A supercell is a severe thunderstorm with a deep, continuously rotating updraft (a mesocyclone). An updraft or downdraft ( air pocket) is the vertical movement of Air as a Weather related phenomenon A mesocyclone is a Vortex of air approximately 2 to 10 km in diameter (the Mesoscale of meteorology within a convective Storm [1] Of the four classifications of thunderstorms (supercell, single-cell, multi-cell, and squall line), supercells are the largest and most severe
Supercells are usually found isolated from other thunderstorms, although they can sometimes be embedded in a squall line. A squall line is a line of severe thunderstorms that can form along and/or ahead of a Cold front. Because they can last for hours, they are known as quasi-steady-state storms. Supercells have the capability to deviate from the mean wind. If they track to the right of the mean wind (relative to the vertical wind shear), they are said to be "right-movers. " Alternatively, if they track to the left of the mean wind (relative to the shear), they are said to be "left-movers. " Supercells can sometimes develop two separate updrafts with opposing rotations, which splits the storm into two supercells: one left-mover and one right-mover.
Supercells can be any size, large or small, low or high topped. They usually produce copious amounts of hail, torrential rainfall, strong winds, and substantial downbursts. Hail is a form of precipitation which consists of balls or irregular lumps of ice (hailstones Rain is Liquid precipitation. On Earth it is the condensation of atmospheric Water vapor into drops heavy enough to fall often making it to Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) Downburst damagejpg|thumb|right|300px|Downburst damages in a straight line Supercells are one of the few types of clouds that typically spawn tornadoes within the mesocyclone, although only 30% or less do so. A tornado is a violent rotating column of air which is in contact with both the surface of the earth and a Cumulonimbus cloud or in rare cases the base of a Cumulus [2]
Supercells can occur anywhere in the world under the right pre-existing weather conditions. According to some, the first storm to be identified as such was the Wokingham storm over England, which was studied by Keith Browning and Frank Ludlam in 1962. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Keith Browning is a British Meteorologist who worked at Imperial College London, the Met Office and University of Reading department of meteorology [3] As with tornadoes in general, they are most frequent in the Great Plains of the United States. The Great Plains are the broad expanse of Prairie and Steppe which lie east of the Rocky Mountains in the United States and Canada The United States of America —commonly referred to as the
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Anatomy of a supercell
The current conceptual model of a supercell was described in Severe Thunderstorm Evolution and Mesocyclone Structure as Related to Tornadogenesis by Leslie R. Lemon and Charles A. Doswell III. (See Lemon technique). The Lemon technique is a method used by weather radar operators to determine the relative strength of Thunderstorm cells in a vertically sheared environment
Supercells derive their rotation through tilting of horizontal vorticity (an invisible horizontal vortex) caused by wind shear. Vorticity is a mathematical concept used in Fluid dynamics. It can be related to the amount of " circulation " or "rotation" (or more strictly the V erification of the O rigins of R otation in T ornadoes Ex periment or VORTEX, is a field project that seeks to understand how a Wind shear, sometimes referred to as windshear or Wind gradient, is a difference in Wind speed and direction over a relatively Strong updrafts lift the air turning about a horizontal axis and cause this air to turn about a vertical axis. This forms the deep rotating updraft, the mesocyclone. A mesocyclone is a Vortex of air approximately 2 to 10 km in diameter (the Mesoscale of meteorology within a convective Storm
A cap or capping inversion is usually required to form a downdraft of sufficient strength. A capping inversion is an elevated Inversion layer that caps a convective boundary layer. The cap puts an inverted (warm-above-cold) layer above a normal (cold-above-warm) boundary layer, and by preventing warm surface air from sinking too far, allows one or both of the following:
- Air below the cap warms and/or becomes more moist
- Air above the cap cools
This creates a warmer, moister layer below a cooler layer, which is increasingly unstable (because warm air is less dense and tends to rise). In Physics and Fluid mechanics, a boundary layer is that layer of Fluid in the immediate vicinity of a bounding surface When the cap weakens or moves, explosive development follows.
In North America, supercells usually show up on Doppler radar as starting at a point or hook shape on the southwestern side, fanning out to the northeast. The heaviest precipitation is usually on the southwest side, ending abruptly short of the rain-free updraft base or main updraft (not visible to radar). The rear flank downdraft, or RFD, carries precipitation counterclockwise around the north and northwest side of the updraft base, producing a "hook echo" that indicates the presence of a mesocyclone. The rear flank downdraft or RFD is a region of dry air wrapping around the back of a Mesocyclone in a Supercell thunderstorm The hook echo is one of the classical hallmarks of Tornado -producing Supercell Thunderstorms as seen on Weather radar.
Features of a supercell
- Overshooting top
This "dome" feature appears above the anvil of the storm. It is a result of the powerful updraft. If too close it cannot be seen from the ground.
- Precipitation-free base
This area, typically on the southern side of the storm in North America, is relatively precipitation free. This is located beneath the main updraft, and is the main area of inflow. While no precipitation may be visible to an observer, large hail and rain may be falling from this area. It is more accurately called the main updraft area.
