Monday, February 4, 2019

Underwater drones could transform hurricane forecasts

Researchers found that all 11 hurricanes they investigated that went through the mid-Atlantic in summer experienced ahead-of-eye cooling. This indicator was not previously known.
The key to predicting storm intensity may lie below the surface, says Undark magazine.
In August 2011, with Hurricane Irene bearing down on the mid-Atlantic coast, Scott Glenn, an ocean engineering researcher at Rutgers University, made a bold decision.
While most other research teams moved their ships, personnel, and expensive hardware to safety ahead of the hurricane, Glenn left his data-collecting drone—a torpedo-shaped underwater “glider” about 6 feet long and worth about $150,000—directly in its path.

Because that remote-controlled glider survived Irene—much to the relief of the New Jersey Department of Environmental Protection, which technically owned it—it may have helped to change the science of hurricane-intensity prediction.
Hurricanes are considered atmospheric storms even though they can’t live without drawing fuel from warm ocean water. While scientists have long known that hurricanes leave the ocean below them substantially cooler as they pull up energy from warm water, forecast models have long assumed that ocean conditions are slow to change and therefore factor them in as constants rather than driving factors in determining a storm’s strength.
But Glenn challenged that assumption when his drone detected a rapid and sharp drop in ocean temperature ahead of Irene’s eye that coincided with a decrease in the storm’s intensity just before it hit the New Jersey shore.
He confirmed that discovery in reverse 14 months later when a rise in water temperature as Hurricane Sandy approached the same New Jersey shore coincided with an increase in the storm’s intensity.
“It’s very simple,” Glenn says. “If the ocean’s warm, it increases intensity. If the ocean’s cool, it decreases intensity. So if you want to get the intensity right, you have to get the ocean right.”
If Glenn is correct, and data like his can be made available to meteorologists and researchers in a timely way, it could dramatically improve the accuracy of hurricane intensity forecasting, which has barely budged in recent years even as track forecasting has gotten better by orders of magnitude. It could also benefit emergency agencies, particularly in cases where residents have ignored warnings because previous forecasts were overblown.
“It makes all the sense in the world,” says Jennifer Francis, a senior scientist at the Woods Hole Research Center in Massachusetts who specializes in Arctic climate change and how that affects weather patterns in the middle latitudes. Until recently, Francis worked in the same department as Glenn at Rutgers, but she conducted no joint research with him.
“This really key factor is probably going to offer a big step forward in doing a better job with intensity forecasting,” Francis said.
Until drone gliders came along, forecasters had no way of knowing what was going on below the ocean surface during a storm. Unlike the hurricane-hunter aircraft that fly into and around storms, it’s too dangerous to leave ships in their path to take measurements.
And satellites—which can only measure surface temperatures under the best of conditions—can’t detect anything through storm clouds.
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