Mt. Washington's Wild Weather Sheds Light on Aircraft Icing

New Hampshire's Mt. Washington, best known for its high winds, has asummit enclosed in cloud 61% of the time during an average April. "It'sa wonderful late-winter, early-spring cloud lab," says NCAR's MarciaPolitovich, who is leading the field observations along with ChuckRyerson (the U.S. Army Cold Regions Research and Engineering Laboratory,or CRREL) and Ken Rancourt (Mount Washington Observatory, or MWO). Inmid-April, the peak saw prolonged snow, cold, and winds gusting above100 miles per hour. "The fast-moving clouds provide constantly changingconditions that are a challenge for the radars to track," saysPolitovich. 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 fromremote sensors, and to improve forecasts issued by computer models.Pilot reports can be used for long-term, large-scale comparisons with amodel. However, "To get down to smaller scales, like the terminal areaaround airports, we need measurements with more detail than just thepilots' 'yes' or 'no' for icing," says Politovich. Better icing-prediction software is expected to become part of the Weather Researchand Forecast model being created by NCAR, the National Oceanic andAtmospheric Administration (NOAA), and the University of Oklahoma.

The National Aeronautics and Space Administration (NASA) Glenn ResearchCenter is flying its Twin Otter aircraft through clouds above themountain's summit. NCAR is joining NOAA, CRREL, and Quadrant Engineeringto analyze data from remote sensors and compare the results with on-sitemeasurements from the summit and aircraft. The remote sensors include afive-channel, fully polarimetric radiometer at the summit that willsense radiation emitted by clouds. Deployed a few miles west of thepeak, near Bretton Woods, are X-, K-, and W-band radars, a lidar (laser-emitting radar), and a second multichannel radiometer. Balloon-borneweather instruments are being launched from various points by a mobileunit from NCAR, and Plymouth State and Lyndon State colleges areproviding weather forecasts.

The researchers are developing techniques that use combinations ofremote sensors to analyze supercooled droplets and ice crystals. Thesedroplets remain liquid, even with air temperatures below freezing, untilthey encounter a surface on which to freeze (such as an airplane'swing).

The aviation community is watching as MWISP examines freezing drizzleand freezing rain. According to NCAR's Ben Bernstein, "Much of theresearch and development of operational forecast tools on supercooleddrops has focused on freezing drizzle and ignored freezing rain."Bernstein has analyzed a case from February 1998 in which the same NASATwin Otter aircraft now flying in MWISP suffered over 90 minutes ofexposure to freezing rain above the Midwest. The result was a majordegradation of the plane's performance, including an increase in drag ofup to 200%.

MWISP is funded largely by the Federal Aviation Administration (FAA) toimprove forecasts of in-flight icing. The NCAR portion of this researchis sponsored by NSF through an interagency agreement in response torequirements and funding by the FAA's Aviation Weather Research Program.Also funding MWISP are NASA, CRREL, and MWO. Providing instruments areNOAA's Environmental Technology Laboratory; the University ofMassachusetts; the Defense Research Establishment at Val Cartier,Canada; ATEK Data Corporation; and Stratton Park Engineering. NCAR ismanaged by the University Corporation for Atmospheric Research, aconsortium of more than 60 universities offering Ph.D.s in atmosphericand related sciences.

-The End-

Note to Editors/Reporters: Images pertaining to this release are available via theInternet using anonymous ftp: Log on to ftp.ucar.edu using the userid:anonymous; password: [your e-mail address]; directory: /communications[include the slash]; filename: wisp1.tif, wisp2.tif, wisp3.tif.