Massive research effort eyes high clouds

By IRENE BROWN, UPI Science News   |   July 27, 2002 at 2:00 AM
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In the tempestuous skies over South Florida, Michael Craig and a small army of scientists are conducting intensive efforts to study clouds in greater detail than ever before in order to build better weather forecasting tools and improve understanding of long-term global climate trends.

Organized by NASA and supported by an array of U.S. government and university research programs, the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment, or CRYSTAL-FACE, involves some 450 meteorologists, physicists, chemists, engineers, technicians and pilots, as well as a small armada of exotic aircraft, with support from ground-based instruments, satellites and even the International Space Station. Craig, the project's manager, calls it "the largest earth science mission that's ever been done."

For Craig, each time he sees thick, gray cloud columns build on the horizon, he could not be happier. South Florida's frequent daily afternoon deluges may spoil everyone else's plans for the beach, but for the CRYSTAL-FACE team, the region's tropical downpours are just what the weather doctor ordered.

"Hopefully, by two or three o'clock we'll have some storms," said Craig. The team has been lucky so far, he said, able to fly three or four times a week throughout the month, depending, of course, on the weather.

CRYSTAL-FACE is an attempt to understand, once and for all, the life cycle of clouds, from their most dynamic and energetic buildups to the gentle flowing cirrus formations that speckle the skies after a storm.

Cirrus clouds, which are made of ice crystals, are the study's primary targets. Congregating between 30,000 feet and 60,000 feet in altitude, they are generated at the tops of cumulonimbus clouds, which are associated with severe wind squalls, hail, heavy precipitation and thunderstorms.

NASA's background materials on the project explain that tropical cirrus clouds, such as those overhanging South Florida, seem to play an important but complex role in Earth's climate system.

"Cirrus ice crystals scatter incoming sunlight, reducing the solar radiation reaching Earth's surface and resulting in a surface cooling effect," the text says. However, "cirrus clouds also absorb upwelling infrared radiation emitted by the surface and lower atmosphere," in other words, retaining the planet's heat when it otherwise would be reflected back into space.

Although the net effect depends on several factors -- such as cloud height and thickness and ice crystal sizes -- atmospheric scientists think the interaction between cirrus clouds and reflected radiation raises air temperatures and contributes to a warmer planetary surface.

Perhaps more important, tropical cirrus clouds affect climate through their role in Earth's "water vapor budget," NASA's backgrounder states. Though it is not mentioned nearly as often as carbon dioxide, "water vapor is the dominant greenhouse gas" in Earth's atmosphere. "The majority of the temperature change predicted in response to increasing greenhouse gas concentrations" can be traced to the water vapor feedback effect, the text explains.

Each morning, at Key West Naval Air Station, the CRYSTAL-FACE team prepares its oddball assortment of six aircraft for flights in, around, through and under the billowing clouds.

The fleet includes NASA's high-flying ER-2. A cousin of the Air Force's U-2 spy plane, the long-winged ER-2 soars so close to the edge of space its pilots must wear pressurized suits to survive.

Much of the heavy lifting is done by an ancient WB-57, whose history goes back nearly 60 years to the end of World War II. One of only two left in the world -- both now owned by NASA -- the WB-57 is capable of carrying nearly half of the 60 or so scientific instruments being used for this unprecedented meteorological study.

Also flying CRYSTAL-FACE missions is Proteus, an exotic aircraft with a slender body and odd, gracefully arcing, tandem wings. It relays telecommunications through a fat pod slung under its fuselage while its highly pressurized cabin allows the flight crew to stay aloft for up to 18 hours. More conventional is the venerable P-3 Orion, which has flown daredevil missions into the eyes of hurricanes for more than 30 years without a mishap. The workhorse UV-18A Twin Otter, which has slogged passengers and cargo to remote airfields from pole to pole, gives additional airborne support, along with a Cessna Citation II research jet.

The planes line up for takeoff to their respective posts. The ER-2 will top the skies at 65,000 feet, while Proteus will roost at 50,000 feet. They will be followed by the WB-57, the Citation and the P-3, which carries a Doppler radar station.

Bringing up the rear is the Twin Otter, carrying aerosol detectors and temperature and humidity sensors.

At times during the missions, all six planes will stack up in the sky, one on top of another, with the Twin Otter lumbering at 1,500 feet to the ER-2 at 65,000. A key objective is to fly the vertical formation over two ground weather stations, located nearby at Tamiami Airport and Everglades City, while atmospheric-scanning satellites fly overhead.

This intricate positioning allows the team to take comprehensive instrument readings throughout a chosen column of air, including size, shape, number and location of individual clouds, as well as ice crystal concentrations, temperature, humidity and pressure, all at designated altitudes.

"We try to get as close as we can to the cirrus clouds," says Dave Fahey, a researcher with the National Oceanic and Atmospheric Administration in Boulder, Colo., whose primary focus is studying nitrates in the atmosphere.

Fahey's team is interested in learning if the presence of nitric acid affects cloud formation and size. The information will be useful in interpreting data from a new Earth-monitoring satellite called Aura, which NASA is preparing for launch.

"There's quite a synergism here," says Fahey, looking over the line of aircraft ready for takeoff. "These aircraft and the instruments really complement each other so that we're able to do things, look at things as a set. It's the ultimate real-time experiment."

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