Weather forecasting has come a long way since the era of dog-eared almanacs and barn-door barometers. Nowadays, numerical models running on the world’s most powerful supercomputers crunch data from a host of sources that include ground-based weather stations, radar, aircraft, and satellites. But one key type of information—vertical profiles of how temperature, pressure, and water vapor vary through the atmosphere—is still gathered the same way it has been since the 1930s: with weather balloons.
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That may be about to change, thanks to six simple satellites collectively known as Cosmic, due for launch in mid-April. Each carries a Global Positioning System (GPS) receiver, a communications link to the ground, and not much else. The receivers will lock onto transmissions from the U.S. Air Force’s constellation of 24 GPS satellites and watch how the atmosphere bends the radio waves. From that information, each Cosmic spacecraft can get a vertical profile of the atmosphere’s temperature, pressure, and water content above one spot on Earth’s surface with surprising accuracy and vertical resolution. All together, the fleet will make 3000 “soundings†a day, evenly distributed across the globe.
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For atmospheric scientists used to large, expensive Earth-observation satellites operated by the likes of the U.S. National Oceanic and Atmospheric Administration and EUMETSAT, Europe’s weather satellite operator, GPS sounding is an unknown quantity. “For most, it is still a strange idea from out in the wilderness,†says sounding pioneer Thomas Yunck of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. But he predicts Cosmic data will be “far beyond anything we have imagined†and will lead to a “major sea change in atmospheric sensing.†Healy agrees: “When people see the data and the quality of it, they will be won over.â€
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With funding from various U.S. agencies, UCAR has worked hard to streamline the processing so that the data can reach forecasters as soon as possible. With ground stations in Fairbanks, Alaska, and Kiruna, Sweden, each of the satellites can download data once per 100-minute orbit. Transfer to Boulder takes 5 minutes, and processing takes 10 to 15 minutes, so Kuo predicts that data can be in the hands of weather agencies on average 90 minutes after the sounding was made. The U.S. National Centers for Environmental Prediction, ECMWF, and the U.K. Met Office hope to start receiving the data a couple of months after Cosmic is launched. “Researchers love this stuff and are well prepared for the data,†says Yunck.[/b]
