Wind Traits Over the Oceans

Two oceanographers from the College of Oceanic and Atmospheric Sciences (COAS) who are part of a special NASA Ocean Vector Winds Science Team, have each received four-year, $1.2 million grants from the agency to study ocean winds via satellite.
           
Michael Freilich, a professor and associate dean at COAS, and his colleague Dudley Chelton, who holds the title of "OSU distinguished professor," will use data from a radar scatterometer aboard the NASA QuikSCAT satellite.

The instrument measures wind speed and direction at the sea surface by scattering microwave beams from "cat's paws" waves that are generated by the wind.

"Remarkably, the scatterometer measurements are as accurate as those that can be obtained by well-calibrated buoys," Freilich said. "However, there are only about a hundred of these buoys sparsely distributed about the world's oceans, while QuikSCAT can measure winds over more than 90 percent of the global oceans each day, in all weather conditions, during day and night."

These measurements are transmitted to ground stations on earth, processed rapidly, and sent within three hours to weather forecast centers in the United States and internationally, where the wind information is used to help predict regional and global weather – and provide storm and marine hazard warnings.

But the QuikSCAT measurements don't include data within 30 kilometers, or about 19 miles, of land, Freilich pointed out, because backscatter interference from the land mass historically has contaminated the measurements. He and his research team–which includes Chelton, David Long of Brigham Young University and Clive Dorman of the Scripps Institution of Oceanography–will use the NASA grant to make adjustments to the data to account for the land interference, focusing on the west coast of the United States.

The project is particularly important, the scientists say, because the 30-kilometer zone off the coast is a critical area for wind-driven upwelling. The central coast off Oregon, for example, has been plagued by onsets of hypoxia or "dead zones" over the last few years, when warm waters and a lack of surface winds essentially starved the water of oxygen, killing off many fish, crabs and other sea creatures.

"The 30-kilometer area is where the richest upwelling occurs and it is the one where we have the least amount of accurate satellite wind data," Freilich said.

Chelton's study will focus on understanding the importance of air-sea interactions associated with sharp changes in sea-surface temperatures. Offshore water temperatures can vary greatly and areas in which cooler and warmer water meet often have unusual wind activity. The persistent nature of these small-scale wind patterns, which can occur over distances as short as 60 to 100 miles, was first documented in detail by Chelton, Freilich and other colleagues in 2004 in the journal Science, based on analyses of QuikSCAT scatterometer data.

"Wind speed increases over warm water and decreases over cool water," Chelton said. "Yet these ubiquitous wind features are not well accounted for in present computer models that form the basis for U.S. and international weather forecasts. The abrupt changes of wind speed in regions of strong temperature variations can be dangerous to mariners – especially those operating small fishing or sailing vessels.

"These features have profound implications for ocean circulation and the coupling processes between the ocean and atmosphere," he added.

Chelton will use the NASA grant to work with colleagues at the European Centre for Medium-Range Weather Forecasts in Reading, England.

The QuikSCAT satellite was launched in 1999 after a rapid two-year design and construction phase in the wake of the 1997 loss of a Japanese satellite carrying an earlier NASA scatterometer. Designed for a three-year mission, QuikSCAT still functions well after seven years.

Freilich was the original NASA principal investigator for the QuikSCAT mission. Both he and Chelton have been members of the NASA Ocean Vector Winds Science Team since its inception.

OSU's College of Oceanic and Atmospheric Sciences also collaborates with the National Oceanic and Atmospheric Administration to host the Cooperative Institute for Oceanographic Satellite Science, the first NOAA cooperative institute selected after a national competition.

The QuikSCAT scatterometer satellite measures wind speed and direction at the sea surface and provides 90 percent global coverage every day.







A QuikSCAT display of wind speed and direction around the Hawaiian Islands.







Winds cause waves and an upwelling of cold, nutrient-rich waters near the coast. However, currently there is the least information about ocean winds in a 30-kilometer zone out from the coast.