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An extratropical cyclone near Iceland
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In meteorology, a cyclone (/ˈsaɪ.kloʊn/) is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above (opposite to an anticyclone).[1][2] Cyclones are characterized by inward-spiraling winds that rotate about a zone of low pressure.[3][4]

Cyclones have also been seen on planets other than the Earth, such as Mars, Jupiter, and Neptune.[5][6] Cyclogenesis is the process of cyclone formation and intensification.[7]

Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.

Weather fronts mark the boundary between two masses of air of different temperature, humidity, and densities, and are associated with the most prominent meteorological phenomena. Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines or dry lines. Such fronts form west of the circulation center and generally move from west to east; warm fronts form east of the cyclone center and are usually preceded by stratiform precipitation and fog. Warm fronts move poleward 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.

Tropical cyclogenesis describes the process of development of tropical cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core.[8][9] Cyclones can transition between extratropical, subtropical, and tropical phases.[10] Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.[11] Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear.[12] In the Atlantic and the northeastern Pacific oceans, a tropical cyclone is generally referred to as a hurricane (from the name of the ancient Central American deity of wind, Huracan), in the Indian and south Pacific oceans it is called a cyclone, and in the northwestern Pacific it is called a typhoon.[13] The growth of instability in the vortices is not universal. For example, the size, intensity, moist-convection, surface evaporation, the value of potential temperature at each potential height can affect the nonlinear evolution of a vortex.[14]

Name

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The term cyclone comes from the Greek word κύκλος (kýklos, meaning "circle" or "ring" in Ancient Greek), due to the spiraling nature of a cyclone's winds.[15] The word was coined by Henry Piddington, an official in the British East India Company who published 40 papers dealing with tropical storms from Calcutta between 1836 and 1855 in The Journal of the Asiatic Society.[16]

Structure

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Comparison between extratropical and tropical cyclones on surface analysis

There are a number of structural characteristics common to all cyclones. A cyclone is a low-pressure area.[17] A cyclone's center (often known in a mature tropical cyclone as the eye), is the area of lowest atmospheric pressure in the region.[17] Near the center, the pressure gradient force (from the pressure in the center of the cyclone compared to the pressure outside the cyclone) and the force from the Coriolis effect must be in an approximate balance, or the cyclone would collapse on itself as a result of the difference in pressure.[18]

Because of the Coriolis effect, the wind flow around a large cyclone is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.[19] In the Northern Hemisphere, the fastest winds relative to the surface of the Earth therefore occur on the eastern side of a northward-moving cyclone and on the northern side of a westward-moving one; the opposite occurs in the Southern Hemisphere.[20]

Formation

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The initial extratropical low-pressure area forms at the location of the red dot on the image. It is usually perpendicular (at a right angle to) the leaf-like cloud formation seen on satellite during the early stage of cyclogenesis. The location of the axis of the upper level jet stream is in light blue.
Tropical cyclones form when the energy released by the condensation of moisture in rising air causes a positive feedback loop over warm ocean waters.[21]
Main articles: Cyclogenesis and Tropical cyclogenesis

Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere.[7] Cyclogenesis is an umbrella term for several different processes that all result in the development of some sort of cyclone.[22]

Tropical cyclones form as a result of significant convective activity, and are warm core.[9] Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.[11] Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear.[12] Cyclolysis is the opposite of cyclogenesis, and is the high-pressure system equivalent, which deals with the formation of high-pressure areas—anticyclogenesis.[23]

A surface low can form in a variety of ways. Topography can create a surface low. Mesoscale convective systems can spawn surface lows that are initially warm-core.[24] The disturbance can grow into a wave-like formation along the front and the low is positioned at the crest. Around the low, the flow becomes cyclonic. This rotational flow moves polar air towards the equator on the west side of the low, while warm air move towards the pole on the east side. A cold front appears on the west side, while a warm front forms on the east side. Usually, the cold front moves at a quicker pace than the warm front and "catches up" with it due to the slow erosion of higher density air mass out ahead of the cyclone. In addition, the higher density air mass sweeping in behind the cyclone strengthens the higher pressure, denser cold air mass. The cold front over takes the warm front, and reduces the length of the warm front.[25] At this point an occluded front forms where the warm air mass is pushed upwards into a trough of warm air aloft, which is also known as a trowal.[26]

Tropical cyclogenesis is the development and strengthening of a tropical cyclone.[27] 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 two main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures,[28] and low vertical wind shear.[29]

An average of 86 tropical cyclones of tropical storm intensity form annually worldwide,[30] with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones (at least Category 3 intensity on the Saffir–Simpson hurricane scale).[31]

Synoptic types

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A fictitious synoptic chart of an extratropical cyclone affecting the UK and Ireland. The blue arrows between isobars indicate the direction of the wind, while the "L" symbol denotes the centre of the "low". Note the occluded, cold and warm frontal boundaries.

The following types of cyclones are identifiable in synoptic charts.[32]

Surface-based types

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See also: Low-pressure area

There are three main types of surface-based cyclones: extratropical cyclones, subtropical cyclones and tropical cyclones.

Extratropical cyclone

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Main article: Extratropical cyclone

An extratropical cyclone is a synoptic scale low-pressure weather system that does not have tropical characteristics,[33] as it is connected with fronts and horizontal gradients (rather than vertical) in temperature and dew point otherwise known as "baroclinic zones".[34]

"Extratropical" is applied to cyclones outside the tropics, in the middle latitudes. These systems may also be described as "mid-latitude cyclones" due to their area of formation, or "post-tropical cyclones" when a tropical cyclone has moved (extratropical transition) beyond the tropics.[34][35] They are often described as "depressions" or "lows" by weather forecasters and the general public.[36] These are the everyday phenomena that, along with anticyclones, drive weather over much of the Earth.[37]

Although extratropical cyclones are almost always classified as baroclinic since they form along zones of temperature and dewpoint gradient within the westerlies, they can sometimes become barotropic late in their life cycle when the temperature distribution around the cyclone becomes fairly uniform with radius.[38] An extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone, if it dwells over warm waters sufficient to warm its core, and as a result develops central convection.[39] A particularly intense type of extratropical cyclone that strikes during winter is known colloquially as a nor'easter.[40]

Polar low

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Main article: Polar low
A polar low over the Sea of Japan in December 2009

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. However, vigorous polar lows can be found over the Southern Ocean.[41]

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.[42] 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 (38 mph; 61 km/h).[43]

Subtropical

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Subtropical Storm Alex in the north Atlantic Ocean in January 2016
Main article: Subtropical cyclone

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.[44] 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.[45] By 1972, the National Hurricane Center in the United States officially recognized this cyclone category.[46] Subtropical cyclones began to receive names off the official tropical cyclone list in the Atlantic Basin in 2002.[44] 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.[44]

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.[47] 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.[48]

Tropical

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Main article: Tropical cyclone
Hurricane Florence viewed from the International Space Station

A tropical cyclone is a storm system characterized by a low-pressure center and numerous thunderstorms that produce strong winds and flooding rain.[49] A tropical cyclone feeds on heat released when moist air rises, resulting in condensation of water vapour contained in the moist air.[49] They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems.[49][9]

The term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in tropical regions of the globe,[50] and their dependence on Maritime Tropical air masses for their formation. The term "cyclone" refers to the storms' cyclonic nature, with counterclockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere.[50] Depending on their location and strength, tropical cyclones are referred to by other names, such as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply as a cyclone.[50]

