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Encyclopedia > Mesocyclone

A mesocyclone is a cyclonic vortex of air, between approximately 2 and 10 km diameter within a convective storm. They can often be found in association with updrafts in supercells, where tornadoes may form. The term refers only to mesoscale cyclones found within convective storms, and does not apply to other cyclones on the mesoscale.[1] Storms with mesocyclones can feature strong surface winds and severe hail. Wikipedia does not have an article with this exact name. ... Satellite view of a supercell A supercell is a severe thunderstorm with a deep rotating updraft (a mesocyclone) [1]. Supercell thunderstorms are the largest, most severe class of single-cell thunderstorms. ... Satellite view of a supercell A supercell is a severe thunderstorm with a deep rotating updraft (a mesocyclone) [1]. Supercell thunderstorms are the largest, most severe class of single-cell thunderstorms. ... A tornado in central Oklahoma. ... The term mesoscale is a size scale referring to weather systems smaller than synoptic scale systems but larger than storm-scale systems. ... This does not adequately cite its references or sources. ...

Contents

Definition

A mesocyclone is an area of vertically oriented atmospheric rotation (usually but not always cyclonic) that is most often associated with a localized low pressure region within a severe thunderstorm. The phenomenon is normally relatively localized in nature lying between the synoptic scale (hundreds of kilometers) and small scale (hundreds of meters). A severe thunderstorm is a thunderstorm with winds 58 mph or greater, 3/4 inch or larger hail, or tornadoes. ... The synoptic scale in meteorology (also known as large scale or cyclonic scale) is a horizontal length scale of the order of 1000 kilometres (about 620 miles) or more [1]. This corresponds to a horizontal scale typical of mid-latitude depressions. ...


In layman's terms, the mesocyclone is a rotating updraft within a severe thunderstorm around 5 to 10 miles in diameter, that usually spins in the same direction as low pressure systems for a given hemisphere.


Identification

The word mesocyclone is associated with weather radar terminology. This is because the presence of a mesocyclone is verified by Doppler weather radar. Mesocyclones are most often identified in the right-rear flank of supercell thunderstorms and squall lines, and may be distinguished by a hook echo rotation signature on Doppler weather radar. It has been suggested that Pulse-Doppler radar be merged into this article or section. ... This long range Radar antenna, known as ALTAIR, is used to detect and track space objects in conjunction with ABM testing at the Ronald Reagan Test Site on the Kwajalein atoll[1]. Radar is a system that uses radio waves to determine and map the location, direction, and/or speed... Satellite view of a supercell A supercell is a severe thunderstorm with a deep rotating updraft (a mesocyclone) [1]. Supercell thunderstorms are the largest, most severe class of single-cell thunderstorms. ... A shelf cloud associated with a heavy or severe thunderstorm over Enschede, The Netherlands. ... A classic hook echo. ... It has been suggested that Pulse-Doppler radar be merged into this article or section. ... This long range Radar antenna, known as ALTAIR, is used to detect and track space objects in conjunction with ABM testing at the Ronald Reagan Test Site on the Kwajalein atoll[1]. Radar is a system that uses radio waves to determine and map the location, direction, and/or speed...


Visual cues such as a rotating wall cloud or tornado may also hint at the presence of a mesocyclone. This explains why the term has entered into wider usage in connection with rotating features in severe storms. A wall cloud with tail cloud A wall cloud is a cloud formation. ...


Formation

Wind shear (red) sets air spinning (green).
Wind shear (red) sets air spinning (green).
The updraft (blue) 'tips' the spinning air upright.
The updraft (blue) 'tips' the spinning air upright.
The updraft then starts rotating.
The updraft then starts rotating.

Mesocyclones are believed to form when strong changes of wind speed and/or direction with height ("wind shear") sets parts of the lower part of the atmosphere spinning in invisible tube-like rolls. The convective updraft of a thunderstorm is then thought to draw up this spinning air, tilting the rolls' orientation upward (from parallel to the ground to perpendicular) and causing the entire updraft to rotate as a vertical column. Image File history File links No higher resolution available. ... Wind shear is a difference in wind speed or direction between two points in the atmosphere. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Wind shear is a difference in wind speed or direction between two points in the atmosphere. ...


As the updraft rotates, it may form what is known as a wall cloud. The wall cloud is a spinning layer of clouds descending from the mesocyclone. The wall cloud tends to form closer to the center of the mesocyclone. As the wall cloud descends, a funnel-shaped cloud may form at its center. This is the first stage of tornado formation.


The presence of a mesocyclone is believed to be a key factor in the formation of the strong tornadoes associated with severe thunderstorms. Doppler radar, which can detect the rotation of air within the storm, is currently the best means of detecting mesocyclones.


Another way of thinking of a mesocyclone and tornado formation is to imagine a large rotating thunderstorm in progress. Tornadoes typically form at the peak of thunderstorm intensity as the storms begin to weaken. This is because the momentum and vacuum built up as large masses of air rise into the upper atmosphere causes a siphoning effect nearer to the ground. As the updraft is restricted, the entire thunderstorm is fed by smaller pockets of remaining warm air at the ground. The backpressure generated as the warm air runs out sucks the base of the thunderstorm towards the ground (i.e. a wall cloud). Once the warm air at the ground is nearly depleted, the entire top of the thunderstorm and the large wall cloud siphons air from a 1 mile or less diameter region at the ground, forming a tornado. If a moderate supply of warm air is available ahead of the storm, the storm may be tornadic for some time. If the warm air runs out, then the storms essentially chokes itself off and gradually dies.


See also

Satellite view of a supercell A supercell is a severe thunderstorm with a deep rotating updraft (a mesocyclone) [1]. Supercell thunderstorms are the largest, most severe class of single-cell thunderstorms. ...

References

  1. ^ American Meteorological Society Glossary - Mesocyclone. Allen Press Inc. (2000-06). Retrieved on 2006-12-07.

For the Manfred Mann album, see 2006 (album). ... December 7 is the 341st day (342nd in leap years) of the year in the Gregorian calendar. ...

External links

Cyclones and Anticyclones of the world
v  d  e
Extratropical - Meso-scale - Polar - Polar low - Subtropical - Tropical

  Results from FactBites:
 
Mesocyclone - Wikipedia, the free encyclopedia (319 words)
Mesocyclones are most often identified in the right-rear flank of supercell thunderstorms and squall lines, and may be distinguished by a hook echo or gate-to-gate rotation signature on Doppler weather radar.
Mesocyclones are believed to form when strong changes of wind speed and/or direction with height ("wind shear") sets parts of the lower part of the atmosphere spinning horizontally in invisible tube like rolls.
The presence of a mesocyclone is believed to be a key factor in the formation of the strong tornados associated with severe thunderstorms.
NWS Norman, Oklahoma - Weather Glossary for Storm Spotters (4037 words)
Therefore, a mesocyclone should not be considered a visually-observable phenomenon (although visual evidence of rotation, such as curved inflow bands, may imply the presence of a mesocyclone).
It extends outward from the mesocyclone center, usually toward the south or southwest (but occasionally bows outward to the east or southeast in the case of an occluded mesocyclone), and is characterized by advancing of the downdraft air toward the inflow region.
It extends outward from at or near the mesocyclone center, usually toward the east or southeast, and normally is either nearly stationary or moves northward or northeastward ahead of the mesocyclone.
  More results at FactBites »

 
 

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