A new way of looking into hurricanes may help forecasters predict the extent of damaging winds and waves. JPL researchers Kenneth Oslund and Philip Callahan have developed a new technique using wave height measurements from satellite altimeters to study tropical cyclones.
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|The high storm waves of a typical strong Pacific hurricane, shown on the left, cover a much larger area than those of a typical Atlantic hurricane, shown on the right. The pale blue region in the center of the two images shows the location of these high waves. Most of these are more than 4 meters (13 feet) high, twice as high as ordinary waves. |
For their study, Oslund and Callahan combined data from multiple satellite passes over many storms to create composite views, or templates, of "typical" hurricanes. To create templates for strong Atlantic and Pacific hurricanes, they averaged satellite wave height measurements from storms that occurred between 2002 and 2005. All the storms were ranked between category three to five on the Saffir-Simpson hurricane scale. The scale ranges from one for the least intense hurricanes to five for the most intense.
The results support and quantify what scientists have known for some time--that storms in the western Pacific are larger in size than their Atlantic counterparts. The Pacific storms' high waves extend out over a much larger area than those of the Atlantic hurricanes, reaching about 500 kilometers (311 miles) from the storm center, about 200 kilometers (123 miles) further than those of Atlantic storms.
"The tropical western Pacific waters are warmer than in the Atlantic tropics," explained JPL oceanographer Bill Patzert. "These very warm waters are the high octane fuel that spawn and sustain the great typhoons that batter Asia every summer and fall."
The study also shows that despite the size difference, Pacific and Atlantic storms are nearly equally powerful. The strength of the storms' winds, inferred by wave height, is similar. Waves in the center of both the Pacific and Atlantic storms reach 8 to 12 meters (26 to 39 feet) high.
Both templates show that the strongest winds, those that create the highest waves, occur in the forward right quadrant of the storms. This characteristic is a well-known feature of tropical cyclones.
"Templates like these can provide useful information to operational users of altimetry wave height data such as NOAA and the U.S. Navy," said Callahan. "Forecasters overlay near-real-time data from satellite altimeters on ocean weather maps to aid in warning of dangerous conditions at sea. Unfortunately, altimeter measurements are just a single line of data. By comparing current altimeter observations and wave model output used in forecasts to these templates, it should improve predictions of how far storm waves may extend. The templates can also be used in the development and validation of wave models that forecast where these large waves will travel."
For this project, Oslund and Callahan used measurements of significant wave height from the U.S./French TOPEX/Poseidon and Jason-1 satellites. They presented their research results at the American Geophysical Union's Ocean Sciences meeting in Portland, Ore., this winter.