Apr. 20, 1999 BOULDER--Scientists from the National Center for Atmospheric Research (NCAR) are spending April at the Northeast's highest, coldest, and windiest peak, studying dangerous aircraft icing. The Mt. Washington Winter Icing and Storms Project (MWISP) is testing methods for remote sensing and improved prediction of in-flight icing conditions, particularly freezing drizzle and freezing rain, which can down small aircraft. NCAR's primary sponsor is the National Science Foundation (NSF).
New Hampshire's Mt. Washington, best known for its high winds, has a summit enclosed in cloud 61% of the time during an average April. "It's a wonderful late-winter, early-spring cloud lab," says NCAR's Marcia Politovich, who is leading the field observations along with Chuck Ryerson (the U.S. Army Cold Regions Research and Engineering Laboratory, or CRREL) and Ken Rancourt (Mount Washington Observatory, or MWO). In mid-April, the peak saw prolonged snow, cold, and winds gusting above 100 miles per hour. "The fast-moving clouds provide constantly changing conditions that are a challenge for the radars to track," says Politovich. MWISP is the largest field program conducted on the summit, where some of the first research on icing began in the 1930s.
The goal of MWISP is to improve in-flight icing detection, mainly from remote sensors, and to improve forecasts issued by computer models. Pilot reports can be used for long-term, large-scale comparisons with a model. However, "To get down to smaller scales, like the terminal area around airports, we need measurements with more detail than just the pilots' 'yes' or 'no' for icing," says Politovich. Better icing- prediction software is expected to become part of the Weather Research and Forecast model being created by NCAR, the National Oceanic and Atmospheric Administration (NOAA), and the University of Oklahoma.
The National Aeronautics and Space Administration (NASA) Glenn Research Center is flying its Twin Otter aircraft through clouds above the mountain's summit. NCAR is joining NOAA, CRREL, and Quadrant Engineering to analyze data from remote sensors and compare the results with on-site measurements from the summit and aircraft. The remote sensors include a five-channel, fully polarimetric radiometer at the summit that will sense radiation emitted by clouds. Deployed a few miles west of the peak, near Bretton Woods, are X-, K-, and W-band radars, a lidar (laser- emitting radar), and a second multichannel radiometer. Balloon-borne weather instruments are being launched from various points by a mobile unit from NCAR, and Plymouth State and Lyndon State colleges are providing weather forecasts.
The researchers are developing techniques that use combinations of remote sensors to analyze supercooled droplets and ice crystals. These droplets remain liquid, even with air temperatures below freezing, until they encounter a surface on which to freeze (such as an airplane's wing).
The aviation community is watching as MWISP examines freezing drizzle and freezing rain. According to NCAR's Ben Bernstein, "Much of the research and development of operational forecast tools on supercooled drops has focused on freezing drizzle and ignored freezing rain." Bernstein has analyzed a case from February 1998 in which the same NASA Twin Otter aircraft now flying in MWISP suffered over 90 minutes of exposure to freezing rain above the Midwest. The result was a major degradation of the plane's performance, including an increase in drag of up to 200%.
MWISP is funded largely by the Federal Aviation Administration (FAA) to improve forecasts of in-flight icing. The NCAR portion of this research is sponsored by NSF through an interagency agreement in response to requirements and funding by the FAA's Aviation Weather Research Program. Also funding MWISP are NASA, CRREL, and MWO. Providing instruments are NOAA's Environmental Technology Laboratory; the University of Massachusetts; the Defense Research Establishment at Val Cartier, Canada; ATEK Data Corporation; and Stratton Park Engineering. NCAR is managed by the University Corporation for Atmospheric Research, a consortium of more than 60 universities offering Ph.D.s in atmospheric and related sciences.
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