While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and a damaging storm surge.[51] Their winds increase the wave size, and in so doing they draw more heat and moisture into their system, thereby increasing their strength. They develop over large bodies of warm water,[52] and hence lose their strength if they move over land.[53] This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from strong winds.[50] Heavy rains, however, can produce significant flooding inland.[50] Storm surges are rises in sea level caused by the reduced pressure of the core that in effect "sucks" the water upward and from winds that in effect "pile" the water up. Storm surges can produce extensive coastal flooding up to 40 kilometres (25 mi) from the coastline.[50] Although their effects on human populations can be devastating, tropical cyclones can also relieve drought conditions.[54] They also carry heat and energy away from the tropics and transport it toward temperate latitudes,[50] which makes them an important part of the global atmospheric circulation mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere.[50]

Many tropical cyclones develop when the atmospheric conditions around a weak disturbance in the atmosphere are favorable.[50] 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.[9] A tropical cyclone is usually not considered to become subtropical during its extratropical transition.[55]

Upper level types

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Polar cyclone

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Main article: Polar cyclone

A polar, sub-polar, or Arctic cyclone (also known as a polar vortex)[56] is a vast area of low pressure that strengthens in the winter and weakens in the summer.[57] A polar cyclone is a low-pressure weather system, usually spanning 1,000 kilometres (620 mi) to 2,000 kilometres (1,200 mi),[58] in which the air circulates in a counterclockwise direction in the northern hemisphere, and a clockwise direction in the southern hemisphere. The Coriolis acceleration acting on the air masses moving poleward at high altitude, causes a counterclockwise circulation at high altitude. The poleward movement of air originates from the air circulation of the Polar cell. The polar low is not driven by convection as are tropical cyclones, nor the cold and warm air mass interactions as are extratropical cyclones, but is an artifact of the global air movement of the Polar cell. The base of the polar low is in the mid to upper troposphere. In the Northern Hemisphere, the polar cyclone has two centers on average. One center lies near Baffin Island and the other over northeast Siberia.[56] In the southern hemisphere, it tends to be located near the edge of the Ross ice shelf near 160 west longitude.[59] When the polar vortex is strong, its effect can be felt at the surface as a westerly wind (toward the east). When the polar cyclone is weak, significant cold outbreaks occur.[60]

TUTT cell

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Main article: Upper tropospheric cyclonic vortex

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 trade wind is generally found underneath them, and they may also be associated with broad areas of high-level clouds. Downward development results in an increase of cumulus clouds and the appearance of a surface vortex. In rare cases, they become warm-core tropical cyclones. Upper cyclones and the upper troughs that trail tropical cyclones can cause additional outflow channels and aid in their intensification. Developing tropical disturbances can help create or deepen upper troughs or upper lows in their wake due to the outflow jet emanating from the developing tropical disturbance/cyclone.[61][62]

Non-synoptic types

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The following types of cyclones are not identifiable in synoptic charts.[32]

Mesocyclone

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Main article: 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.[63] Air rises and rotates around a vertical axis, usually in the same direction as low-pressure systems[64] in both northern and southern hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a supercell.[64][65] Such storms can feature strong surface winds and severe hail.[64] Mesocyclones often occur together with updrafts in supercells, where tornadoes may form.[64] About 1,700 mesocyclones form annually across the United States, but only half produce tornadoes.[11]

Dust devil

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Main article: Dust devil

A dust devil is a type of vortex that involves debris such as dust being lifted upward into the air.[66][67] Most dust devils are between 10 ft (3.0 m) and 300 ft (91 m) wide, and between 500 ft (150 m) and 1,000 ft (300 m) tall, although the strongest can be several thousand feet tall. Wind speed varies depending on the size of the dust devil; larger ones have winds of at least 60 mph (97 km/h), reaching up to 75 mph (121 km/h). Dust devils form from a warm surface during sunny days, often in an area where surface types change, and require the surrounding air to be unstable, dissipating when conditions become more stable; they therefore often from in deserts. They usually dissipate after only a few minutes, but stronger dust devils can last over an hour. Dust devils are smaller than tornadoes and are usually harmless, though stronger ones can destroy small structures. Dust devils have been found on Mars as well as on Earth.[66]

Waterspout

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Main article: Waterspout

A waterspout is a columnar vortex forming over water that is, in its most common form, a non-supercell tornado over water that is connected to a cumuliform cloud. While it is often weaker than most of its land counterparts, stronger versions spawned by mesocyclones do occur.[68]

Steam devil

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Main article: Steam devil

A steam devil is a gentle vortex over calm water or wet land that is made visible by rising water vapour.[69]

Fire whirl

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Main article: 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

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Main article: Extraterrestrial vortex
Cyclone on Mars, imaged by the Hubble Space Telescope

Cyclones are not unique to Earth. Cyclonic storms are common on giant planets, such as the Small Dark Spot on Neptune.[70] 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.[6] Mars has also exhibited cyclonic storms.[5] 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.[71]

See also

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References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Cyclone

View on Grokipedia
from Grokipedia
In , a cyclone is a large-scale that rotates around a strong center of low , distinct from a high-pressure anticyclone. Cyclones are characterized by inward-spiraling winds that rotate counterclockwise in the and clockwise in the due to the Coriolis effect. They can form over land or ocean and vary in scale from synoptic systems affecting entire continents to mesoscale vortices like tornadoes. Major types include extratropical cyclones (common in mid-latitudes and associated with fronts and weather fronts), tropical cyclones (intense storms over warm oceans), subtropical cyclones, polar lows, upper-level cyclones, and smaller-scale phenomena such as mesocyclones and dust devils, as detailed in subsequent sections. Extraterrestrial cyclones also occur on other . Tropical cyclones, a prominent subtype, are rotating, organized systems of clouds and thunderstorms that originate over tropical or subtropical waters and have a closed low-level circulation around a center of low pressure. Known regionally as a hurricane in the North Atlantic, Northeast Pacific, and central North Pacific, a in the Northwest Pacific, or simply a severe tropical cyclone in the South Pacific and , these storms are fueled by the release of heat from warm ocean surfaces and can produce destructive winds exceeding 74 miles per hour (119 km/h), heavy rainfall, and storm surges. Tropical cyclones typically form from a pre-existing near-surface disturbance, such as an easterly wave or low-pressure trough, when conditions include sea surface temperatures of at least 80°F (27°C) to a depth of about 150 feet (46 m), a moist mid-level atmosphere, an environment that cools rapidly with height to promote instability, low vertical of less than 23 mph (37 km/h), and a at least 300 miles (480 km) from the . These systems develop through stages of intensification: starting as a tropical depression with winds under 39 mph (63 km/h), progressing to a tropical storm at 39–73 mph (63–118 km/h), and reaching hurricane or strength at 74 mph (119 km/h) or higher, with further categorization into categories 1 through 5 based on the Saffir-Simpson Hurricane Wind Scale for escalating wind speeds and potential damage. Structurally, a mature features a calm, sinking eye at its center—typically 20–40 miles (32–64 km) wide with light winds—surrounded by the eyewall, a ring of intense thunderstorms where the strongest winds occur, and extending outward are spiral rainbands that deliver additional heavy precipitation, gusts, and occasional tornadoes. Air spirals inward toward the low-pressure center in a counterclockwise direction in the or clockwise in the , rising through before exiting at upper levels. These storms occur globally across seven major basins, with distinct seasonal patterns—such as June to in the North Atlantic (peaking in ) and year-round but peaking July to in the Northwest Pacific—and rarely form near the equator due to the Coriolis effect's weakness there.

