 
Satellite Data on Ocean Topography Provides Clues to Hurricane Intensity
Researchers at the Colorado Center for Astrodynamics Research at CU-Boulder have been analyzing the relationship between warm water eddies, currents and hurricane intensification using altimeter data from two Earth-orbiting satellites, NASA's TOPEX/POSEIDON and ERS-2, a project of the European Space Agency. Working with the National Oceanic and Atmospheric Administration, CCAR researchers under the direction of aerospace engineering professor George Born are assisting forecasters in predicting which storms are likely to hit coastal areas the hardest. While forecasting a hurricane's path is relatively advanced, predicting intensity and storm surge - information that could help determine evacuation areas and other safety measures - has lagged behind because of insufficient data. A hurricane is born when certain atmospheric conditions combine with sea surface temperatures exceeding 26 degrees C (79 degrees F), according to CCAR research assistant Suzanna Barth. Warm air rises off the surface of the water, creating an atmospheric low-pressure cell, which if near the equator, produces winds that bend poleward as a result of the Earth's rotation. When a hurricane is then driven by high altitude winds on a path over other warm water eddies, the additional heat may cause the storm to intensify. "Think of it as a steam engine - the more heat that's put into it, the faster it's going to run," says associate research professor Robert Leben. A CCAR analysis of altimeter data revealed that during September 1995, Hurricane Opal's winds increased from 75 miles per hour to 145 miles per hour in only nine hours after it crossed a warm eddy in the Gulf of Mexico. Hurricane Floyd, also categorized as a Category 4 hurricane before it slammed into North Carolina in September 1999, crossed several warm water columns, building up power as it moved across the Atlantic. Researchers extrapolate sea surface temperatures and the approximate thickness of warm water from daily maps of sea surface height obtained through satellite altimetry, a technique that measures the travel time of a microwave pulse reflected off the ocean's surface. An increase of 1 cm in sea level represents an increase in heat of 1 degree C for a 100-meter column of water, Barth says. Effective even when clouds block infrared signals, satellite altimetry allows scientists to map sea surface height, geostrophic velocity, significant wave height, and wind speed on all of the world's oceans in real time. The information also is vital to ship routing, fishing and fisheries management, debris tracking, and offshore industries.  Engineering Home |
At the foot of the Rocky Mountains - far from any of the world's oceans - researchers are investigating a key factor that can be used in predicting the extent of a hurricane's fury. A hurricane's passage over a warm ocean eddy or current has been linked to a marked intensification of hurricane winds.