Spring Break
Oceanography professor continues research on hurricane forecasting
Tyler Will
Issue date: 9/5/08 Section: News
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Lengthy research has concluded that ocean temperatures can be used to predict a hurricane's path, and the mixing of layers of warm and cold water can be used to predict a hurricane's intensity. When combined with atmospheric conditions, an accurate forecast of a hurricane can be made.
"Over the last 15 years, the accuracy [has increased], the track error has been reduced by a factor of two," Ginis said. An error is the distance between the actual path of a hurricane and the forecasted path.
In past years, if forecasts were off by 50 miles, today they would only be off by 25 miles.
"We predict the hurricane five days in advance [today] with the same accuracy that we did for three days 15 years ago," he said.
Ginis added that while a hurricane's predicted path has been improved by 50 percent, a hurricane's predicted intensity has only improved by 25 percent.
He explained that computers have also helped hurricane forecasting, crediting commercial development for some of the success.
"Scientists, we're joking with ourselves, we're always cheering for the gaming industry," Ginis said, explaining that they push computers to have more powerful computer chips. "We take advantage of those more powerful chips."
He added that the gaming industry needs the commercial motivation because it would not be driven by science alone.
Hurricanes form when heat from warm ocean water is converted into mechanical energy in the form of wind, Ginis said. The warmer the water, the more powerful the storm.
Hurricanes strengthen over warm water and weaken over cold water. Ginis said the ideal temperature is about 80 degrees Fahrenheit, and they usually form in the tropical regions because that's where the air is warmest.
Water temperatures are factored into an equation to project the path of a hurricane, Ginis said, and the hurricane always leaves a cool-water wake in its path, because it has taken energy from the water. Ginis used the water temperatures in a model called the GFDL, and won the Environmental Hero Award in 2002.
"The questions we're asking is why the oceans are cooling, and what controls the magnitude of the cooling," Ginis said.
But the cooling, Ginis said, is difficult to track because the ocean's temperature changes all the time and different parts of the ocean cool faster than others.
Ginis attributed the spontaneous cooling to ocean currents such as the Gulf Stream and the "Loop Current," which stretches from the Yucatan Peninsula into the Gulf of Mexico and then passes the tip of Florida.
Ginis employed the Loop Current in a model called the H-WRF, which is used to forecast hurricanes.
In an effort to find out how the cooling worked, Ginis said a scientist took a propeller driven plane, which is more stable in high-wind situations, and flew at 1,500 feet above a hurricane's surface. Normally, planes fly at 10,000 feet or higher above hurricanes.
When the plane lost power to two engines, it increased elevation to prevent total power loss.
"What was interesting was that pretty much all of the engines were clogged with salt," Ginis said, explaining that hurricanes generate a large amount of sea spray, but no one had thought the spray would be found at 1,500 feet above the surface of the water.
The sea spray made scientists realize that a lot of water mixing is done when hurricanes are over the surface of the ocean, and helped solve the question what causes ocean cooling.
In the ocean, there is a warm layer and a cool layer, and the warm layer always rises to the top. When a hurricane is on the water's surface, it mixes the two layers, and the mixing can be mild to heavy, Ginis said. The heavier the mixing, the more energy is in a hurricane, but too much mixing can cause the cold layer to completely surface, causing the hurricane to weaken. Some parts of the ocean have thicker warm layers than others.
"It's like stirring sugar in coffee," Ginis said. "It can produce negative feedback. It can actually weaken it."
A limitation of the use of warm and cool layers in hurricane forecasting is inadequate technology, Ginis said.
The ocean mixing is used to help measure intensity, and water temperatures are used to help track the path of a hurricane.
The combination of ocean mixing, water temperatures, and atmospheric conditions produce the most accurate hurricane forecast, Ginis said.