Terminology and Classification

Nomenclature

A cyclone is defined as a large-scale characterized by a low-pressure center around which air masses rotate, typically counterclockwise in the and clockwise in the , due to the deflection imposed by the Coriolis effect on moving air masses. This rotation arises because causes winds to veer rightward in the and leftward in the , fostering the cyclonic flow around the pressure minimum. The term "cyclone" derives from the Greek word kyklos, meaning "circle" or "," reflecting the spiraling patterns observed in these systems. It was coined in 1848 by British meteorologist Henry Piddington, who introduced it in his work The Sailor's Horn-Book for the Law of Storms to describe rotating storms in the , drawing on roots to emphasize their coiled, circular motion akin to a snake's form. This nomenclature gained prominence in the amid growing meteorological studies of tropical and extratropical storms, particularly in colonial observatories in and , where Piddington and contemporaries like those in of documented storm dynamics. Regionally, the term "cyclone" specifically denotes tropical cyclones in the , South Pacific, and southwestern Pacific basins, while equivalent storms are called "hurricanes" in the North Atlantic and northeastern Pacific, and "typhoons" in the northwestern Pacific. These distinctions stem from historical linguistic influences: "hurricane" traces to the Taino word huracán for a god in the , and "typhoon" likely originates from typhon () via Chinese or roots. In contrast, anticyclones are high-pressure systems with opposite rotation—clockwise in the and counterclockwise in the Southern—where air diverges outward, often leading to clear, stable conditions.

Scale-Based Classification

Cyclones in the atmosphere are classified based on their spatial and temporal scales, which provide a hierarchical framework for distinguishing their dynamics and impacts. The primary criterion for this classification is the Rossby number (Ro), defined as the ratio of inertial forces to Coriolis forces, given by Ro=UfLRo = \frac{U}{fL}, where UU is the characteristic wind speed, ff is the Coriolis parameter, and LL is the horizontal length scale. Small values of Ro (typically << 1) indicate that Earth's rotation dominates, leading to geostrophic balance in large-scale systems, while larger Ro values (approaching or exceeding 1) signify increasing influence of local inertial effects in smaller-scale vortices. This dimensionless parameter helps differentiate rotationally constrained flows from those driven more by local convection or friction. Synoptic-scale cyclones encompass the largest atmospheric vortices, with horizontal length scales of 1000 km or more and temporal scales spanning several days. These systems, including extratropical and tropical cyclones, evolve slowly and are influenced by planetary-scale circulation patterns, often driven by baroclinic instability where horizontal temperature gradients release potential energy into kinetic form. Upper-level cyclones, a subset occurring in the mid-to-upper troposphere, form in association with jet stream dynamics, where divergences ahead of jet streaks promote cyclonic development aloft. Mesoscale cyclones operate on intermediate scales, with length scales ranging from 1 to 1000 km and time scales of hours to about one day. These are frequently convective in origin, arising within organized clusters of thunderstorms known as mesoscale convective systems (MCSs), where mesoscale vorticity develops from interactions between updrafts, downdrafts, and ambient shear. Boundary layer cyclones, confined to the lowest 1-2 km of the atmosphere, include smaller vortices such as gust front circulations or sea breeze fronts, influenced heavily by surface friction and heating. Sub-mesoscale features, with scales below 10 km and time scales of minutes to hours, bridge mesoscale and microscale processes but are less commonly classified as full cyclones due to their transient nature. Beyond the atmosphere, the term "cyclone" broadly applies to rotating vortices in other fluid media for completeness, such as oceanic cyclones (anticyclonic or cyclonic eddies in ocean currents) that mirror atmospheric dynamics but are modulated by density stratification and bathymetry.

General Characteristics

Physical Structure

A cyclone is defined by its central low-pressure area, where atmospheric pressure is minimized, creating a pressure gradient that drives the cyclonic rotation of winds around the system. This low-pressure center serves as the dynamical core, with air spiraling inward and upward due to the convergence of moist air masses. In extratropical cyclones, the low-pressure center is frequently demarcated by warm and cold fronts, where the warm front features advancing warm air overriding cooler air, and the cold front involves denser cold air displacing warmer air, both leading to enhanced uplift and weather activity along these boundaries. Spiral rainbands, consisting of organized convective clouds and precipitation, commonly encircle the low-pressure center in a cyclonic spiral pattern (counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere), transporting moisture and latent heat inward while contributing to the cyclone's overall asymmetry and intensity. In intense tropical cyclones, the low-pressure center develops into a distinct eye—a region of subsidence and relative calm—surrounded by the eyewall, a narrow ring of severe thunderstorms featuring the peak winds and heaviest rainfall. The vertical structure of cyclones exhibits significant variation depending on type, with tropical cyclones characterized by a warm core structure, wherein temperatures are anomalously high relative to the surroundings throughout much of the troposphere, particularly aloft, supporting sustained convection without reliance on baroclinicity. In contrast, extratropical cyclones possess a cold core, with the lowest temperatures concentrated near the center aloft, producing thermal wind shear that allows the system to draw energy from horizontal temperature gradients. Baroclinic cyclones, such as those in mid-latitudes, display a tilt with height, where the upper-level low-pressure center is displaced poleward or eastward from the surface low, facilitating the development of frontal zones and wave propagation. Cyclone wind profiles typically feature maximum tangential winds located near the surface in warm-core systems or at mid-tropospheric levels in baroclinic ones, with speeds decreasing outward in a radial gradient that maintains the system's coherence. These winds approximate a state of gradient wind balance, described by the equation V2r=1ρ∂p∂r−fV,\frac{V^2}{r} = \frac{1}{\rho} \frac{\partial p}{\partial r} - f V, where VV denotes the tangential wind speed, rr the radial distance from the center, ρ\rho the air density, pp the pressure, and ff the Coriolis parameter; this balance equates the centrifugal force to the radial pressure gradient force minus the Coriolis force for cyclonic flow. Asymmetries in cyclone structure and motion arise from the beta effect, the latitudinal variation in planetary vorticity (β = ∂f/∂y), which induces a net transverse flow across the vortex, often resulting in enhanced convection and winds on the forward side relative to the storm's track and a poleward deflection in propagation. Synoptic-scale cyclones tend to exhibit broader radial extents in their pressure and wind fields compared to smaller mesoscale systems.

