Vertical draft
Inmeteorology,anupdraft(British English:up-draught) is a small-scalecurrentof rising air, often within a cloud.[1]
Overview
[edit]Vertical drafts, known as updrafts or downdrafts, are localized regions of warm or cool air that move vertically. A mass of warm air will typically be less dense than the surrounding region, and so will rise until it reaches air that is either warmer or less dense than itself. The converse will occur for a mass of cool air, and is known assubsidence.This movement of large volumes of air, especially when regions of hot, wet air rise, can create largeclouds,and is the central source ofthunderstorms.Drafts can also be caused by low or high pressure regions. A low pressure region will attract air from the surrounding area, which will move towards the center and then rise, creating an updraft. A high pressure region will attract air from the surrounding area, which will move towards the center and sink, spawning adowndraft.
Updrafts and downdrafts, along withwind shearin general, are a major contributor to airplane crashes during takeoff and landing in a thunderstorm. Extreme cases, known asdownburstsand microbursts, can be deadly and difficult to predict or observe. The crash ofDelta Air Lines Flight 191on its final approach before landing atDallas/Fort Worth International Airportin 1985 was presumably caused by a microburst, and prompted theFederal Aviation Administration(FAA) to research and deploy new storm detection radar stations at some of the major airports, notably those in the South, Midwest, and Northeast United States where wind shear affectsair safety.Downbursts can cause extensive localized damage, similar to that caused bytornadoes.Downburst damage can be differentiated from that of a tornado because the resulting destruction is circular and radiates away from the center. Tornado damage radiates inward, towards the center of the damage.
The term "downdraft" can also refer to a type ofbackdraftwhich occurs through chimneys which have fireplaces on the lowermost levels (such as basements) of multi-level buildings. It involves cold air coming down the chimney due to low air pressure, and makes it hard to light fires, and can push soot andcarbon monoxideinto domiciles.
See also
[edit]- Terminal Doppler Weather Radar,a 5 cmDoppler weather radardesign to detect wind shear near major airports in the U.S. (FAA) and abroad
- NEXRAD,a 10 cm radar in the U.S. that detects wind shear, but to a specific extent. (NOAA'sNational Weather Service)
- Low level windshear alert system
- Atmospheric thermodynamics
- Lee waves
- New Zealand National Airways Corporation Flight 441— airplane crash linked to severe downdraft
- Rear flank downdraftandforward flank downdraft
- Thermal
References
[edit]- ^Park, Chris (2007).A Dictionary of Environment and Conservation(1 ed.). Oxford:Oxford University Press.doi:10.1093/acref/9780198609957.001.0001.ISBN9780198609957.Retrieved14 August2014.
External links
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