Posted: 10:06 am Saturday, August 14th, 2010

New study finds that ocean color impacts hurricane formation 

By John Nelander

Forecasters often talk about the usual suspects in tropical storm development: sea surface temperatures, air pressure and wind shear. Here’s a factor that researchers say plays a role as well – the color of the ocean water.

Surprisingly, the greenish tint that sea water takes on in the presence of large concentrations of chlorophyll can actually provide fuel for the development of tropical storms, according to the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory in Princeton, N.J.

“We think of the oceans as blue, but the oceans aren’t really blue, they’re actually a sort of greenish color,” says researcher Anand Gnanadesikan, who led the study. “The fact that [the oceans] are not blue has a [direct] impact on the distribution of tropical cyclones.”

The greenish hue is caused by chlorophyll, which is trapped within the cells of the tiny microscopic organism phytoplankton.

When there’s a lack of chlorophyll, sunlight is able to penetrate more deeply into the water, which in turn cools the surface. That cooler surface water makes hurricane generation more difficult because it makes less energy available to storm development. It also leads to drier air.

It’s worth mentioning that phytoplankton has been steadily decreasing around the world for the last 100 years. According to Wikipedia, there has been a 40 percent drop since 1950.

The study, which was focused on the North Pacific, will be published in an upcoming issue of Geophysical Research Letters, a journal of the American Geophysical Union.

* * * * *

We may not have heard the last of ex-Tropical Depression 5. The remains of this system were generating heavy rain and storms near Montgomery, Ala. today. But some computer models show ex-TD-5 moving southeast back over the warm waters of the Gulf of Mexico.

A few of them regenerate the system into a depression or storm, then move it back west toward Louisiana or Texas.

Most models are also in agreement that a system moving off the coast of Africa will develop into a tropical cyclone toward the end of next week.