Thursday, March 5, 2009

Lunar Cycle Turns Hurricanes Into Beasts

Michael Reilly, Discovery News

Werewolves aren't the only terrors that follow the lunar cycle; hurricanes strengthen more often under a new moon than at any other time, according to a new study.

The moon's spooky influence on Earth and its denizens is legendary, and rightly so. From fertility to suicide, most phenomena attributed to Luna are almost exclusively superstition.

But Peter Yaukey (BIO-PDF) of the University of New Orleans has found what he thinks is real evidence that the phases of moon drive hurricane behavior. Storms that occurred in the Atlantic Ocean between 1950 and 2007 were more likely to form right after the new moon. They also intensified 49 percent more often after a new moon than at any other time in the 29.5-day lunar cycle.

Over the last century, Yaukey said, a smattering of scientific research has hinted that the moon may influence rain patterns, thunderstorms and other meteorological events. Explanations for why this is are many, but nothing conclusive has been shown.

"I had a lot of skepticism attributed to the moon, and I still do in a sense," he said. "It's not enough to have a pattern in the data. You need to have a mechanism to explain it."

There are a range of possibilities. Just as the moon pulls on Earth's oceans and creates the tides, it also tugs on the air above it. Lunar atmospheric tides are thought to be weak, but could create favorable conditions for storms to strengthen.

The moon's gravity may also pull cosmic dust into Earth's atmosphere in a cyclical fashion, perhaps seeding cloud formation and precipitation.

The most promising explanation is internal tides encouraged by the lunar cycle. The currents beneath the ocean surface could circulate warm water up underneath a storm, supplying it with the energy it needs to intensify.

But before scientists seek explanations for the connection they must make sure it's real, said Gabriel Vecchi of the National Oceanic and Atmospheric Association in Princeton, N.J.

"There's an easy way to do an independent test for this," he said. "Go back and look back at Atlantic hurricane data from 1878-1950 to see if there's still this pattern."

Only 13 percent of the world's hurricanes occur in the Atlantic Ocean. So if the moon is really influencing hurricanes, the signal should show up in Pacific and Indian Ocean storms, too.

If the pattern persists through those tests -- and if the data aren't biased by any human tendency to perform scientific measurements on a monthly cycle -- then Yaukey may be onto something.

"Those are two big 'ifs'," Vecchi said. "But if you get past those, then the subsurface ocean is where I'd look first -- internal tides do a lot of mixing."

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