|
 |
|
|
|
Weather ObservingBefore anyone can predict the weather for tomorrow or project the climate for 2050, they need a solid picture of the atmosphere as it now stands. NCAR and UOP help fill that need by developing state-of-the-art instruments to monitor the air and its many qualities. Many of these sensors are available to scientists worldwide. Digital instruments and sensor networks
The basic weather instruments invented during the Renaissance and then continually refined were transformed yet again into digital tools starting in the 1970s. Scientists can now track temperature and wind speed by measuring sound waves as they travel between two closely spaced sensors. Moisture can be detected by seeing how much of a beam of ultraviolet light gets absorbed by water vapor. These and many other sensors—created at NCAR and elsewhere—are a standard part of the center's Integrated Surface Flux Facility. Specially configured versions of the facility are deployed on field expeditions around the world, helping scientists analyze relationships between the atmosphere, biosphere, and geosphere—connections that can vary greatly in space and time. For example, two soil samples only inches apart may differ dramatically but might not change for years, whereas the atmosphere can be quite similar over several miles but change locally within seconds. The facility's flexible array of sensors can tackle these small-scale changes, measuring everything from the thermal properties of soil to the movement of carbon dioxide in turbulent air.. Upper atmosphere toolsUsed widely since the 1930s, weather balloons carrying sophisticated meteorological sensors (called radiosondes ) are still an integral tool for measuring conditions up to altitudes of 18 miles (30 kilometers) or more. At these heights, powerful winds help shape the destiny of surface weather features. NCAR provides radiosondes for field projects through Mobile GAUS, its GPS Advanced Upper-Air Sounding System. Transported to field sites in a trailer or aboard a pickup truck, the system allows a single person to launch weather balloons and monitor data sent back via radio as each balloon rises. Radiosondes suspended from parachutes and dropped from aircraft to study the lower atmosphere are called dropsondes or dropwindsondes. 
GAUSS also features a tethersonde system, called TAOS. It includes a balloon that perches as high as 3,200 feet (1,000 meters) while instruments along its tethering line sample the atmosphere every second. Another key upper-atmosphere tool is the Integrated Sounding System. These systems combine a Mobile GAUS unit with a standard surface weather station and a UHF wind profiler—a small radar that measures wind, temperature, rain, and snow aloft. To suit the phenomena being studied, each system can be configured to include other tools. A mobile version allows for rapid deployment in advance of storms. Despite their benefits, radiosondes are expensive to deploy, and few can be launched above the world's oceans. Scientists now have a powerful new technique for measuring the upper atmosphere, one that also makes use of GPS. In 1995, UOP researchers and partners deployed a satellite-borne receiver that intercepts GPS signals after they pass in and out of Earth's atmosphere. By measuring tiny delays in these signals, scientists can infer temperature and moisture along the signal path. Ground-based GPS receivers provide water-vapor data using a similar method. The GPS technique is proving its worth from space in a U.S.-Taiwan collaboration: the Constellation Observing System for Meteorology, Ionosphere and Climate. Six COSMIC satellites, launched in 2006, are providing a rich portrait of weather conditions aloft. COSMIC is also furnishing data on the electrically charged ionosphere high above ground. Another new high-level probe is the driftsonde, tested by NCAR in the summer of 2006. Driftsondes use thin polyethylene balloons to lift a payload of up to 20 dropsondes to a height of 10 miles (16 km) or more. They can stay at that altitude for five to six days, drifting in the prevailing stratospheric winds and releasing dropsondes along the way. Driftsondes could greatly enhance weather observing above remote oceans. Aerosondes, miniature aircraft guided by remote control, are being adapted for atmospheric research by scientists and engineers at UCAR member universities. These relatively inexpensive craft are being tested in extreme conditions—for instance, during hurricanes in Florida and over stretches of the frigid Arctic . They hold promise for bringing back data from areas too remote to fly over with conventional aircraft.
|
|||||
Radar