Formation Processes

Cyclones form through dynamic processes driven primarily by instabilities in the atmosphere that convert potential energy into kinetic energy, leading to organized rotational motion. A key mechanism is baroclinic instability, which arises from horizontal temperature gradients that create vertical wind shear, providing available potential energy for disturbance growth. This instability is quantified by the Eady growth rate, given by the formula σ=0.31f∂V∂z/N\sigma = 0.31 f \frac{\partial V}{\partial z} / N where ff is the Coriolis parameter, ∂V/∂z\partial V / \partial z is the vertical shear of the geostrophic wind, and NN is the Brunt-Väisälä frequency representing static stability. In regions with strong baroclinicity, such as mid-latitudes, these gradients destabilize the flow, allowing wave-like perturbations to amplify into cyclonic systems. Additionally, latent heat release from convective processes plays a crucial role by warming the air aloft, further reducing static stability and enhancing upward motion, which sustains the instability. Earth's rotation is essential for cyclone development through the Coriolis force, which deflects moving air parcels and imparts angular momentum to initial disturbances. Without sufficient Coriolis effect, as near the equator, cyclonic spin-up cannot occur effectively, requiring an initial vorticity source—such as from convergence or pre-existing eddies—to initiate rotation. This deflection leads to the characteristic counterclockwise rotation in the Northern Hemisphere and clockwise in the Southern Hemisphere. Energy for cyclone formation and maintenance varies by type but shares principles of thermodynamic forcing. Synoptic-scale cyclones draw primarily from baroclinic energy released through slantwise convection along frontal boundaries, converting potential energy from meridional temperature contrasts into eddy kinetic energy. In contrast, tropical cyclones rely on ocean heat fluxes, where sea surface temperatures exceeding 26.5°C enable evaporation and subsequent latent heat release, fueling deep convection and self-sustaining intensification. The lifecycle of a cyclone typically progresses through distinct stages: genesis, where initial disturbances organize under favorable conditions; intensification, driven by convergence that increases vorticity and pressure gradients; maturity, when peak intensity is reached and the system becomes most organized; and decay, resulting from surface friction, reduced energy supply, or landfall that disrupts the moisture and heat sources.

Synoptic-Scale Cyclones

Extratropical Cyclones

Extratropical cyclones, also known as mid-latitude cyclones, are large-scale low-pressure systems driven by baroclinic instability, where horizontal temperature contrasts between polar and subtropical air masses generate potential energy for storm development. These systems typically form in the westerlies between 30° and 70° latitude and are closely associated with the polar jet stream, which enhances their growth through upper-level divergence. They feature distinct frontal boundaries—warm fronts advancing into cooler air, cold fronts displacing warmer air, and occluded fronts where the two converge—creating sharp contrasts in temperature, moisture, and wind. On satellite imagery, mature extratropical cyclones often display characteristic comma-shaped cloud patterns, with the "head" representing the warm sector and the "tail" the cold front, spanning diameters of approximately 1,500 to 5,000 km. These storms are most prevalent during the winter season in each hemisphere, when stronger baroclinicity and reduced solar heating amplify temperature gradients, leading to more frequent and intense . The formation of extratropical cyclones follows conceptual models that describe their lifecycle, including the classic Norwegian cyclone model and the Shapiro-Keyser model. The Norwegian model, developed in the early 20th century, outlines progression from an initial frontal wave along a baroclinic zone to a mature stage with deepening low pressure, followed by occlusion as the cold front overtakes the warm front, eventually leading to dissipation. In contrast, the Shapiro-Keyser model, identified through numerical simulations of explosive cyclones, emphasizes a "warm seclusion" process where the warm conveyor belt—a broad ascending airstream of moist air rising from the surface to the mid-troposphere ahead of the cold front—wraps around the cyclone center, isolating a pocket of warm air at low levels while the system deepens rapidly. Accompanying this is the dry intrusion, a descending airstream of dry air from the upper troposphere behind the cold front, which enhances subsidence and clear skies in the rear sector, further fueling baroclinic development through latent heat release in the warm conveyor belt. Notable examples include bomb cyclones in the North Atlantic, defined as extratropical systems undergoing explosive cyclogenesis with central pressure drops of at least 24 hPa over 24 hours (or 1 hPa per hour at mid-latitudes), which can produce severe winds and coastal flooding; these events are particularly common along the U.S. East Coast and western Europe during winter. The 1987 Great Storm, an intense extratropical cyclone that struck the British Isles and northwestern France on October 15–16, exemplifies such windstorms, with gusts exceeding 100 mph (160 km/h), causing 18 fatalities and widespread damage from fallen trees and power outages. More recently, the November 2024 Northeast Pacific bomb cyclone struck the U.S. West Coast and Canada on November 19, producing hurricane-force winds, at least two deaths, and power outages affecting over 600,000 customers due to downed lines spanning more than 500 miles. Climatologically, extratropical cyclones dominate winter weather in the mid-latitudes, accounting for 60–70% of annual precipitation in regions like Europe and eastern North America through associated frontal rainfall and embedded convection. Recent studies from the 2020s link their intensification to Arctic amplification—the faster warming of the Arctic compared to lower latitudes—which reduces meridional temperature gradients but increases atmospheric moisture and instability, leading to 10–20% stronger cyclone intensities in some Northern Hemisphere sectors, as evidenced by analyses of reanalysis data and climate models showing enhanced precipitation extremes and wind speeds.

Tropical Cyclones

Tropical cyclones, also known as hurricanes or typhoons depending on the region, are intense, warm-core low-pressure systems that develop over tropical or subtropical ocean waters, characterized by organized convection and a closed surface wind circulation without associated fronts. These storms derive their energy primarily from the latent heat released by condensation of moist air, leading to sustained winds exceeding 119 km/h (74 mph) and often causing significant coastal flooding, high winds, and heavy rainfall upon landfall. Unlike extratropical cyclones, tropical cyclones exhibit a symmetric structure driven by ocean-atmosphere interactions rather than baroclinic instability. Formation of tropical cyclones requires specific environmental conditions, including sea surface temperatures (SSTs) warmer than 26.5°C to a depth of at least 50 meters, which provide the necessary heat and moisture. High atmospheric moisture in the lower troposphere is essential to sustain deep convection, while low vertical wind shear—typically below 10 m/s—prevents the disruption of the storm's vertical structure. Additionally, the system must form at least 5° latitude from the equator to experience sufficient Coriolis force, with the parameter exceeding approximately 10^{-5} s^{-1}, enabling cyclonic rotation. Once initiated, intensification often occurs through mechanisms such as conditional instability of the second kind (CISK), where cumulus convection cooperatively enhances large-scale organization, or wind-induced surface heat exchange (WISHE), in which increasing surface winds boost evaporation and sea spray, amplifying heat and moisture fluxes into the boundary layer. These feedbacks can lead to rapid strengthening, particularly under favorable conditions like high SSTs and minimal shear. The physical structure of a mature tropical cyclone features a central calm region known as the eye, typically 10-50 km in diameter, surrounded by the eyewall—a ring of intense thunderstorms where maximum winds occur. Spiral rainbands extend outward, feeding moisture into the system, while the overall warm-core nature results in a pressure minimum at the center, often dropping below 950 hPa in intense storms. Eyewall replacement cycles (ERCs) are a common dynamic process in major tropical cyclones, where a secondary eyewall forms outside the primary one, leading to temporary weakening as the inner eyewall dissipates before the outer structure contracts and intensifies the storm. Intensity is classified using the Saffir-Simpson Hurricane Wind Scale, which categorizes storms from 1 to 5 based on maximum sustained one-minute winds, ranging from 119-153 km/h for Category 1 to over 252 km/h for Category 5. Notable examples illustrate the destructive potential and variability of tropical cyclones. Hurricane Katrina in 2005 underwent two periods of rapid intensification in the Gulf of Mexico, reaching Category 5 status with sustained winds of 175 mph before weakening to Category 3 at U.S. landfall, causing over 1,800 deaths and $125 billion in damages primarily from storm surge and flooding. Similarly, Tropical Cyclone Idai in 2019 made landfall in Mozambique as a Category 3 equivalent, with winds exceeding 220 km/h, leading to over 600 deaths across southern Africa, widespread flooding, and agricultural losses of nearly 780,000 hectares in Malawi, Mozambique, and Zimbabwe. In the 2020s, Hurricane Helene in September 2024 rapidly intensified to Category 4 status before landfall in Florida, causing catastrophic inland flooding across the southeastern U.S., over 230 deaths, and damages exceeding $50 billion. Observed trends indicate a poleward migration of tropical cyclone tracks and an increase in rainfall intensity, with the attributing high confidence to anthropogenic warming causing a global rise in extreme tropical cyclone precipitation rates, projected to intensify by 10-20% per degree Celsius of warming due to enhanced atmospheric moisture capacity. Tropical cyclones dissipate rapidly when they move over land or cooler ocean waters, as the supply of warm, moist air is cut off, reducing latent heat release and increasing surface friction that disrupts the low-level inflow. Over land, drier air and higher roughness further weaken the system, often reducing winds below hurricane force within 12 hours, while over cold water below 26.5°C, upwelling of cooler layers starves the storm of energy. This transition typically results in the cyclone filling its low-pressure center and losing its organized structure.

