__NOTOC__ A microburst is a very localized column of sinking air, producing damaging divergent and straight-line winds at the surface that are similar to but distinguishable from tornadoes which generally have convergent damage.

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 precipitaiton 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).

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:

• Delta Air Lines Flight 191
• Eastern Air Lines Flight 66
• Pan Am Flight 759
• USAir Flight 1016

A microburst often causes aircraft to crash when they are attempting to land. The microburst is anu 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 in microbusts would try to decrease the speed. The plane would then travel through the microburst, and fly into the tailwind, causing a decrease in airspeed. 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.

References

• 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).

See also

• Air safety
• Downdraft

External links and sources

• The Semi-official Microburst Handbook Homepage (NOAA)
• Microbursts (WW2010) (University of Illinois at Urbana-Champaign)
• Taming the Microburst Windshear (NASA)
• StormWiki

Severe weather and convection | Winds | Storms | Weather hazards | Aviation risks