- Wall cloud
The wall cloud forms near the downdraft/updraft interface. A wall cloud, or pedestal cloud, is a Cloud formation associated with Thunderstorms It is a marked lowering typically beneath the rain-free base (RFB This "interface" is the area between the precipitation area and the precipitation-free base. Wall clouds form when rain-cooled air from the downdraft is pulled into the updraft. This wet, cold air quickly saturates as it is lifted by the updraft, forming a cloud that seems to "descend" from the precipitation-free base. Wall clouds are common and are not exclusive to supercells: Only a few actually produce a tornado. Wall clouds that persist for more than ten minutes, wall clouds that seem to move violently up or down, and violent movements of cloud fragments (scud or fractus) near the wall cloud are indications that a tornado could form.
- Mammatus clouds
Mammatus (Mamma, Mammatocumulus) are bulbous or pillow-like cloud formations extending from beneath the anvil of a thunderstorm. Mammatus (also known as mammatocumulus meaning "bumpy clouds" is a meteorological term applied to a cellular pattern of pouches hanging underneath the These clouds form as cold air in the anvil region of a storm sinks into warmer air beneath it. Mammatus are most apparent when they are lit from one side or below and are therefore at their most impressive near sunset or shortly after sunrise when the sun is low in the sky. Mammatus are not exclusive to supercells and can be associated with developed thunderstorms and cumulonimbus.
- Precipitation area
This is the area of heaviest precipitation. Between the precipitation-free base and the precipitation area, a "vaulted" or "cathedral" feature can be observed. In high precipitation supercells an area of heavy precipitation may occur beneath the main updraft area.
- Flanking line
A line of smaller cumulonimbi or cumulus that form in the warm rising air pulled in by the main updraft. Cumulonimbus (Cb is a type of Cloud that is tall dense and involved in Thunderstorms and other intense Weather.
Radar features of a supercell
- Hook echo or Pendant
The "hook echo" is the area of confluence between the main updraft and the rear flank downdraft (RFD). The hook echo is one of the classical hallmarks of Tornado -producing Supercell Thunderstorms as seen on Weather radar. This indicates the position of the mesocyclone, and likely a tornado.
- Bounded weak echo region (or BWER)
This is a region of low radar reflectivity bounded above by an area of higher radar reflectivity. The bounded weak echo region, also known as a BWER or a vault is a radar signature within a Thunderstorm characterized by a local minimum in radar This is evidence of a strong updraft.
- Inflow notch
A "notch" of weak reflectivity on the inflow side of the cell. This is not a V-Notch.
- V Notch
A "V" shaped notch on the leading edge of the cell, opening away from the main downdraft. This is an indication of divergent flow around a powerful updraft.
See also: Radar
Supercell variations
Supercell thunderstorms are sometimes classified by meteorologists and storm spotters into three categories. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Meteorology (from Greek grc μετέωρος metéōros, "high in the sky" and grc -λογία -logia) is the Interdisciplinary SKYWARN is a program of the United States ' National Weather Service (NWS However, not all supercells fit neatly into any one category, and many resemble all three at different times during the lifespan of the storm. The standard definition given above is referred to as the Classic supercell. All types of supercells can produce severe weather.
Low Precipitation (LP)
LP supercells contain a small precipitation (rain/hail) core separate from the updraft. This type of supercell may be easily identifiable with "sculpted" cloud striations in the updraft base or even a "corkscrewed" or "barber pole" appearance on the updraft, and sometimes an almost "anorexic" look compared to classic supercells. This is because they often form along dry lines, thus leaving them with little available moisture despite high upper level wind shear. A dry line, (also called dew point line, or Marfa front) is an important factor in Severe weather frequency in the Great Plains of They usually dissipate rapidly rather than turning into classic or HP supercells, although it is still not unusual for them to do the latter, especially if they happen to collide with a much moister air mass along the way. Although these storms usually produce weak tornadoes, they have been known to produce strong ones. These storms usually produce hail less than 1. 00 inch in diameter [4]but can produce large hail even with little or no visible precipitation core, making them hazardous to storm chasers and people and animals caught outside. Due to the lack of a heavy precipitation core, LP supercells can sometimes show weak radar reflectivity without clear evidence of a hook echo, when in fact they are producing a tornado at the time. The hook echo is one of the classical hallmarks of Tornado -producing Supercell Thunderstorms as seen on Weather radar. This is where observations by storm spotter and storm chasers may be of vital importance. SKYWARN is a program of the United States ' National Weather Service (NWS Funnel clouds, or more rarely, weak tornadoes will sometimes form midway between the base and the top of the storm, descending from the main Cb (cumulonimbus) cloud. A funnel cloud is a Funnel -shaped Cloud of condensed Water droplets associated with a rotating column of air and extending from the base of A tornado is a violent rotating column of air which is in contact with both the surface of the earth and a Cumulonimbus cloud or in rare cases the base of a Cumulus Cumulonimbus (Cb is a type of Cloud that is tall dense and involved in Thunderstorms and other intense Weather. Lightning is rare compared to other supercell types, but it is not unknown and is more likely to occur as intracloud lightning rather than cloud-to-ground lightning. In North America, these storms almost exclusively form from the Rocky Mountains to the Mississippi River in the spring and summer months. Mountain peaks of the Rocky Mountains The Rocky Mountains, often called the Rockies, are a Mountain range in western North America. The Mississippi River is the second longest River in the United States, with a length of from its source in Lake Itasca in Minnesota to They can occur as far north as Montana, North Dakota and even in the provinces of Alberta and Saskatchewan in Canada. Montana ( is a state in the Western United States. One-third of the state in the western part contains numerous mountain ranges (approximately 77 named of the northern North Dakota ( is a state located in the Midwestern and Western regions of the United States of America. Alberta (ælˈbɝtə is one of Canada's prairie provinces. It became a province on September 1 1905 Saskatchewan (səˈskætʃəwən) is a prairie province in Canada, which has an area of 588276 Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page They have also been observed by storm chasers in Australia. For a topic outline on this subject see List of basic Australia topics.
