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Scientists Scan Mud For Hurricane Patterns Newest Technologies Improve Prediction
Scientists Scan Mud For Hurricane Patterns
Peter N. Spotts Staff writer of The Christian Science Monitor
November 6, 2003
WOODS HOLE, MASS. -- To find out what makes a hurricane tick, you have to fly through it. To find out how often hurricanes strike land, you need to dig for them.
As more condos, office towers, and housing tracts spring up in cities along America's East and Gulf coasts, researchers are scanning mud they bring up from coastal marshes and ponds for clues about the history of major hurricanes.
The approach is relatively new, scientists say. With it, they hope to give residents, emergency planners, building and zoning boards, and insurers a better handle on the risk densely populated areas face from these storms. When combined with other emerging techniques, these "paleo-tempestologists" add, information they glean might help determine whether global warming could generate more- frequent or more-intense storms.
"The motivation is to extend the historical record" for major hurricanes, says Richard Murnane, who heads the Risk Prediction Initiative at the Bermuda Biological Station for Research.
The insurance industry is interested in the most intense storms, he says, but these are rare. Only three Category 5 storms - the most destructive - have hit the US in the past century. The latest was Hurricane Andrew, which struck Florida and Louisiana in 1992, killing 23 people and causing $26.5 billion in damage.
The potential of mud coring became apparent in 1993, when Kam- biu Liu and Miriam Fearn at Louisiana State University showed that paleo-hurricanes left their mark as sand layers in mud cores taken from the bottom of coastal lakes along the Gulf. But could the technique work for hurricanes along the East Coast?
"Initially, I was somewhat dubious," says Jeff Donnelly, a geologist at the Woods Hole Oceanographic Institution. He had spotted sand layers in mud cores he pulled from coastal marshes to study effects of changing sea levels on ancient ecosystems. The marshes sat behind barrier beaches, which can be overswept by tidal surges during storms. The surges drive sand into the marshes. But when powerful nor'easters clobber the East Coast they can generate surges of their own. Telling the two apart might be tough.
Despite his misgivings, Donnelly and his colleagues picked sites where winds from nor'easters came from the wrong direction to add sand to marshes. They punched cores from the marshes, dated the organic material, then compared the results with the historical record. "The only thing these sites were recording in the historic interval was hurricanes," he says. "I was amazed at how well it came out."
Dr. Donnelly published the results of his first hurricane- related study, based on cores pulled on Succotash Marsh in Rhode Island in 2001. He's also looking at sites along the Connecticut and New Jersey coasts and in wetlands near New York City. There, a hurricane in 1821 sent a 10- to 13-foot storm surge over Manhattan.
Yet as successful as coring has been, it can only yield dates of events to within a decade or two. When historical records aren't available as a back-up, a sand layer could appear to be a hurricane but actually mask several storms.
Woods Hole geochemist Anne Cohen is looking at corals to solve the problem. Coral layers can be dated within months and their chemical composition reflects that of the water. Rainfall from hurricanes carries a chemical signature. So by examining coral growth-bands, researchers can pin down dates for hurricanes during the broader periods that coring unveils. In 2000, Dr. Cohen tested the technique in the Virgin Islands and found records of several hurricanes written in coral. Cohen and Donnelly hope to study cores and coral samples from Puerto Rico next year.
"We really want to know how hurricane frequency and intensity will change with global warming," Cohen says. "Right now, the scientific community is divided."
Newest Technologies Improve Prediction
Scientists: Isabel is being closely studied as part of the continuing drive for better forecasts
By Frank D. Roylance | Sun Staff
September 18, 2003
For decades Americans have flocked to the cities and beaches of the Atlantic and Gulf coasts, setting up homes, resorts and businesses like pins in a bowling alley.
Hurricanes such as Isabel are the bowling balls, and scientists such as Jeffrey B. Halverson spend their lives trying to understand them so forecasters can better predict where each will strike.
With millions of lives and billions of dollars in property at stake, plus an unprecedented set of tools at scientists' displosal, Halverson says, Isabel "is probably going to be one of the best-studied storms in history."
But even with the best satellites, airborne equipment and computer models, scientists still confront many mysteries. "It behooves us to better understand how these storms operate ... so we can get people out of harm's way," Halverson says.
Halverson is a research meteorologist at the Joint Center for Earth Systems Technology, operated by the University of Maryland Baltimore County and the NASA Goddard Space Flight Center.
He is part of a small army of experts who have labored for decades to improve hurricane science, armed with a constellation of satellites, a fleet of airplanes, batteries of radar installations and squads of ground troops with fixed and mobile technology.
Without a word of apology, they are following Isabel's every move, measuring her temperature, air pressure and rainfall, her winds and storm surges.
Their work began weeks ago as Isabel appeared in the eastern Atlantic Ocean, and it intensified as she gathered her skirts into an almost perfectly symmetrical - and fearsome - Category 5 hurricane.
It hasn't always been this way.
For centuries, these storms crashed ashore with little, if any warning, and at a terrible cost.