Subtropical Cyclones

Subtropical cyclones are hybrid low-pressure systems that exhibit a blend of tropical and extratropical characteristics, typically forming in transitional latitudes between 20° and 40° where baroclinic and convective processes interact. These storms feature an asymmetric structure, with distinct warm and cold sectors, a large cloud-free or lightly clouded center, and heavy thunderstorm activity often displaced more than 100 miles (160 km) from the circulation core. Unlike fully symmetric tropical cyclones, subtropical systems derive significant energy from both latent heat release and baroclinic instability, resulting in a partial warm core at low levels but often a cold core aloft. They generally tolerate moderate vertical wind shear better than tropical cyclones but remain sensitive to environmental conditions that favor extratropical development. Formation of subtropical cyclones often occurs through interactions between extratropical systems and tropical moisture, such as the merger of a mid-latitude trough with a monsoon trough or the evolution of an extratropical cyclone over subtropical waters warmer than 21°C (70°F). This process warms the storm's core via latent heat from organized convection, shifting energy sources toward those resembling tropical systems while retaining frontal or baroclinic features. Some subtropical cyclones can further intensify over warm ocean surfaces, transitioning into full tropical hurricanes if convection reorganizes near the center and symmetry increases; for instance, the 1968 Subtropical Storm One in the Atlantic briefly achieved tropical status before recurvature. Dynamically, these cyclones are distinguished by their thermal structure, with a low-level warm core supporting convective activity and an upper-level cold core enhancing divergence, allowing for moderate intensification despite asymmetry. Classification often relies on the Cyclone Phase Space (CPS) technique, which uses metrics like the thermal index (B parameter)—the difference in 900–600 hPa geopotential thickness across the storm track—and thermal wind components to identify hybrid phases. In the CPS, subtropical cyclones occupy a transitional quadrant where low-level thermal winds indicate a warm core (|−VT-L| > 0) and upper-level winds a cold core (−VT-U| < 0), with |B| values between 0 and 10 m signaling partial . Notable examples include Subtropical Storm Andrea in 2007, which formed off the southeastern U.S. coast from an extratropical precursor and brought heavy rains to before transitioning extratropically. In the Mediterranean, subtropical cyclones like the 2011 "medicane" off developed from baroclinic lows interacting with warm sea surface temperatures, producing intense convection and gale-force winds. Rare subtropical bomb cyclones, characterized by rapid deepening at subtropical latitudes, have occurred in the Atlantic, such as the 1998 system that explosively intensified near due to warm seclusion dynamics. More recently, Subtropical Storm Biguá formed in December 2024 off southern Brazil, the first such named storm in the South Atlantic basin, bringing heavy rainfall and flooding to . Recent analyses suggest that may contribute to an increasing frequency of such hybrid systems through enhanced subtropical moisture availability and altered baroclinicity, though attribution remains uncertain.

Polar Lows

Polar lows are intense, small-scale (mesoscale to synoptic) cyclones that develop over polar regions during winter, primarily in association with marine cold air outbreaks from or snow-covered landmasses. These systems typically exhibit diameters ranging from 200 to 1000 km and persist for 1 to 3 days, generating gale-force surface winds exceeding 15 m/s and resembling weakened tropical hurricanes in structure, though they form over relatively colder seas adjacent to ice edges. Unlike larger synoptic-scale cyclones, polar lows are driven by localized convective processes rather than broad baroclinic , leading to and heavy , which can pose hazards to maritime activities in high-latitude regions. The formation of polar lows relies on convective arising from a significant air-sea contrast, typically exceeding 7°C, where cold polar air advected over warmer open releases through deep . This process often initiates near the ice edge, with symmetric polar lows developing via cooperative interaction between and rotation (conditional of the second kind, or CISK), while asymmetric types form under stronger baroclinic influences from upstream fronts. The weaker effective Coriolis force on their small scales, combined with the absence of pre-existing large-scale typical in tropical environments, distinguishes their dynamics from those of tropical cyclones, resulting in shorter lifespans and less organized eye structures. Recent studies emphasize that these systems require sufficient extent to generate the necessary cold outbreaks, with reduced contrasts limiting development. In the , polar lows frequently occur in the Norwegian and s, where climatological analyses indicate approximately 20 events per winter season in the alone, based on satellite and reanalysis data from extended winter periods. Notable examples include the intense polar low observed over the in January 2019, which produced winds up to 25 m/s and disrupted shipping routes. analogs, though less frequent and often more baroclinic in nature, have been documented over the Weddell and Bellingshausen Seas, sharing similar convective triggers but influenced by the Southern Ocean's stronger zonal flow. Post-2020 research links a projected decline in polar low frequency to sea ice loss, which diminishes cold air outbreak intensity and air-sea temperature gradients under future warming scenarios.

Upper-Level Cyclones

Polar Cyclones

Polar cyclones, also known as upper-level polar vortices or cut-off lows in the , are synoptic-scale disturbances primarily occurring in the mid-to-upper , often centered around the 500 hPa level. These systems are characterized by closed cyclonic circulations detached from the main westerly flow, featuring a cold core with temperatures as low as -30°C at 500 hPa, forming cold pools aloft that enhance (PV) anomalies and promote closed contours. Typical diameters range from 500 to 2000 km, allowing them to influence large regions equatorward of the . The formation of polar cyclones arises from geostrophic adjustment processes triggered by breaking along the polar jet, where amplified planetary waves lead to the pinching off of troughs and the creation of isolated positive PV anomalies in the upper . This breaking isolates a portion of the polar from the broader circulation, resulting in a self-sustaining vortex through the balance of Coriolis forces and pressure gradients. These anomalies propagate slowly and can persist for several days, distinct from the faster-moving troughs in the synoptic-scale flow. In terms of impacts, polar cyclones induce surface pressure falls through upper-level divergence, which can destabilize the lower and facilitate the development of secondary surface systems, including the triggering of polar lows during cold air outbreaks over polar seas. A notable example is the role of upper-level polar cyclones in the European cold outbreaks, where disrupted patterns led to prolonged cold anomalies and stormy conditions across the continent, exacerbating weather extremes. Their dynamics are governed by barotropic instability, arising from horizontal shear in the that amplifies small perturbations into coherent vortices, with energy transfer occurring primarily within the same tropospheric level. Recent research from 2023 emphasizes the stratospheric influence on polar cyclones via sudden stratospheric warmings (SSWs), which weaken the and propagate downward, enhancing activity and increasing the frequency of wave breaking events that spawn these upper-level systems. These interactions highlight a coupled stratosphere- pathway, where SSW-induced circulation changes can precondition the jet for instability, leading to more persistent polar cyclones in the . As of 2025, studies indicate that polar cyclones are forming more frequently and intensifying, potentially acting as a missing link in sea ice depletion models under . Such findings underscore the need for integrated modeling of stratospheric-tropospheric coupling to improve forecasts of polar weather extremes.

