16 August 2010

Hurricane formation linked to sea colour

Agence France-Presse
A change in the colour of the ocean could dramatically impact the number and intensity of hurricanes, according to a recent U.S. study.
Tropical Cyclone Fay

Tropical Cyclone Fay over Western Australia. Ocean colour has been linked to hurricane intensity, according to recent studies. Credit: NASA

WASHINGTON: A change in the colour of the ocean could dramatically impact the number and intensity of hurricanes, according to a recent U.S. study.

A team of researchers with National Oceanic and Atmospheric Administration (NOAA) ran computer simulations of such a change in the North Pacific, a region that accounts for more than half the world’s hurricane-force winds.

The main factor is the green tint ocean water takes when there are large concentrations of chlorophyll, a pigment that helps tiny organisms known as phytoplankton convert sunlight into food for the rest of the marine ecosystem.

Cyclones determined by ocean colour

“We think of the oceans as blue, but the oceans aren’t really blue, they’re actually a sort of greenish color,” said lead researcher Anand Gnanadesikan.

“The fact that [the oceans] are not blue has a [direct] impact on the distribution of tropical cyclones.”

Without chlorophyll, sunlight penetrates deeper into the ocean, leaving the surface water cooler.

Cold water affects hurricanes

Cold water in turn causes changes in air circulation patterns, forcing strong winds aloft, “which tend to prevent thunderstorms from developing the necessary superstructure that allows them to grow into hurricanes,” the researchers said.

Phytoplankton populations around the world have been declining over the last century, they said, citing recently published research.

The study is to appear in an upcoming issue of Geophysical Research Letters.

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