Scientists Use Balloon to Study Storms

AFTER the go-ahead from the Juan Santamaría International Airport control tower, researchers released a helium-filled weather balloon strapped onto a boxy, Styrofoam payload and shook hands while it buried itself in the clouds on its 30-kilometer ascent. The launch Wednesday concluded 25 daily launches in the Ticosonde project, collecting atmospheric information using equipment that has never before seen the skies above Central America. It is part of a larger atmospheric study and satellite test funded by the U.S. National Aeronautics and Space Administration (NASA) (TT, July 1).The balloon yanks a bundle of sensors behind it into the stratosphere – the layer of atmosphere from 17-50 km above sea level – until the balloon, expanding as air pressure around it drops, bursts and drops its goods. The equipment is attached to a parachute and, if it falls on land, can survive the impact and be reused. The problem is finding them afterward.A notice is taped to each informing their finders that the contents are not hazardous and they will be rewarded $20 for their return. Of the 25 released, as of Wednesday, eight had found their way back to the base at the airport in Alajuela, west of San José. It’s a $2,000 package, including the balloon and the helium that fills it, and researchers said most fell into the ocean.THE cargo consists of four or five Styrofoam boxes, together about the size and shape of a 20-inch TV, bound with orange packing tape and shot through one awkward extension with a 1-foot hollow steel rod. As it hums, wires jut from between box lids, and in one of its compartments, cryogen – famed for its use in preserving the human body – sloshes around helping it detect humidity levels.A crew of scientists from United States and Costa Rican institutions is collaborating on the project to discover some of the atmospheric processes that prop up tropical storms and underlie weather patterns here. Professors and students from Costa Rica’s two largest universities, the University of Costa Rica and the Universidad Nacional, work with weather researchers and a project overseer from the University of Colorado (CU), using NASA funds.The launches have supplemented the daily radiosondes that the National Meteorology Institute (IMN) has piggybacked on hydrogen-filled weather balloons for more than 25 years.THE difference, explained CU atmospheric research scientist Holger Vömel, is accuracy and the number of readings these bundles can take. The radiosonde is the typical atmospheric test instrument, launched daily or twice daily from 2-3,000 stations worldwide, and, together with their balloons, are frequently scapegoats for UFO sightings. It is a package slightly larger than a deck of cards that radios measurements of wind speed, temperature, humidity and air pressure as it rises. When its balloon bursts, it falls and is destroyed.The Ticosonde package takes all the radiosonde measurements – in fact, it has a radiosonde on it – duplicates, even triplicates some of them, and measures ozone levels.Ozone levels reveal how the air is mixing. The ozone collects at higher altitudes above Costa Rica now, Vömel said, because the air is in constant movement during the rainy season. Hot air constantly rises and displaces cooler air, a process called convection, creating clouds and rain this time of year. He expects the ozone to collect at lower levels in the dry season when the air is not so frenetic.THE Ticosonde also duplicates the measurements of the U.S. scientific satellite Aura when the satellite passes above the balloon, allowing scientists to verify that its instruments are working well.The cryogen, a liquid that boils at -160° Celsius (-256° Fahrenheit), freezes the water vapor in the air to calculate humidity. It is more accurate than the radiosonde, especially at high altitudes where the air is much drier and colder.“This is the only technique that measures the whole range, from the surface to 30 km,” Vömel said.The bundle of sensors drops steadily on a clicking winch as the balloon ascends. It will eventually hang about 30 meters below the balloon as it does its work to avoid water vapor clinging to the balloon.“Water vapor sticks to everything, and the air gets contaminated around the balloon,” Vömel said.THE Ticosonde takes three different humidity measurements, including the radiosonde’s, which helps scientists crosscheck the accuracy of the readings, especially that of the radiosonde.“With 2-3,000 of these (radiosondes) going up every day, it is important to know how accurate they are,” Vömel said.IMN Meteorologist Werner Stolz saw off the last daily hydrogen balloon from the doorway of the institute’s base at the airport. The base is a computer room attached to a glorified shed where huge cisterns produce hydrogen. Hydrogen, though much more volatile than helium, is cheaper to use. Fortunately, Stolz said, there have been no explosions to date.Launches of the Ticosonde bundle will continue, but on a reduced schedule – once a week and later once a month.