WASHINGTON — A change in the color of ocean waters could have a drastic effect on the prevalence of hurricanes, new research indicates. In a simulation of such a change in one region of the North Pacific, the study finds that hurricane formation decreases by 70 percent. That would be a big drop for a region that accounts for more than half the world’s reported hurricane-force winds.
“We think of the oceans as blue, but the oceans aren’t really blue, they’re actually a sort of greenish color,” said Anand Gnanadesikan, a researcher with the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey. “The fact that [the oceans] are not blue has a [direct] impacton the distribution of tropical cyclones.”
About the image: In the oceans, shades of blue indicate lower chlorophyll concentrations. Image credit: NASA
Gnanadesikan compared hurricane formation rates in a computer model under two scenarios. For the first, he modeled real conditions using chlorophyll concentrations in the North Pacific observed by satellites. He then compared that to a scenario where the chlorophyll concentration in parts ofthe North Pacific Subtropical Gyre — a large, clockwise-circulation pattern encompassing most of the North Pacific — was set to zero.
In the latter scenario, the absence of chlorophyll in the subtropical gyre affected hurricane formation by modifying air circulation and heat distribution patterns both within and beyond the gyre. In fact, along the equator, those new patterns outside the gyre led to an increase in hurricane formation of about 20 percent. Yet, this rise was more than made up for by the 70 percent decrease in storms further north, over and near the gyre. The model showed that more hurricanes would hit the Philippines and Vietnam, but fewer would make landfall in South China and Japan.
A decrease in hurricanes in the North Pacific is just one example of how changing chlorophyll concentrations can have far-reaching, previously unconsidered, effects. The specific outcomes over different patches of the ocean will vary based on local currents and ocean conditions, said Gnanadesikan.
*Source: American Geophysical Union (AGU)