Cyclone
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Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the
Weather fronts mark the boundary between two masses of air of different
ahead of the cyclone path. Occluded fronts form late in the cyclone life cycle near the center of the cyclone and often wrap around the storm center.Nomenclature
Structure
There are a number of structural characteristics common to all cyclones. A cyclone is a
Because of the
Formation
Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere.[9] Cyclogenesis is an umbrella term for several different processes that all result in the development of some sort of cyclone.[24] It can occur at various scales, from the microscale to the synoptic scale.
Extratropical cyclones begin as waves along
Tropical cyclones form as a result of significant convective activity, and are warm core.[11] Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.[13] Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear.[14] Cyclolysis is the opposite of cyclogenesis, and is the high-pressure system equivalent, which deals with the formation of high-pressure areas—Anticyclogenesis.[25]
A surface low can form in a variety of ways. Topography can create a surface low.
Tropical cyclogenesis is the development and strengthening of a tropical cyclone.[29] The mechanisms by which tropical cyclogenesis occurs are distinctly different from those that produce mid-latitude cyclones. Tropical cyclogenesis, the development of a warm-core cyclone, begins with significant convection in a favorable atmospheric environment. There are six main requirements for tropical cyclogenesis:
- sufficiently warm sea surface temperatures,[30]
- atmospheric instability,
- high humidity in the lower to middle levels of the troposphere
- enough Coriolis force to develop a low-pressure center
- a preexisting low-level focus or disturbance
- low vertical wind shear.[31]
An average of 86 tropical cyclones of tropical storm intensity form annually worldwide,
Synoptic scale
The following types of cyclones are identifiable in synoptic charts.
Surface-based types
There are three main types of surface-based cyclones: Extratropical cyclones, Subtropical cyclones and Tropical cyclones
Extratropical cyclone
An extratropical cyclone is a
"
Although extratropical cyclones are almost always classified as
Polar low
A polar low is a small-scale, short-lived atmospheric low-pressure system (depression) that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. Polar lows were first identified on the meteorological satellite imagery that became available in the 1960s, which revealed many small-scale cloud vortices at high latitudes. The most active polar lows are found over certain ice-free maritime areas in or near the Arctic during the winter, such as the Norwegian Sea, Barents Sea, Labrador Sea and Gulf of Alaska. Polar lows dissipate rapidly when they make landfall. Antarctic systems tend to be weaker than their northern counterparts since the air-sea temperature differences around the continent are generally smaller [citation needed]. However, vigorous polar lows can be found over the Southern Ocean. During winter, when cold-core lows with temperatures in the mid-levels of the troposphere reach −45 °C (−49 °F) move over open waters, deep convection forms, which allows polar low development to become possible.[39] The systems usually have a horizontal length scale of less than 1,000 kilometres (620 mi) and exist for no more than a couple of days. They are part of the larger class of mesoscale weather systems. Polar lows can be difficult to detect using conventional weather reports and are a hazard to high-latitude operations, such as shipping and gas and oil platforms. Polar lows have been referred to by many other terms, such as polar mesoscale vortex, Arctic hurricane, Arctic low, and cold air depression. Today the term is usually reserved for the more vigorous systems that have near-surface winds of at least 17 m/s.[40]
Subtropical
A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form between the equator and the 50th parallel.[41] As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical cyclones or extratropical cyclones, and used terms such as quasi-tropical and semi-tropical to describe the cyclone hybrids.[42] By 1972, the National Hurricane Center officially recognized this cyclone category.[43] Subtropical cyclones began to receive names off the official tropical cyclone list in the Atlantic Basin in 2002.[41] They have broad wind patterns with maximum sustained winds located farther from the center than typical tropical cyclones, and exist in areas of weak to moderate temperature gradient.[41]
Since they form from extratropical cyclones, which have colder temperatures aloft than normally found in the tropics, the sea surface temperatures required is around 23 degrees Celsius (73 °F) for their formation, which is three degrees Celsius (5 °F) lower than for tropical cyclones.[44] This means that subtropical cyclones are more likely to form outside the traditional bounds of the hurricane season. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm.[45]
Tropical
A tropical cyclone is a
The term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in
While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and a damaging
Many tropical cyclones develop when the atmospheric conditions around a weak disturbance in the atmosphere are favorable.[47] Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an eye. On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses.[11] A tropical cyclone is usually not considered to become subtropical during its extratropical transition.[52]
Upper level types
Polar cyclone
A polar, sub-polar, or Arctic cyclone (also known as a
TUTT cell
Under specific circumstances, upper level cold lows can break off from the base of the tropical upper tropospheric trough (TUTT), which is located mid-ocean in the Northern Hemisphere during the summer months. These upper tropospheric cyclonic vortices, also known as TUTT cells or TUTT lows, usually move slowly from east-northeast to west-southwest, and their bases generally do not extend below 20,000 feet (6,100 m) in altitude. A weak inverted surface trough within the
Mesoscale
The following types of cyclones are not identifiable in synoptic charts.
Mesocyclone
A mesocyclone is a vortex of air, 2.0 kilometres (1.2 mi) to 10 kilometres (6.2 mi) in diameter (the mesoscale of meteorology), within a convective storm.[60] Air rises and rotates around a vertical axis, usually in the same direction as low-pressure systems[61] in both northern and southern hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a supercell.[61][62] Such storms can feature strong surface winds and severe hail.[61] Mesocyclones often occur together with updrafts in supercells, where tornadoes may form.[61] About 1,700 mesocyclones form annually across the United States, but only half produce tornadoes.[13]
Tornado
A tornado is a violently rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or,[63] in rare cases, the base of a cumulus cloud. Also referred to as twisters, a colloquial term in America, or cyclones, although the word cyclone is used in meteorology, in a wider sense, to name any closed low-pressure circulation.
Dust devil
A dust devil is a strong, well-formed, and relatively long-lived whirlwind,[64] ranging from small (half a metre wide and a few metres tall) to large (more than 10 metres wide and more than 1000 metres tall).[64] The primary vertical motion is upward.[64] Dust devils are usually harmless, but can on rare occasions grow large enough to pose a threat to both people and property.[64]
Waterspout
A waterspout is a columnar vortex forming over water that is, in its most common form, a non-
Steam devil
A gentle vortex over calm water or wet land made visible by rising water vapour.
Fire whirl
A fire whirl – also colloquially known as a fire devil, fire tornado, firenado, or fire twister – is a whirlwind induced by a fire and often made up of flame or ash.
Other planets
Cyclones are not unique to Earth. Cyclonic storms are common on Jovian planets, such as the Small Dark Spot on Neptune.[65] It is about one third the diameter of the Great Dark Spot and received the nickname "Wizard's Eye" because it looks like an eye. This appearance is caused by a white cloud in the middle of the Wizard's Eye.[8] Mars has also exhibited cyclonic storms.[7] Jovian storms like the Great Red Spot are usually mistakenly named as giant hurricanes or cyclonic storms. However, this is inaccurate, as the Great Red Spot is, in fact, the inverse phenomenon, an anticyclone.[66]
See also
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