Tropical Upper Tropospheric Trough (TUTT) Cells

Tropical upper tropospheric trough (TUTT) cells are discrete, closed cyclonic circulations embedded within the broader semipermanent TUTT, a feature of the summer upper-tropospheric circulation in the tropics. These cells typically occur between 100 and 400 hPa, with maximum relative centered between 150 and 200 hPa, and exhibit pronounced negative anomalies peaking at 200 hPa alongside cold temperature anomalies in the 650–200 hPa layer. Approximately 75% of identified TUTT cells have radii less than 500 km, with central heights at 200 hPa below 1239.4 , and they form part of the quasi-stationary planetary wave pattern that persists over tropical basins during the warm season. Cyclonic is prominent in the 550–125 hPa layer, distinguishing these features as upper-level cold-core lows that contribute to the overall trough structure. TUTT cells primarily form through the southward intrusion of midlatitude troughs into the climatological position of the TUTT, often initiating east of 150°E in the western North Pacific where they develop from initial height perturbations. Divergence arising from organized monsoon convection supports their intensification by promoting upward motion and easterly momentum transport in the upper , which helps maintain the trough's elongated structure. In some cases, tropical cyclones contribute to cell formation via the downstream dispersion of short energy, leading to two distinct types depending on the ambient vertical : broader troughs in weak anticyclonic shear or more isolated cells in stronger shear environments. These cells play a key role in tropical cyclone genesis by seeding upper-level vorticity and providing divergent outflow that enhances low-level convergence and in underlying disturbances, particularly when positioned to minimize vertical . For instance, the North Pacific TUTT, extending east-northeastward from about 35°N into the eastern Pacific, influences cyclone development in that basin by steering flows and altering shear profiles. Similarly, in the Atlantic, the TUTT supports early-season activity through reduced shear and enhanced ascent over potential genesis regions. In their evolution, TUTT cells typically propagate westward at an average speed of 6.6 m s⁻¹ with a mean lifespan of about 4.4 days, maturing in the central basin before weakening and contracting farther west. They can spawn mid-level cyclonic vortices through the descent of anomalies to lower levels, inducing surface disturbances via upper-level divergence on their eastern flanks. Observations reveal interannual variability linked to the El Niño-Southern Oscillation (ENSO), with reduced frequency and eastward shifts during El Niño phases due to anomalous warming in the central-eastern tropical Pacific that weakens the trough's amplitude.

Mesoscale Vortices

Mesocyclones

A is a deep, persistently rotating updraft within a severe , typically associated with storms and serving as a precursor to formation. These vortices form on the mesoscale, distinguishing them from larger synoptic cyclones by their convective origins and short lifespans of 30-60 minutes. Mesocyclones are most common in environments with strong vertical , enabling the organization of thunderstorm updrafts into rotating structures. Mesocyclones exhibit characteristic dimensions of 2-10 km in horizontal diameter and 3-5 km in vertical extent, with rotational tangential speeds ranging from 20-50 m/s. This scale allows them to encompass much of the storm's mid-level , producing significant through dynamic processes. The rotation is cyclonic in the , often intensifying in the storm's rear flank. Formation of mesocyclones occurs primarily through the tilting and of horizontal generated by environmental in thunderstorms. Horizontal , arising from veering winds with height, is tilted into the vertical by the and amplified by as air parcels accelerate upward, leading to when storm-relative helicity exceeds 150 m²/s² in the 0-3 km layer. This threshold indicates sufficient streamwise for sustained mesocyclone development, particularly in right-moving . Detection of mesocyclones relies on , which identifies them through couplets in storm-relative velocity data and associated echoes in reflectivity patterns. The echo forms as wraps around the rotating in the storm's rear flank, a signature often preceding tornadoes. In the U.S. Plains, notable examples include the May 3, 1999, outbreak in and , where multiple supercells produced mesocyclones detected by WSR-88D radars, contributing to 63 tornadoes including an F5. Similar radar signatures were observed during the April 10, 1979, Red River Valley outbreak, highlighting mesocyclones' role in prolific tornadic events across and . Recent advances in have enhanced nowcasting by improving -based detection and prediction in severe . In , the TorNet dataset, comprising over 200,000 images, enabled models to predict formation from signatures with up to 85% accuracy for stronger events, reducing false alarms in operational forecasting. Additionally, approaches incorporating polarimetric variables have improved short-term nowcasting of hazards, including evolution, by fusing multi-source data for lead times of 0-30 minutes. These methods leverage convolutional LSTM architectures to track rotational features, outperforming traditional algorithms in real-time applications.

Tornadoes

Tornadoes are violently rotating columns of air that extend from a to the ground, typically forming as narrow surface vortices spawned by the within thunderstorms. These destructive phenomena can produce wind speeds exceeding 100 m/s (over 224 mph) in their most intense manifestations, posing severe threats to life and property through structural devastation, airborne debris, and rapid onset. Unlike broader mesocyclones, tornadoes manifest as concentrated funnels of , distinguishing them by their surface-level intensity and narrower scale. Tornadoes typically exhibit diameters ranging from 50 to 500 meters, though averages hover around 50 meters, with path lengths varying from 1 to 100 kilometers depending on duration and terrain. Wind speeds are estimated using the Enhanced Fujita (EF) scale, implemented by the in 2007, which categorizes intensity from EF0 (65-85 mph) to EF5 (over 200 mph) based on damage to 28 specific indicators like buildings and trees. This scale provides a damage-based proxy for winds, as direct measurements are rare due to the hazards involved. Formation often occurs via the dynamic pipe effect, where intense descent within the stretches and narrows the rotating air column into a , frequently facilitated by the rear-flank downdraft (RFD)—a downdraft of cooler air wrapping around the storm's rear that enhances low-level convergence and . The RFD creates a gust front that undercuts the , promoting the "pipe-like" intensification of from mid-levels downward. Tornadoes are classified into and non- types; variants, comprising the majority of strong events, include wide tornadoes (appearing broader than tall) and multivortex structures featuring multiple sub-vortices rotating within the main funnel, amplifying damage potential. Non- tornadoes, such as gustnados, arise from outflow boundaries without organized rotation and are generally weaker and shorter-lived. Globally, approximately 75% of documented tornadoes occur , attributed to favorable geography combining moist Gulf air, dry western winds, and upper-level jet streams. Notable examples include the May 22, 2011, , EF5 tornado, which carved a 22-mile path with winds up to 200 mph, killing 161 people and injuring over 1,000 in one of the deadliest U.S. events since 1947. More recently, the March 24, 2023, Rolling Fork–Silver City EF4 tornado in , part of a multi-day outbreak, traveled 59 miles with peak winds near 190 mph, resulting in 17 fatalities and near-total destruction of the town. U.S. tornado reports have shown a slight increase over recent decades, largely due to enhanced radar technology, , and improved reporting rather than unequivocal climate-driven intensification.

