Minutes of the September 22, 2008 Meeting
Smoky Mountain AMS Chapter
A few people met first for dinner at Calhoun's on the River in Knoxville, and then around 15 people convened for the meeting in the Plant Biotech Bldg. on the UT Ag campus. David Hotz (Science and Operations Officer at the National Weather Service in Morristown) spoke about microbursts. The following was a synopsis of his talk:
"Microbursts are small downbursts, less than 4 km in outflow size, with peak winds lasting only 2 to 5 minutes. They can be classified as micro or macro-bursts, and also either wet or dry microbursts (Fujita, 1985). All microbursts are characterized by a vertical downrush of air with a divergent outflow at its base. Strong, concentrated downdrafts from convective showers and thunderstorms (downbursts; Fujita 1985) have caused a number of commercial passenger jets to crash on attempted takeoffs and landings (see also Fujita and Byers 1977; Fujita and Caracena 1977). Microbursts also pose hazards to small sailboats that are capsized by sudden-shifting, strong winds, and to those fighting forest fires, who may be suddenly engulfed in a fire storm fanned up in an unexpected direction by a microburst.
Most origin theories credit thermodynamic factors with microburst creation. Wolfson (1983) contends that microbursts result from dynamically induced vertical pressure gradients that are intrinsic characteristics of strong mesocyclone circulation. There are several forecasting tools and techniques to determine the potential of microbursts, such as WINDEX and looking for mid-level dry air. Doppler radar is the primary tool for detecting and observing microbursts."
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