Vertical draft
Encyclopedia
An updraft or downdraft is the vertical movement of air as a weather
related phenomenon. One of two forces causes the air to move. Localized regions of warm or cool air will exhibit vertical movement. 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 as subsidence
. This movement of large volumes of air, especially when regions of hot, wet air rise, can create large cloud
s, and is the main cause of thunderstorms. Drafts can also be created 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 then attract air from the surrounding area, which will move towards the center and sink, creating a downdraft.
Updrafts and downdrafts, along with wind shear
in general, are a major contributor to airplane crashes during takeoff and landing in a thunderstorm. Extreme cases, known as downburst
s and microburst
s can be deadly and difficult to predict or observe. The crash of Delta Air Lines Flight 191
on its final approach before landing at Dallas/Fort Worth International Airport in 1985 was presumably caused by a microburst, and prompted the Federal Aviation Administration
(FAA) to research and deploy new storm detection radar stations at some of the major airports, notably the ones in the South, Midwest, and Northeast United States where wind shear contributes to air safety
. Downbursts can cause extensive localized damage, similar to that caused by tornado
es. 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.
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
related phenomenon. One of two forces causes the air to move. Localized regions of warm or cool air will exhibit vertical movement. 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 as subsidence
Subsidence (atmosphere)
Subsidence in the Earth's atmosphere is most commonly caused by low temperatures: as air cools, it becomes denser and moves towards the ground, just as warm air becomes less dense and moves upwards...
. This movement of large volumes of air, especially when regions of hot, wet air rise, can create large cloud
Cloud
A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...
s, and is the main cause of thunderstorms. Drafts can also be created 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 then attract air from the surrounding area, which will move towards the center and sink, creating a downdraft.
Updrafts and downdrafts, along with wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
in general, are a major contributor to airplane crashes during takeoff and landing in a thunderstorm. Extreme cases, known as downburst
Downburst
A downburst is created by an area of significantly rain-cooled air that, after reaching ground level, spreads out in all directions producing strong winds. Unlike winds in a tornado, winds in a downburst are directed outwards from the point where it hits land or water...
s and microburst
Microburst
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. There are two types of microbursts: wet microbursts and dry microbursts...
s can be deadly and difficult to predict or observe. The crash of Delta Air Lines Flight 191
Delta Air Lines Flight 191
Delta Air Lines Flight 191 was an airline service from Fort Lauderdale, Florida's Fort Lauderdale-Hollywood International Airport, bound for Los Angeles International Airport in Los Angeles, California, by way of Dallas-Fort Worth International Airport...
on its final approach before landing at Dallas/Fort Worth International Airport in 1985 was presumably caused by a microburst, and prompted the Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
(FAA) to research and deploy new storm detection radar stations at some of the major airports, notably the ones in the South, Midwest, and Northeast United States where wind shear contributes to air safety
Air safety
Air safety is a term encompassing the theory, investigation and categorization of flight failures, and the prevention of such failures through regulation, education and training. It can also be applied in the context of campaigns that inform the public as to the safety of air travel.-United...
. Downbursts can cause extensive localized damage, similar to that caused by tornado
Tornado
A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...
es. 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.
See also
- Terminal Doppler Weather RadarTerminal Doppler Weather RadarTerminal Doppler Weather Radar is a doppler weather radar system used primarily for the detection of hazardous wind shear conditions on and near major airports in the United States. As of 2011, there were 48 active radars, across the United States & Puerto Rico. Several more radars have also been...
, a 5 cm Doppler radar design to detect wind shear near major airports in the U.S. (FAA) and abroad - NEXRADNEXRADNEXRAD or Nexrad is a network of 159 high-resolution Doppler weather radars operated by the National Weather Service, an agency of the National Oceanic and Atmospheric Administration within the United States Department of Commerce...
, a 10 cm radar in the U.S. that doesn't detect wind shear (NOAA's National Weather ServiceNational Weather ServiceThe National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...
) - Low level windshear alert systemLow level windshear alert systemA Low level windshear alert system measures wind speed and direction at remote sensor station sites situated around an airport.Each equipped airport may have as few as 6 or as many as 32 remote anemometer stations. The remote sensor data received is transmitted to a master station, which generates...
- Atmospheric thermodynamicsAtmospheric thermodynamicsAtmospheric thermodynamics is the study of heat to work transformations in the earth’s atmospheric system in relation to weather or climate...
- Lee wavesLee wavesIn meteorology, lee waves are atmospheric standing waves. The most common form is mountain waves, which are atmospheric internal gravity waves...
- New Zealand National Airways Corporation Flight 441New Zealand National Airways Corporation Flight 441New Zealand National Airways Corporation Flight 441 was a scheduled flight of New Zealand's National Airways Corporation from Whenuapai to Tauranga. On 3 July 1963 at approximately 9:09 am NZST the flight, a Douglas DC-3 Skyliner, flew into a vertical rock face in the Kaimai Ranges near Mount...
— airplane crash linked to severe downdraft - Rear flank downdraftRear flank downdraftThe rear flank downdraft or RFD is a region of dry air wrapping around the back of a mesocyclone in a supercell thunderstorm. These areas of descending air are thought to be essential in the production of many supercellular tornadoes...
and front flank downdraft - ThermalThermalA thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...