What's a Cyclone?

ByNed Potter

March 20, 2006 -- -- On the coast of Australia, the term "tropical cyclone" generates the same kind of anxiety that the word "hurricane" does along the Atlantic or Gulf coasts of the United States.

In Japan, parts of the Philippines and elsewhere in the northern Pacific, the fear-inspiring word is "typhoon."

And along the coast of India, they talk of "severe cyclonic storms."

But all these terms describe the same kind of storm -- the familiar spiral shape seen in satellite images when one approaches. The storm that hit the northeastern corner of Australia was cyclone Larry; the Australian Bureau of Meteorology maintains eight lists of common names for different years and different regions, just as the National Oceanic and Atmospheric Administration does for storms that affect the United States.

The first named storm in the Atlantic this year was Alberto; the list of storms that form in the Pacific off Mexico or California began with Aletta.

In the northern Pacific off Asia, different countries contribute to the lists of names, so typhoon Kai-Tak (a Chinese name) is followed by Tembin (Japanese) and Bolaven (Laotian).

Are the storms becoming worse by the planet's warming climate? The issue is controversial, but two scientific papers published last year suggest the answer is yes. (Scientists generally refer to hurricanes, typhoons and the like as tropical cyclones.) The number of storms has not risen, said researchers, but their severity generally has. Cyclone Larry, with maximum winds of 180 mph, was described as the strongest to hit the Australian coast since 1974.

Adding to the complexity of measuring trends in storm strength is the back-and-forth pattern of El NiÑo and La NiÑa along the equator in the Pacific. An El NiÑo is a giant patch of unusually warm water; a La NiÑa is the opposite. A La NiÑa has formed in the last few months; it generally means dry weather for the southern United States -- and severe rain for northern Australia.

The terms "hurricane," "typhoon" and "cyclone" come from different cultures but have now been standardized so that they take effect at the same point -- when a storm has sustained winds of 75 mph (117 kilometers an hour, or 64 knots).

The World Meteorological Organization categorizes and keeps track of storm names, and when a storm becomes sufficiently serious, the affected country can apply to have its nickname removed from the list. Most of these decisions are simple: There will never be another Hurricane Katrina.

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