Borne on a balloon

Years before it housed aircraft or supercomputers, NCAR was sending balloons into the stratosphere. Bolstered by new space-age technology, this simple but powerful observing strategy gathered critical data from hard-to-reach places.

Balloons had been launched for scientific purposes since the 1800s, but the original plans for NCAR did not include a balloon facility. That changed after a 1960 conference—one of NCAR’s first—when experts convinced Walter Orr Roberts that ballooning had a rightful place at the new center. Within months, Roberts had brought expert Vincent Lally on board to head up the project. By 1963 the National Scientific Ballooning Facility (NSBF) was in place near Palestine, Texas, a prairie location where aircraft interference was minimal and good launch weather was frequent.

When Lally arrived at NCAR, he dreamed of combining several technologies into a balloon-based system for observing the atmosphere in three dimensions. At the time, satellites were still experimental, and the balloons carrying radiosondes (see page 15) were unable to penetrate far into the stratosphere before bursting. Lally envisioned a set of balloons floating at high altitudes for weeks or months at a time, drifting around the globe and radioing back data around the clock.

Man holding a large balloon
Robert Frykman took part in a Mesa Lab demonstration of balloons used in the GHOST program.

In order to haul heavy instruments to stratospheric heights for long periods, the new balloons would have to be huge and ultra-strong. “Modern scientific ballooning actually owes its existence to the American housewife,” Lally once observed. He noted that the increased popularity of plastic vegetable bags after World War II made polyethylene film far more affordable. When coated with Mylar, this material was highly resistant to the formation of tiny holes that could sabotage long flights. It was also highly reflective, which reduced the Sun-driven temperature changes that caused most balloons to rise by day and fall by night. Strong enough to withstand intense pressures without leaking or sinking, the resulting vehicle—a “superpressure” balloon developed largely at the Air Force Cambridge Research Laboratories—could withstand intense pressures and float at a height of constant atmospheric density without having to drop ballast at night simply to stay airborne.

As the NSBF grew busy launching instruments, including some built at NCAR, Lally and colleagues looked to other latitudes. The Soviet Union prohibited balloon overflights, so attention turned to the Southern Hemisphere, where the relative lack of land mass meant fewer radiosondes were sampling the atmosphere. NCAR teamed with New Zealand’s weather service and other partners to launch the GHOST program (Global Horizontal Sounding Technique), which kicked off in March 1966 with a launch from Christchurch. Not only did a GHOST balloon become the first to fly around the world, it completed six more circuits before falling to Earth after 51 days aloft.

“Those were exciting days, and our achievements were due in no small measure to the excellent cooperation we received from the New Zealand Meteorological Service and the volunteer balloon tracking stations around the Southern Hemisphere,” says NCAR’s Marcel Verstraete, part of the GHOST team.

Though it never became the routine monitoring system Lally and others had envisioned, GHOST was a durable success, launching more than 350 balloons over a decade’s time. One flew for 744 days at heights above 6 miles (10 kilometers). GHOST balloons provided a unique window on processes far above the southern midlatitudes and the tropics, where temperature data remain scarce to this day. High-altitude launches continue from the Palestine site, which has been managed by NASA contractors since 1987 and is now known as the Columbia Scientific Balloon Facility.

Lally kept an unpretentious attitude toward his career at NCAR, which spanned four decades. As he put it, “It’s a nice way to make a living—getting paid for blowing up balloons.”

 

Today — Radiosondes in reverse

Photo of David Parsons

"We're making accurate measurements in very hard-to-reach areas."

—David Parsons, University of Oklahoma

Each day more than 2,000 radiosondes send weather data to Earth as they ascend via balloons through the lowest few miles of the atmosphere. NCAR engineers have taken this venerable technology and, in a sense, turned it upside down. In 2006, they unveiled the “driftsonde,” based on a balloon that floats across the stratosphere over a week or more. The payload: dozens of instrument packages (dropsondes) that transmit data as they fall from the balloons’ gondola via parachute.

Photo of a driftsonde balloon in the sky
The driftsonde system includes (top to bottom) a superpressure balloon, a parachute, communications equipment, and the NCAR gondola, which holds 35 or more instrument-laden dropsondes. (Photo by Charlie Martin, NCAR.)

Vin Lally and colleagues had contemplated the notion of a driftsonde as far back as the 1970s, but they were limited by weak batteries, inadequate communication links, and heavy instruments. Technology had transcended these roadblocks by the turn of the next century. NCAR engineers and machinists worked together to produce a highly compact instrument package, about the size of a small bottle but weighing only about 140 grams (5 ounces).

Driftsondes also had to hold up to the intense sunlight and brutal cold of the stratosphere, often drifting for days in standby mode. “Try letting your car sit at minus 80 Fahrenheit for 14 days, and then try to start it,” said David Parsons, the NCAR lead on the driftsonde project and now director of the University of Oklahoma’s meteorology school.

The system proved its durability in the 2006 African Monsoon Multidisciplinary Analysis project, when it sampled incipient tropical cyclones across the eastern Atlantic. Five driftsonde units released more than 200 dropsondes, gathering data on two systems close to tropical storm strength that went on to become hurricanes Florence and Gordon.

In 2010, a set of successful launches from the Seychelles paved the way for the driftsondes’ use in late 2010 as part of Concordiasi, an ambitious project of the World Weather Research Program to reduce uncertainties about the present weather and future climate of the Antarctic. Part of THORPEX (The Observing-System Research and Predictability Experiment) and the International Polar Year, Concordiasi is led by scientists from the United States and France, the latter a world leader in ballooning technology and the primary collaborator with NCAR on the driftsonde project.

Photo of hands holding a dropsonde
An instrument laden dropsonde that transmits weather data when it is dropped via its own parachute. (Photo by Randy Redman, U.S. Air Force.)

“Retrieving all the useful information from satellite observations is a delicate process, especially over the extreme conditions found at the poles,” says Florence Rabier, head of the observations team in Météo-France’s center for numerical weather prediction. The driftsondes will gather up to 600 atmospheric profiles in and near Antarctica. These unprecedented sorties into rarely sampled regions will be used to calibrate computer models and should help scientists interpret what satellites are observing.

 

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