one.Īfter using other observations to calculate the ocean heat transport, the authors next used computer models to show the key role of the huge conveyor-belt current that sinks near Greenland, travels along the ocean bottom to Antarctica, and then rises and flows north along the surface. “It rains more in the Northern Hemisphere because it’s warmer,” said corresponding author Dargan Frierson, a UW associate professor of atmospheric sciences. In general, hotter places are wetter because hot air rises and moisture precipitates out. 20 in Nature Geoscience, explain a fundamental feature of the planet’s climate, and show that icy waters affect seasonal rains that are crucial for growing crops in such places as Africa’s Sahel region and southern India. ![]() But a new University of Washington study shows that the pattern arises from ocean currents originating from the poles, thousands of miles away. Scientists long believed that this was a quirk of the Earth’s geometry – that the ocean basins tilting diagonally while the planet spins pushed tropical rain bands north of the equator. The Palmyra Atoll, at 6 degrees north, gets 175 inches of rain a year, while an equal distance on the opposite side of the equator gets only 45 inches. A quick glance at a world precipitation map shows that most tropical rain falls in the Northern Hemisphere.
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