LP supercells are quite sought after by storm chasers, because the limited amount of precipitation makes sighting tornadoes at a safe distance much less difficult than with a Classic or HP supercell.
High Precipitation (HP)
The HP supercell has a much heavier precipitation core that actually can wrap all the way around the mesocyclone. These are especially dangerous storms, since the mesocyclone is wrapped with rain and can hide the tornado from view. These storms also cause flooding due to heavy rain, damaging downbursts and weak tornadoes, although they are also known to produce strong to violent tornadoes. Downburst damagejpg|thumb|right|300px|Downburst damages in a straight line They have a lower potential for damaging hail than Classic and LP supercells, although damaging hail is possible. It has been observed by some spotters that they tend to produce more cloud-to-ground and intracloud lightning than the other types. Also, unlike the LP and Classic types, severe events usually occur at the front (southeast) of the storm. The HP supercell is the most common type of supercell in the United States east of the Mississippi River and in the southern parts of the provinces of Ontario and Quebec in Canada. The United States of America —commonly referred to as the The Mississippi River is the second longest River in the United States, with a length of from its source in Lake Itasca in Minnesota to Ontario (ɒnˈtɛrioʊ is a province located in the central part of Canada, the largest by population and second largest after Quebec Quebec (kwɨˈbɛk Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page
Severe weather
Supercells can produce:
Severe events associated with a supercell almost always occur in the area of the updraft/downdraft interface. A tornado is a violent rotating column of air which is in contact with both the surface of the earth and a Cumulonimbus cloud or in rare cases the base of a Cumulus Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or In the Northern Hemisphere, this is most often the rear flank (southwest side) of the precipitation area in LP and classic supercells, but sometimes the leading edge (southeast side) of HP supercells. Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball'
While tornadoes are perhaps the most dramatic of these severe events, all are dangerous. High winds caused by powerful outflow can reach over 148 km/h (92 mph)[5][6] and downbursts can cause tornado-like damage. Downburst damagejpg|thumb|right|300px|Downburst damages in a straight line Flooding is the leading cause of death associated with severe weather. [7]
Note that none of these severe events are exclusive to supercells, although these events are highly predictable once a supercell has formed.
Some reports also suggest that the deluge on 26 July 2005 in Mumbai, India was caused by a supercell when there was a cloud formation 15km (9. Overview Thousands of schoolchildren were stranded due to flooding and could not reach home for up to 18 hours Events 657 - Battle of Siffin. 811 - Battle of Pliska; Byzantine Emperor Nicephorus Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Mumbai ( Marathi:,, IPA: formerly Bombay, is the capital of the Indian state of Maharashtra and the financial 32 miles) high over the city. On this day 944mm (37. 16 inches) of rain fell over the city, of which 700mm (27. 56 inches) fell in just four hours.
Notes
References
- Structure and Dynamics of Supercell Thunderstorms - NWS
- University of Illinois World Weather Project
- Weather Glossary for Storm Spotters - NWS
- Lemon, Leslie R. (1998): On the Mesocyclone "Dry Intrusion" and Tornadogenesis
- Lemon, Leslie R. , Charles A. Doswell III (1979): "Severe Thunderstorm Evolution and Mesocyclone Structure as Related to Tornadogenesis". Monthly Weather Review Vol. 107, No. 9, pp. 1184-1197.
- Browning, K. A. and Ludlam, F. H. (1962): "Airflow In Convective Storms", Quarterly Journal of the Royal Meteorological Society 88, 117-135. (PDF)
External links
- Electronic Journal of Severe Storms Meteorology
- Explanation of Supercells
- Picture sequence of a supercell in Nebraska
- Slideshow of Supercell images
Dictionary
supercell
-noun
- A severe thunderstorm with updrafts and downdrafts that are in near balance, allowing the storm to maintain itself for several hours. Supercells often produce large hail, powerful downpours, very strong winds and sometimes tornadoes.
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