The Great Galveston Hurricane of 1900 was supposed to strike no more than a glancing blow. Instead, its 140-mph winds and 16-foot storm surge demolished a third of the island city of 30,000, killing as many as 12,000.
The Category 5 Labor Day Hurricane of 1935 surprised residents and workers in the Florida Keys with 200-mph winds and a 25-foot storm surge. More than 200 people were killed, and 164 others were never found.
With intense development along America's coasts today, forecast accuracy is even more critical. A missed forecast can invite catastrophe. An unnecessary evacuation erodes confidence in hurricane warnings - and costs a fortune.
"Every mile [of coastline] evacuated costs $600,000 in lost economic activity per day," Halverson says.
For decades, forecasters depended on reports from remote stations and ships at sea. They got new eyes in the 1960s, when the first weather satellites gave them a high perch. But even the best of those could do little more that look down at the storm clouds and track their movement. "It's like if you put your hand on the hood of a car. You can feel how fast it's running, and how hot it is. But you couldn't look inside," Halverson says.
The latest satellites, however, use microwave technology to "see" through 10 miles of storm clouds and record images of rainfall and sea-surface patterns.
One of them, the Tropical Rainfall Measurement Mission (TRMM), was launched in 1997 by NASA and the Japanese space agency. It transmits a microwave beam that scatters when it hits raindrops. Like TV weather radar, the reflected pattern details the hurricane's rain bands, how fast they're moving and in what direction.
"It allows you to better understand how well the storm is organized," Halverson says. "If they're nice and concentric and tightly packed, it probably tells you it's a fairly intense storm."
TRMM also enables forecasters to say where the most intense rain is falling.
Another microwave satellite, NASA's 3-year-old Quick Scatterometer (QuickSCAT), provides detailed information on the "roughness" of the ocean's surface.
"If it's rough, there's probably a lot of waves, and wind speed is probably pretty strong," Halverson says. "It's a good indication of the direction and strength of winds just above the ocean's surface."
That, in turn, helps determine how fast winds are blowing around the eye of the storm.
But satellites have their limitations. TRMM and QuickSCAT can provide images of a hurricane only twice a day. And the smallest features they can capture are 4 kilometers square.
"It's like having a grainy picture," Halverson says.
So the "gold standard" in hurricane science since the 1940s has been the airplane. As soon as hurricanes move west of Puerto Rico, a small squadron begins flying regular missions through the storm, sometimes skimming jus a few hundred feet above the waves.
To provide basic information, Air Force "Hurricane Hunters" from Keesler Air Force Base in Mississippi crisscross the storms, dropping 20 or 30 instrument packages into the clouds.
Called "dropsondes," the foot-long cylinders parachute down, transmitting temperature, wind speed and barometric pressure until they hit the sea. The information is relayed by satellite to hurricane forecasters in Florida and incorporated into the complex computer models they use to craft predictions.
Meanwhile, the National Oceanic and Atmospheric Administration flies three Orion P-3 submarine hunters with more sophisticated instruments that provide enhanced data scientists need to understand the storms' development.
Finally, a NOAA Gulfstream executive jet flies around the storms at 45,000 feet, gathering information on the weather conditions that steer the hurricane's movement.
Far above the storm, NOAA's GOES 11 and 12 satellites hover in geosynchronous orbits over the eastern and western United States. They provide minute-to-minute coverage of any changes in a hurricane's structure, water content and temperature.
All this technology has enabled forecasters to improve their storm track forecasts by 30 percent, extend their predictions to five days from three, and reduce evacuations - saving millions of dollars.
More tools are being enlisted. For Isabel, researchers from Texas Tech University were rolling 30-foot instrument towers and mobile radar stations onto the Outer Banks yesterday. The National Severe Storms Laboratory and the National Center for Atmospheric Research have also put "Doppler on Wheels" radar in the storm's path.
The mobile doppler units "have revolutionized the study of tornadoes and other violent and small-scale atmospheric phenomena," says NCAR scientist Josh Wurman.
But scientists still face many mysteries. For example, how do hurricanes change intensity? Isabel spun up to Category 5, with top winds roaring at 160 mph. It stayed strong for days, then faded without warning to Category 2, with 105-mph winds.
Scientists also don't know why some hurricanes produce torrents of rain -10 or 15 inches - while others don't.
An answer might save lives because inland flooding is responsible for 63 percent of hurricane fatalities. "There doesn't seem to be a good correlation between the intensity of the storm and the amount of rain it produces," Halverson says.
No one is giving up on those mysteries. NASA wants to launch eight to 10 microwave satellites like TRMM, enough to measure rainfall every three hours instead of twice a day. And NOAA is considering a fleet of pilotless aircraft to expand the coverage provided by Hurricane Hunters.
With Isabel howling ashore amid an unprecedented array of instruments, Halverson says, "It's an exciting time if you're a hurricane researcher - but maybe not so exciting if you live in the path of this thing."
The Associated Press contributed to this article.