Waterspouts

Waterspouts are intense, rotating columns of air that form over bodies of water, resembling tornadoes but distinguished by their maritime environment and often featuring a visible spray vortex at the base composed of sea spray and mist pulled upward by the vortex. These vortices connect a cumuliform cloud base to the water surface, creating a funnel-like appearance, and can pose hazards to maritime activities due to sudden high winds and turbulence. Unlike land-based tornadoes, waterspouts typically exhibit a cooler air mass near the surface because the underlying water moderates temperatures, and the water's frictional drag often limits their intensity compared to terrestrial counterparts. Waterspouts are classified into two primary types: tornadic and fair-weather. Tornadic waterspouts develop in association with mesocyclones within severe s, exhibiting wind speeds often exceeding 50 m/s (approximately 113 mph), which can rival those of land tornadoes and cause significant structural damage if they make . In contrast, fair-weather waterspouts arise from surface-level convergence without thunderstorm involvement, typically producing winds below 40 m/s (about 89 mph) and remaining weaker due to the absence of intense updrafts. Tornadic types are rarer but more destructive, while fair-weather varieties are more common and visually striking but generally less hazardous. Formation of waterspouts mirrors aspects of tornado genesis but is adapted to aquatic conditions. Tornadic waterspouts originate analogously to land tornadoes, with rotation intensifying downward from a thunderstorm's mesocyclone toward the water surface, often fueled by warm, moist air over coastal regions. Fair-weather waterspouts, however, emerge from cumulus cloud convection interacting with convergent sea breezes or boundary layer instabilities, where warm water heats the overlying air, promoting upward motion and vortex development from the surface. These phenomena are prevalent in areas with frequent cumulus activity and warm seas, such as the Florida Keys—where 20 to 70 events occur annually from May to September—and the central-eastern Mediterranean, where summer and autumn outbreaks are documented due to similar convective setups. The lifecycle of a waterspout is characteristically brief, lasting 5 to 20 minutes for most fair-weather events, though tornadic ones may persist longer if supported by ongoing thunderstorm dynamics. Fair-weather waterspouts progress through five overlapping stages: an initial dark spot on the water indicating convergence; a spiral pattern of surface currents; formation of a spray ring as the vortex strengthens; maturation into a fully developed funnel with maximum intensity; and rapid decay, often triggered by downdrafts or interaction with land, where they quickly lose energy. Upon , waterspouts generally weaken and dissipate due to increased surface and the loss of the warm, moist water source, though tornadic variants can transition into damaging tornadoes. For instance, a notable outbreak of over 25 fair-weather waterspouts occurred off the Mediterranean coast on , 2006, highlighting their potential for multiple simultaneous formations in conducive environments.

Boundary Layer Vortices

Dust Devils

Dust devils are small-scale, short-lived vortices that form in the atmospheric boundary layer over arid or semi-arid surfaces, driven primarily by thermal convection rather than organized deep moist convection. These phenomena are characterized by rotating columns of air that entrain loose dust and debris from the ground, rendering them visible as narrow, towering funnels of particulate matter. Unlike larger convective storms, dust devils typically dissipate within minutes and pose minimal structural threat, though they can occasionally cause minor hazards such as reduced visibility or light debris damage. Typical dust devils exhibit diameters ranging from 10 to 100 meters, with heights extending from 100 to 1,000 meters above the surface. Wind speeds within these vortices generally reach 10 to 30 meters per second, though larger examples can exceed 25 meters per second. The visibility of dust devils stems from the of fine particles, which are suspended in the core and along the vortex walls, often creating a dusty, translucent column that contrasts against the clear sky. Formation occurs through diurnal surface heating, where intense solar radiation warms the ground, generating buoyant or plumes of that rise rapidly into cooler overlying air. Ambient then imparts rotation to these updrafts, tilting and organizing them into coherent vortices; this process is most efficient in calm to light wind conditions over dry, flat terrain. Dust devils are prevalent in desert environments, such as the in and the , where loose, fine-grained soils and extreme daytime temperatures facilitate their development, often peaking in late morning to early afternoon. In terms of intensity, dust devils are generally classified using an analog to the Fujita (F) scale for tornadoes, most commonly falling into F0 or F1 categories, corresponding to wind speeds of 18 to 50 meters per second and capable of causing light damage like uprooting small plants or scattering lightweight objects. Stronger dust devils, though rare, can approach F1 limits but lack the sustained power of true tornadoes due to their thermal rather than dynamic origins. Climatologically, dust devils number in the dozens to hundreds per day during peak seasons in hot, arid regions; for instance, mean occurrences of 50 to 80 have been observed near . They occur most frequently from to in areas like the central , contributing modestly to regional dust transport by injecting fine aerosols into the lower atmosphere, though their overall impact on global dust budgets remains secondary to larger storm systems. In the southwestern U.S., such as , they are a common feature of the season.

Steam Devils

Steam devils are rare, small-scale atmospheric vortices that form over warm bodies of water during cold air outbreaks, characterized by their visibility due to entrained condensing or . These phenomena typically exhibit diameters ranging from 5 to 50 meters, heights up to several hundred meters, and lifespans of just a few minutes, with rotational wind speeds generally below 20 m/s. They appear as narrow, rotating columns rising from the water surface, often tilted by ambient winds, and are distinguished by their gentle, non-destructive nature, posing minimal impact to surroundings. Unlike larger convective systems, steam devils lack deep vertical development and association with thunderstorms, remaining confined to the near-surface . The formation of steam devils is analogous to that of dust devils but occurs over surfaces, driven by intense surface heating from relatively warm lakes or seas under overlying cold, dry air, typically in fall or winter conditions. This temperature contrast generates shallow convective plumes within superadiabatic boundary layers, where instability and induce rotation, drawing up steam fog—also known as Arctic sea smoke—into visible whirls. For instance, air temperatures as low as -21°C over near 0°C can produce the necessary , with winds enhancing without overwhelming the structures. These vortices are most common in regions like the during early winter Arctic outbreaks, where unfrozen persists amid freezing air. Notable examples include multiple steam devils observed over on January 31, 1971, during an Arctic outbreak, where columns up to 450 meters tall rotated slowly amid 18 m/s gusts, captured from the shoreline. Similarly, on January 15, 2009, abundant steam devils formed over in , rising tens of meters from in unstable air, documented via video showing their shallow, short-lived nature. In Arctic seas, steam devils accompany widespread during polar outbreaks, though specific cases are less documented due to remote locations. Overall, steam devils receive far less research attention than dust devils, with studies primarily limited to observational reports from cold-season lake events. A key distinction from dust devils lies in their reliance on moisture condensation for visibility and structure, rather than lofted particulate matter, resulting in cleaner, vapor-filled cores with negligible environmental disruption. Steam devils represent a subtype of vortices, emphasizing the role of surface contrasts in generating small-scale rotations.

