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Science Briefing

Thunderstorms are one of the classic challenges of short-term weather prediction. Sometimes only a small variation in temperature or moisture is enough to produce severe thunderstorms on an otherwise placid day. Using an NCAR-based computer model and field observations, Andrew Crook (RAP/MMM) has found that the increments of temperature and moisture needed to tip the balance toward storm genesis can be smaller than the error range in current observations. Andrew recently presented his findings in San Francisco, California, at the American Meteorological Society's 18th Conference on Severe Local Storms.

Andrew Crook. (Photo by Carlye Calvin.)
To explore the potential for storm prediction, Andrew performed a number of so-called forward sensitivity experiments. These evaluate the difference in how a certain weather situation evolves, given a slight variation in the initial state of the model. Wind, temperature, and moisture values were derived from surface, radar, and radiosonde observations, and from a technique developed by Andrew and John Tuttle (MMM/RAP) for tracking Doppler radar signals.

On average, the various data sources had temperature errors in the range of 1 degree C and errors in mixing ratio (water vapor concentration) of around one gram per kilogram (g/kg). The latter is roughly 10% of the water vapor present on a humid Colorado day. In the model's standard scenario, Andrew found that a temperature decrease of 1 degree C was enough to shut off storm development entirely, while a 1 degree C increase led to a fourfold increase in rainfall. Similarly, rainfall dropped by 80% when mixing ratios were lowered by the standard error of 1 g/kg, while it more than doubled for a 1 g/kg increase.

"Predicting thunderstorm initiation and motion is one of the most difficult problems facing operational weather forecasters," notes Andrew. "These results have begun to uncover part of the reason for this difficulty--thunderstorm development is very sensitive to variations in low-level temperature and moisture which are within typical observational variability."

Those who study atmospheric technology in community colleges will enjoy the latest in educational technology, thanks to a recently announced $450,000 grant to be awarded later this year to the Desert Research Institute (DRI) for development work with COMET's Educational Resources Center (ERC). The three-year grant from NSF's Division of Undergraduate Education will produce interactive CD-ROM modules to train college students in instrumentation, field project design, and measurement principles. Also included are workshops for community college faculty to help them integrate the modules with field measurement experience.

Melanie Wetzel. (Photo by Carlye Calvin.)
The principal investigator is Melanie Wetzel, an assistant research professor at DRI. Melanie has been on sabbatical at COMET for the past year. Collaborating with her will be Brian Heckman, head of the COMET ERC; Randolph Borys (DRI); and faculty from the multicampus Colorado Mountain College. "We've been working with the Colorado Mountain College for some time through DRI's Storm Peak Laboratory," says Melanie. "The mountaintop field research lab is collocated with the college's Alpine Campus near Steamboat Springs."

Established last fall, the COMET ERC is designed to help export the program's skills in multimedia education to new venues. "We are very proud of this achievement, the first--I hope--of many collaborative efforts with universities," says COMET director Tim Spangler. "We are glad the National Weather Service has had the vision to support the ERC and to see the value of university-NWS partnerships to improve our country's meteorological education."

Ray Roble. (Photo by Carlye Calvin.)
Twenty-five years of research by HAO senior scientist Ray Roble are being recognized in a prestigious national honor. On 29 April, Ray received the Arctowski Medal of the National Academy of Sciences at a ceremony in Washington. The prize includes a $20,000 award to Ray and $60,000 to support research of his choice in solar/terrestrial relations. The Arctowski Medal is given every three years; among the past recipients are former HAO scientist Jack Eddy.

Ray was cited by the NAS for his "indispensable contributions to understanding the effects of variable solar inputs on the earth's atmosphere and ionosphere by powerful global modeling techniques."

A native of Michigan, Roble completed his doctorate in aeronomy at the University of Michigan in 1969. Shortly afterward, he came to NCAR as a postdoctoral researcher and began work on the computer model that has since become his crowning achievement: the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM). (See the January issue of Staff Notes Monthly, available on the Web at http://home.ucar.edu/ucargen/UCARnewstext.html, for details.) Ray became an NCAR senior scientist in 1978 and now heads the HAO Terrestrial Impacts of Solar Output section.

Was Ray surprised by the honor? "Completely! I now remember that Jack Eddy received the award about ten years ago, but I was not aware that it still existed. It is certainly an honor for me as well as for HAO, NCAR, and UCAR." He anticipates the prize will be used to promote and enhance solar/terrestrial research at NCAR.

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Edited by Bob Henson, bhenson@ucar.edu
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Last revised: Thu Mar 30 11:51:03 MST 2000