World’s windiest ocean locale

News briefs from the American Meteorological Society annual meeting being held January 11 – 15 in Phoenix

Thar she blows: A weather report from the world’s windiest ocean locale

WINDY REGION Shown are satellite-derived average wind speeds for east-moving storm systems spilling past Greenland during the winter months from 1999 through 2004. Red denotes wind speeds above 20 meters per second; cooler colors represent slower winds. IMAGE CREDIT: Renfrew

A buoy anchored southeast of Greenland dutifully gathered wave and weather data in one of the world’s most hostile environments for more than five months,  until the really rough weather of winter arrived and the buoy snapped free — but not before it confirmed satellite data suggesting the region is the world’s windiest for oceans.

The seas east of Greenland’s southern tip, a desolate point called Cape Farewell, are notoriously storm-tossed, says Ian Renfrew, an atmospheric scientist at the University of East Anglia in Norwich, England. As storm systems race eastward from northernmost Canada, their frigid winds either pass over Greenland’s kilometers-thick ice sheet and gain speed as they rush down its eastern slope, or they spill around the southern tip of the island. Waters in the area are likewise buffeted by storm systems that approach the island from the east and are then steered southward by Greenland’s icy blockade.

The region’s bad weather is what spurred Renfrew and his colleagues to tether a weather buoy to the 3-kilometer–deep seafloor there in the summer of 2004. At least 10 times that summer and fall, and sometimes for extended intervals, instruments on the floating platform measured winds exceeding speeds of 20 meters per second (about 45 miles per hour), the researchers reported January 13 at the annual meeting of the American Meteorological Society in Phoenix. Then on December 7, after less than six months in service, either high winds or huge waves — or both — pummeled the buoy and broke its tether.

Satellite-based sensors supplied data in recent years indicating that the ocean region east of Cape Farewell is the windiest in the world, says Renfrew. Furthermore, he notes, the buoy’s measurements suggest that the wind speeds inferred from the satellite data are accurate — a calibration that’s useful for analyzing similar data gathered for other parts of the ocean.

Renfrew and his colleagues estimate that 20 percent of the time winds at the site east of Cape Farewell blow even faster than 20 meters per second.

Rain machines: Tropical cyclones supply bulk of rain for some places

Tropical cyclones, the immense rotating storm systems that include hurricanes and their weaker cousins, typically last only a short time and cover a relatively small part of Earth’s surface. Nevertheless, at some latitudes these storms provide a substantial part of the region’s rainfall, a new study suggests.

For each year from 1998 through 2007, meteorologists tallied between 90 and 100 tropical cyclones that had peak wind speeds of at least 17.5 meters per second (about 39 miles per hour), says Christopher L. Williams, a recent graduate of Georgia Tech in Atlanta. Using satellite data, he and colleague Frank Marks Jr. of NOAA’s Hurricane Research Division in Miami estimated total worldwide rainfall for those years, as well as the amount of precipitation dumped only by the tropical cyclones.

Overall, tropical cyclones drop between 2 and 3 percent of the world’s rainfall, the researchers reported January 13 at the annual meeting of the American Meteorological Society in Phoenix. And that fraction is particularly small at latitudes near the equator, where rainfall is plentiful but the forces that drive large-scale atmospheric rotation and cause cyclones to develop are practically nonexistent, says Williams. However, at latitudes between 15° and 30° — a swath that in the Northern Hemisphere stretches from central Honduras to just north of New Orleans — rainfall is less abundant, and tropical cyclones account for as much as 17 percent of annual rainfall.

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