Fire Whirls

Fire whirls are intense, rotating columns of flame and hot gases that form within large-scale fire environments, such as wildfires or firestorms, driven primarily by from heated air and that imparts rotation. These vortices differ from typical atmospheric cyclones by their direct dependence on the fire's , creating a self-sustaining chimney-like that draws in surrounding air and amplifies the swirl. They typically manifest in two forms: smaller, dust devil-like whirls that are transient and localized, or larger, tornado-like structures that can persist and cause widespread disruption. Characteristics of fire whirls include diameters ranging from 1 to 10 , heights generally up to 40 but occasionally exceeding 1 kilometer in extreme cases, and wind speeds of 20 to 70 per second (45-160 mph) within the core. The smaller variants resemble dust devils in scale and brevity, lasting seconds to minutes, while tornado-like fire whirls can endure for over 20 minutes with rotational velocities approaching those of an EF3 . These dimensions and intensities arise from the balance between buoyant forces and viscous dissipation, often modeled using a framework for scaling, where the tangential velocity profile features solid-body rotation in the inner (proportional to ) and an inverse- decay in the outer free-vortex region, allowing prediction of whirl height and strength based on heat release and ambient . Formation begins with the thermal chimney effect, where intense heating from a creates rising columns of buoyant air, establishing a low-pressure core that entrains cooler ambient air and generates upward velocities. This process is often enhanced by terrain channeling, such as in valleys or canyons, where converging winds introduce and focus the flow, tilting horizontal vortices into vertical alignments that intensify into full whirls. In and field studies, the transition to a sustained requires a critical swirl number, typically around 0.5 to 1.0, beyond which the vortex stabilizes and grows. Notable examples include the fire tornado during the 2018 in , which reached an estimated EF3-equivalent intensity with winds of 143 mph (64 m/s) and caused extensive structural damage by lofting burning debris across the landscape. Similarly, the 1945 firestorm, triggered by the atomic bombing, generated massive updrafts that formed whirlwinds amid the conflagration, contributing to winds exceeding 50 m/s and accelerating the spread of flames over a wide . These events highlight how fire whirls can scale from localized phenomena to catastrophic vortices under extreme fuel loads and meteorological conditions. Fire whirls pose significant hazards by accelerating fire spread through the transport of embers and burning debris, which can ignite spot fires kilometers away from the main front, complicating suppression efforts and endangering firefighters. The intense and lifting forces within the vortex can also uproot trees, hurl vehicles, and generate pressures sufficient to damage buildings, as observed in multiple incidents. Analyses of the 2024-2025 season across the indicate that made burned areas up to 30 times larger in regions like and as of October 2025.

Extraterrestrial Cyclones

Cyclones on Gas Giant Planets

Gas giant planets, such as and Saturn, host enormous, long-lived cyclones in their thick hydrogen-helium atmospheres, driven by internal heat sources and rapid planetary rotation rather than surface interactions seen on . These vortices can span thousands of kilometers and persist for decades or longer, contrasting with Earth's more transient weather systems due to the absence of a solid surface and the deep, convective nature of atmospheres. Ice giants and , with similar hydrogen-helium envelopes, also exhibit cyclonic activity. In 2023, scientists reported the first observation of a polar cyclone at ' north pole using radio emissions from the , revealing a vortex of warm air beneath the clouds at depths of tens of bars. experiences intense superstorms driven by abundance, confined to the upper atmosphere, with winds reaching hundreds of kilometers per hour, influenced by the planets' extreme axial tilts and seasonal forcing. On Jupiter, NASA's Juno spacecraft discovered stable polygonal arrangements of polar cyclones in 2016-2017, with eight surrounding a central cyclone at the and five at the , each with diameters of approximately 4,000-5,000 kilometers. These cyclones, observed persistently for over eight years through at least 2025, rotate at speeds up to 360 kilometers per hour and exhibit oscillatory motions influenced by interactions with surrounding zonal jets. The iconic , an anticyclone roughly 16,000 kilometers wide historically but shrinking in recent decades, exemplifies related vortex dynamics, feeding on smaller storms amid Jupiter's banded jet streams. Juno's microwave and visible-light observations in the 2020s revealed deep-rooted structures extending hundreds of kilometers below the cloud tops, sustained by shallow-water instabilities akin to ocean eddies on . Saturn's polar regions feature similarly massive cyclones, imaged by NASA's Cassini spacecraft, including a north polar vortex with an eye about 2,000 kilometers across and wind speeds reaching 330 kilometers per hour, encircled by the persistent —a 14,500-kilometer-wide pattern linked to resonances. Cassini data from 2004-2017 showed these vortices extending deep into the atmosphere, with the south polar cyclone comparable in scale. Dynamics on both planets involve deep from internal heat fluxes, interacting with fast zonal jets (up to 500 kilometers per hour on ) and planetary-scale s, which propagate with periods of hours due to rotation periods of about 10 hours—far shorter than Earth's daily cycle. Unlike terrestrial cyclones, these lack frictional dissipation from a surface, allowing multi-decadal stability observed since Voyager flybys in the and confirmed by later missions.

Cyclones on Terrestrial-Like Planets

Terrestrial-like planets and moons, such as Mars, , and Saturn's moon Titan, host cyclones driven by their thin atmospheres and unique surface-atmosphere interactions, contrasting with the deep convective systems of gas giants. These cyclones often span scales from hundreds to thousands of kilometers and are influenced by exotic factors like low gravity, reduced Coriolis effects, and alternative volatile cycles, such as on Titan instead of . Observations from have revealed their seasonal variability and stability, providing insights into planetary dynamics. On Mars, cyclones manifest primarily as dust storms, ranging from local events hundreds of kilometers across to global storms enveloping the planet, which occur seasonally during spring and summer due to perihelion heating and dust lifting. These storms are initiated by baroclinic in the thin CO₂ atmosphere, where low Coriolis forces—resulting from Mars' relatively slow and small size—allow for weaker deflection of air masses compared to , enabling broader, less organized circulations. Topographic features, such as craters and highlands, contribute to spin-up of winds through channelled flows and orographic lifting, amplifying storm intensity. Early observations from the Viking orbiters in the documented global dust storms that obscured the surface for months, while the Curiosity rover's meteorological instruments since 2012 have measured local pressure drops and wind gusts associated with passing cyclones, linking them to larger-scale atmospheric waves. Venus exhibits persistent polar vortices at both poles, with the southern one often displaying a distinctive double-eyed structure—two counter-rotating centers within a larger about 2,000 kilometers wide—sustained by the planet's slow and superrotating atmosphere. These vortices rotate with periods of 2–3 days, far faster than ' 243-day sidereal day, and remain stable due to the weak Coriolis effect from retrograde and minimal seasonal forcing, allowing conservation in the thick but slow-spinning environment. The Japanese Akatsuki orbiter, operational from 2015 until 2024, imaged these features in , revealing thermal contrasts and cloud patterns that indicate in the vortex cores, contrasting with equatorial superrotation. Earlier data from 2006 confirmed the double-eyed morphology through multi-wavelength . On Titan, cyclones appear as polar vortices driven by methane convection in its nitrogen-methane atmosphere, analogous to Earth's but at cryogenic temperatures, with storms forming over hydrocarbon lakes and contributing to seasonal haze redistribution. These vortices, observed at scales of 1,000–3,000 kilometers, weaken during winter due to and stratospheric , as captured by Cassini imaging from 2004–2017, which showed a colorful south with embedded methane clouds. Convection is enhanced by Titan's 15-year seasonal cycle, leading to intense storms that can span mid-latitudes. Overall, cyclones on these bodies typically range from 100 to 5,000 kilometers in diameter, highlighting the role of thin atmospheres in permitting surface-driven dynamics. Similar to small-scale boundary layer vortices like dust devils on Earth and Mars, these planetary cyclones underscore surface-atmosphere coupling in low-pressure environments. Extending to exoplanets, 2024 observations by the detected massive cyclones on the hot Jupiter WASP-121b, where extreme temperature contrasts drive repeated storm formation, offering a glimpse into dynamics on terrestrial-like worlds beyond our solar system.

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