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Seeing the Seas' Winds

aging



J. W. Stewart
atlantic
Image: NASA/JPL

HURRICANE ALLEY in the Atlantic is clearly visible as a cluster of white vectors in this SeaWinds picture.

For nearly a year, everything worked perfectly: Beginning in June 1996, NASA's NSCAT scatterometer on board Japan's ADEOS satellite served up unprecedented details about the direction and speed of winds ruffling even the most remote corners of the earth's oceans. Using this feedback, meteorologists were better able to track the weather, predict storms and advise mariners. But in June 1997, ADEOS blinked adios--and the data stream went dead.

Now, however, a new scatterometer-satellite duo has filled the void. Two weeks ago the Jet Propulsion Laboratory publicly issued the first calibrated measurements from NASA's SeaWinds device on the orbiter QuikSCAT--nearly eight months after its launch atop an Air Force Titan II. The instrument's daily data and animations are available to all on the Web.

dora
Image: LINWOOD JONES (University of Central Florida); MICHAEL FREILICH (Oregon State University)

DORA packed winds reaching 90 miles an hour at its core, according to SeaWinds data.

"We're opening the tap on this global data to the world," said Michael Freilich, the project's principal investigator and professor at Oregon State University, Corvallis. "SeaWinds's measurements of the direction and strength of the winds at the ocean surface give us new knowledge that, in combination with satellite measurements of clouds, temperature and other data, can be used for understanding how different weather systems and storms develop, and for predicting weather over the entire globe."

The SeaWinds scatterometer works, like its predecessor NSCAT, by taking advantage of the cat's paws--or tiny capillary waves--that wind creates on the ocean surface. A rotating dish antenna on the device emits microwave pulses at a frequency of 13.4 gigahertz. These waves penetrate the earth's cloud cover, hit the cat's paws and backscatter, generating a telltale interference pattern. QuikSCAT orbits some 800 kilometers up in such a way that SeaWinds scans 90 percent of the earth's skin within a single day.

Given such broad reach, SeaWinds readily spied Hurricane Dora in the eastern tropical Pacific Ocean on August 10, 1999. It recorded a surface wind speed at the cyclone's core of nearly 40 meters per second (90 miles per hour). So, too, it captured the early August rampage of Typhoon Olga, tracking the storm from a mere depression east of the Philippines to torrential rains and 50-knot winds (57 miles per hour) over North and South Korea. And surely SeaWinds will continue to detect other budding weather systems, as well as polar ice migrations and climate shifts, in the near future--at least until its next incarnation lifts off on board ADEOS-II sometime this year.

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