Magazine article Insight on the News

Deciphering Tropical Cyclones: It's Hurricane Season, and Scientists Continue to Search for the Cold, Hard Facts about These Fearsome Storms. (Science)

Magazine article Insight on the News

Deciphering Tropical Cyclones: It's Hurricane Season, and Scientists Continue to Search for the Cold, Hard Facts about These Fearsome Storms. (Science)

Article excerpt

Microscopic ice particles can determine whether a storm unleashes hurricane-force fury or peters out meekly, say researchers who hope to turn weather forecasting into a science. The finding adds a critical piece to the most detailed picture of a hurricane ever assembled, pinpointing key factors that turn turbulence into tempest.

The number and distribution of ice particles within the tropical cyclone's imposing framework, known to exceed 65,000 feet in height, can signal its course, the investigators have found. If large numbers of small ice crystals are concentrated toward the hurricane's top, they will reflect more sunlight, cooling the storm's upper levels while its bottom remains relatively warm. This contrast of air temperatures between extremities might contribute to the storm's strength, just as a cold front moving into warm, moist air triggers thunderstorms.

"It turns out the temperature in the upper levels of the 'eye' of the hurricane is most critical to how low the surface pressure gets; the lower the pressure, the stronger the hurricane," says Jeff Halverson of NASA's Goddard Space Flight Center in Greenbelt, Md.

"The bottom line here is that by identifying where larger ice particles are in a hurricane, we are adding to the data we put in computer models simulating the storms, and that will improve predictions on whether a hurricane is strengthening or weakening" adds lead researcher Andrew Heymsfield of the National Center for Atmospheric Research (NCAR) in Boulder, Colo. He expects refined versions of the models to be in place within a year.

Infamous for their unpredictable, often deadly behavior, hurricanes--the name derives from the Caribbean god of evil Hurican--can bring roiling seas, roaring winds and relentless rains. By definition, a hurricane is a tropical cyclone with a warm core or eye and maximum sustained winds of at least 74 mph, occurring over the North Atlantic. The same phenomenon over the Pacific is called a typhoon.

Each year, an average of 10 tropical storms develop over the Atlantic Ocean, Caribbean Sea and Gulf of Mexico. Six of these, on average, become hurricanes. Many stay at sea, but those that touch land can wreak havoc with property and lives. On U.S. soil, hurricanes kill 50 to 100 people in an average three-year period. The deadliest of all hurricanes swept through Galveston, Texas, on Sept. 8,1900, claiming some 6,000 to 8,000 lives.

The end of last year marked the first time in 20 years in the United States that two hurricane seasons passed without a land strike. Nevertheless, the 2001 season saw an above-average 15 storms intense enough to warrant a name, nine classified as hurricanes and six as tropical storms. …

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