Microburst
From Wikipedia, the free encyclopedia
A microburst is a very localized column of sinking air, producing damaging divergent and straight winds at the surface that are similar to but distinguishable from tornadoes which generally have convergent damage.
[edit] History of Term
The term was defined by severe weather expert Tetsuya Theodore Fujita as affecting an area 4 km (2.5 mi) in diameter or less, distinguishing them as a type of downbursts and apart from common wind shear which can encompass greater areas. Dr. Fujita also coined the term macroburst for downbursts larger than 4 km (2.5 mi).
A distinction can be made between a wet microburst which consists of precipitation and a dry microburst which consists of virga. They generally are formed by precipitation-cooled air rushing to the surface, but they perhaps also could be powered from the high speed winds of the jet stream deflected to the surface in a thunderstorm (see downburst).
Microbursts are recognized as capable of generating wind speeds higher than 75 m/s (168 mph; 270 km/h).
[edit] Danger to aircraft
See also: downbursts
The scale and suddenness of a microburst makes it a great danger to aircraft, particularly those at low altitude which are taking off and landing. The following are some fatal crashes that have been attributed to microbursts in the vicinity of airports:
A microburst often causes aircrafts to crash when they are attempting to land. The microburst is an extremely powerful gust of air that, once hitting the ground, spreads in all directions. As the aircraft is coming in to land, the pilots try to slow the plane to an appropriate speed. When the microburst hits, the pilots will see a large spike in their airspeed, caused by the force of the headwind created by the microburst. A pilot inexperienced with microbursts would try to decrease the speed. The plane would then travel through the microburst, and fly into the tailwind, causing a sudden decrease in the amount of air flowing across the wings. The sudden loss of air moving across the wings causes the aircraft to literally drop out of the air. The best way to deal with a microburst in an aircraft would be to increase speed as soon as the spike in airspeed is noticed. This will allow the aircraft to remain in the air when traveling through the tailwind portion of the microburst and also pass through the microburst with less difficulty.
[edit] List of microbursts
Hickory Hills, IL (Cook County) - 9:50pm Monday, October 2, 2006 large microburst, windspeeds of 75+ mph, damaged many homes, small businesses, and tore the roof off of H.H. Conrady Jr. High and landed on a van. Power outages in the sum of 170,000+ for over 24 hours in the Chicagoland area due to trees falling on top of powerlines. Numerous trees uprooted, blocking roads and shutting down roads. Several roads were closed, including 2 major highways due to flooding.
Berwyn/Cicero, IL (Cook County) - 5:20am Saturday July 5, 2003. rather large microburst. winds estimated in cicero at 60-65 miles per hour. many trees/tree branches down, roads blocked, a jeep in berwyn destroyed when a 50 foot limb came down on it, crushing the rear left side of its roof in, and completely barricading the street. many power outages. report of a century plus old oak tree toppled near the lakeshore.
Alexandria Bay, NY (Jefferson County) - 4:20am Saturday, July 15, 1995 large microburst, windspeeds of 100+ mph, damaged many homes and businesses. Many trees were uprooted or broken in half, Welesley Island State Park was evacuated and closed, The American Span Thousand Islands suspension bridge was closed. Visit http://marcmny.tripod.com/jeffco5.htm for more information.
Marion, IL The Nov. 19, 1991 a microburst in Marion destroyed or severely damaged about 75 homes, four businesses, a fire station and the high school. Damage was estimated at $10 million
A microburst squall with windspeeds of 80mph is responsible for capsizing and sinking the Pride of Baltimore in May 1986 in the Caribbean, about 250 miles north of Puerto Rico. The ship took the lives of her captain and 3 of her other 11 crew members.
A particularily violent microburst is a possible alternative explanation to the 1961 sinking of the American school brigantine Albatross. The ships captain Dr. Christopher Sheldon claimed that the ship was hit by a white squall on the voyage from Progreso, Mexico to Nassau in the Bahamas.
[edit] References
[edit] Printed Media
- Fujita, T.T. (1981). "Tornadoes and Downbursts in the Context of Generalized Planetary Scales". Journal of the Atmospheric Sciences, 38 (8).
- Fujita, T.T. (1985). "The Downburst, microburst and macroburst". SMRP Research Paper 210, 122 pp.
- Wilson, James W. and Roger M. Wakimoto (2001). "The Discovery of the Downburst - TT Fujita's Contribution". Bulletin of the American Meteorological Society, 82 (1).
