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April 1999

WISP goes to Mt. Washington

Ice is synonymous with New England's imposing Mt. Washington. "Some of the very earliest icing research was done there back in the thirties and forties. Everything gets iced up--it's just legendary for that." says Marcia Politovich (Research Applications Program).

Marcia is director of a field project in April that will focus radars, radiometers, snow gauges, and mobile soundings on New England's highest mountain. The Mt. Washington Winter Icing and Storms Project (MWISP) borrows its name from WISP, which carried out four seasons of successful icing research in northeastern Colorado earlier this decade. Both WISP and MWISP have been funded largely by the FAA, for whom RAP has been developing better forecasts of in-flight icing. MWISP is also being supported by NASA, the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL), and the Mt. Washington Observatory (MWO).

The same factors that make Mt. Washington an improbable tourist destination in April--persistent clouds, frequent freezing rain--make it a great site for icing research. The summit is enclosed in cloud 61% of the time during an average April. "It's a wonderful cloud lab," says Marcia.

Leading the field aspects of MWISP are Marcia, Chuck Ryerson (CRREL), and Ken Rancourt (MWO). MWISP will be the largest field program ever conducted through the observatory, which has just launched a Center for Wind, Ice, and Fog Research.

Previous WISP projects relied heavily on aircraft to take data from the middle of icing-prone areas. This time NASA Glenn Research Center (formerly the Lewis Research Center at Lewis Field, Ohio) will fly its heavily instrumented Twin Otter aircraft out of Portland, Maine, for two weeks. RAP's Ben Bernstein and Frank McDonough will help coordinate the flights with ground-based sensors. The Twin Otter will provide in-situ measurements to confirm what the remote sensors are detecting from the ground below the peak and to compare with similar measurements from the summit. One goal is to document a cloud's uniformity in time and space. "If the cloud is highly uniform, then it can be assumed that differences can be neglected," explains the MWISP science plan.

The leaders of MWISP (left to right): Chuck Ryerson (U.S. Army Cold Regions Research and Engineering Laboratory), Marcia Politovich (NCAR), and Ken Rancourt (Mt. Washington Observatory).

The aviation community will be watching as MWISP examines freezing drizzle and, especially, freezing rain. "Much of the research and development of operational forecasting tools on supercooled large drops has focused on freezing drizzle and ignored freezing rain," says Ben, who has analyzed a noteworthy case from February 1998. In that incident, NASA's Twin Otter endured over 90 minutes of exposure to freezing rain above the Midwest. "The ice that accreted on the aircraft resulted in significant performance degradation, including a decrease in climb capability, a 60 to 200 percent increase in drag, and a 30 percent decrease in the coefficient of lift," says Ben. According to Marcia, "This is one of the first documentations of the effect of freezing rain on flight over an extended period."

A polarimetric scanning radiometer from NOAA's Environmental Technology Laboratory (ETL) will monitor clouds from the summit. Many of the other instruments will be deployed near Breton Woods, a few miles west of the peak, at the base of a cog railway that brings summer tourists to the Mt. Washington summit. Instruments here will include K- and W-band radars from the University of Massachusetts, K- and X-band radars and a second radiometer from NOAA/ETL, and other equipment from NASA, the FAA, and CRREL. The radar and radiometer output will be monitored by RAP's Jothiram Vivekanandan and Guifu Zhang, who are developing techniques that use combinations of remote sensors to estimate supercooled liquid water content and average droplet size. They will use polarimetric radar data to distinguish between spherical droplets and nonspherical ice particles.

Radiosondes will be launched from various points upstream by RAP's mobile CLASS (cross-chain Loran atmospheric sounding system). It will be the most distant deployment from Boulder to date for the mobile rawinsonde system. Jeff Cole will be on hand to operate CLASS, with additional help coming from CRREL. Students at nearby Plymouth State and Lyndon State Colleges will provide forecasting support.

A forest of antennas rises above the summit of Mt. Washington, a tourist mecca in summer but an ice-locked outpost in winter. The building in the foreground is called the Tip-Top House. Built in 1853 and recently restored, it once housed a hotel and the first daily newspaper published from a mountaintop. A larger building just to its northeast hosts summer visitors. Left: wind and rime combine to paint a wintry picture at the Mt. Washington summit. (Photos courtesy Brooks Martner, NOAA.)

The soundings and other standard meteorological data will help MWISP scientists make sense out of what they're observing at the summit. The goal is to improve the algorithms used in weather models to predict in-flight icing over large areas. Few tests have been done for supercooled clouds with relatively high liquid-water content. Such clouds are rare during Colorado winters but are expected to predominate at Mt. Washington. The ideal, says Marcia, would be "fairly thick, nonprecipitating cloud--but not too thick--nice and uniform, with a base below the summit and a top above the summit."

Real-time runs of the Penn State/NCAR mesoscale forecast model, version 5 (MM5) will be extended from a Midwest experiment to include the MWISP study area during April. Jim Bresch (MMM) and Greg Thompson (RAP) are leading the real-time modeling effort.

"We'll be using measurements from the observatory to do some more detailed work with the microphysics in the MM5 model," says Marcia. Pilot reports can be used for long-term, large-scale comparisons with the model. However, "to start getting down to smaller scales, like the terminal area around airports, we need smaller-scale measurements with more detail than just 'yes' or 'no' for icing." A better icing algorithm is expected to become part of the upcoming Weather Research and Forecast model being created by NCAR, NOAA, and the University of Oklahoma.

MWISP will be in session during an auspicious anniversary. On 12 April 1934, Mt. Washington recorded a wind gust of 231 miles per hour (103 meters per second), still the highest surface speed ever recorded anywhere. Marcia got a taste of the summit's windy ways as she joined an instrument-siting trip in January. "It was clear but only about 5 degrees [Fahrenheit], with winds of 50 to 55 knots and gusts to 63 [or about 72 mph]. We had to walk all over the roof to figure out where to put instruments. You're really afraid you're going to blow off the other side of the roof, but we managed." •Bob Henson


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Edited by Bob Henson, bhenson@ucar.edu

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