THE engines generating global moisture and airflow patterns – the tropics and the sky above them – have divulged some of their secrets to international teams of balloon-launching and converted-U.S.-spy-plane-flying scientists in Costa Rica over the last four years. Now, rounding out the latest in a series of information-collecting projects that began with the 2001 construction of the seashell-like tent hangar in Juan Santamaría International Airport in Alajuela, northwest of San José, researchers are prepping for a monumental worldwide tropical study in January. The new study, focused on Costa Rica, will encompass data-gathering stations in San José, Indonesia, Hawaii, Micronesia and the Galapagos Islands.Scientists from the U.S. National Aeronautics and Space Administration (NASA), universities and private organizations teamed with Costa Rican scientists from the two largest national universities, the National Meteorological Institute (IMN) and the National High Technology Center (CENAT) – founded by U.S.-Costa Rican astronaut Franklin Chang – to gather atmospheric measurements and apply them to a handful of projects under way in both countries.Last week, in a series of presentations at the Universidad Nacional in Heredia, northwest of San José, representatives of those projects unveiled their results and goals for further research with Ticosonde, the folksy Costa Rican moniker bestowed on extensive, periodic weather balloon launches that began last year.The aim of their efforts is the calibration of cutting-edge atmospheric measurement instruments and a deeper understanding of the processes that govern worldwide weather patterns.FROM June to September 2004 and again from June to August this year, researchers launched four balloons daily, each laden with an arsenal of sensors to calculate the humidity, temperature, wind speed and ozone content of the atmosphere and how they change as the balloon ascended up to 30 kilometers above Costa Rica. Twenty-four helium-filled balloons shuttled the special cargo of a cryogenic frost-point hygrometer – a humming bundle of Styrofoam boxes sprouting wires and a steel rod that uses a super-cold liquid, a cryogen, to measure humidity more accurately at high altitudes than other instruments can (TT, Aug. 19).The information on how water and temperature interact in the atmosphere above the tropics will help scientists make more accurate computer models for weather patterns and understand the atmosphere’s tantrums, such as hurricanes.University of Colorado research scientist Holger Vömel has been releasing balloons throughout the tropics for years, and said his work in Costa Rica during its rainy season revealed one surprise: the air continues to shed moisture even after it has risen above the level of mixing.TEMPERATURE drops with altitude from sea level to 15 km, and air rises that distance in about two hours. When it strikes the point at which the temperature begins to rise – the boundary between the troposphere below and the stratosphere above, called the tropopause – it cannot rise as quickly and usually sinks, creating convection that mixes air from the ground to the stratosphere. Air can take as long as six months to cross the gap between 16 and 20 kilometers above sea level, Vömel said.With altitude, air steadily cools and loses its capacity to hold moisture, meaning humidity decreases.What surprised Vömel was the discovery that the air continued to dry for one kilometer even after it passed the boundary into the stratosphere.Henry Selkirk, the NASA coordinator of the Ticosonde program and a researcher with the California-based Bay Area Environmental Research Institute, noted a pattern of regular waves in the lower stratosphere that affected the air humidity in the zone Vömel spoke of.“In 2004 we noticed high-frequency gravity waves – buoyancy waves that had a big impact on the saturation point of water vapor at the tropopause,” he said.The implications of the discovery are unknown.“IT’S a difficult problem to model –there’s not much data. It’s difficult to monitor (what goes on in the tropics).We’re sort of in the dark. Every bit of information we can get about it, we need,” he said.Another pattern mystifies scientists as well: researchers in Boulder, Colorado, noted an increase in global atmospheric humidity during the first 20 years of measurement, then a decrease over the last five years, continuing today. But, Vömel said, nobody knows why.The upcoming phase of balloon releases at points throughout the tropics beginning in January might shed light on the mystery, he said, as well as supply more information to Selkirk that could help scientists understand the cause of the waves in the tropopause.THE information Ticosonde gathers is compared to the measurements taken by Aura, a NASA observation satellite, and the U.S. Air Force’s network of satellites in the Defense Meteorological Satellite Program (DMSP). Because they are in the air they are reporting on, the balloons provide on-the-scene information, called in situ in Latin scientists’ jargon, as opposed to the satellite’s remote sensing from above the atmosphere. The balloons’ measurements are more reliable and are used to cross-check the satellites.Also in the skies above Costa Rica, NASA and other U.S. research planes decked with sensors from nose-cone to wingtip have gathered similar kinds of information in the quest to understand hurricanes and other weather phenomena (TT, July 1, 2005).
