The word "tornado" is a loanword "Loan (linguistics)") from English, which it arrived from the Spanish "tronada", which, according to the RAE, refers to a "thunderstorm".[10]​ The metathesis is undoubtedly due to a reinterpretation of the word under the influence of "tornar".[11]​[12]​.

Contenido

Un tornado se define en el Glossary of Meteorology como «una columna de aire que gira violentamente sobre sí misma, estando en contacto con el suelo, ya sea colgando de o debajo de una nube cumuliforme, y frecuentemente (pero no siempre) visible como una nube embudo...».[13]​ En la práctica, para que un vórtice sea clasificado como un tornado, debe tener contacto tanto con el suelo como con la base de la nube. Sin embargo, los científicos aún no han formulado una definición completa del término; por ejemplo, hay desacuerdos respecto a si múltiples puntos de contacto con el suelo provenientes del mismo embudo constituyen diferentes tornados.[14]​ El término «tornado» se refiere además al vórtice de viento, no a la nube de condensación.[15]​[16]​.

funnel cloud

A tornado is not necessarily visible; However, the low atmospheric pressure inside it and caused by the high wind speed - in accordance with Bernoulli's principle - as well as its rapid rotation (due to cyclostrophic equilibrium) generally cause the water vapor in the air to become visible by condensing in the form of water droplets, taking the form of a funnel cloud or a condensation funnel.[17] When a funnel cloud extends at least half the distance between the ground and the base of the cloud—which is usually less than two kilometers—[18]​ is considered a tornado.[19]​.

There is some disagreement over the definition of “funnel cloud” and “condensation funnel.” According to the Glossary of Meteorology, a funnel cloud is any rotating cloud hanging from a cumulus or cumulonimbus cloud, and therefore most tornadoes fall under this definition.[20] Among many meteorologists, a funnel cloud is defined strictly as a rotating cloud not associated with strong surface winds, and a "condensation funnel" is a term used for any cloud that is rotating beneath a cloud. cumuliform.[14]​.

Tornadoes often start out as funnel clouds without strong surface winds, however, not all of them turn into a tornado. Either way, many tornadoes are preceded by a funnel cloud. Most of them produce strong winds at the surface, while the visible funnel remains far from the ground, making it difficult to distinguish the difference between a funnel cloud and a tornado from a distance.[14]​.

Families and waves

Occasionally, a single storm produces more than one tornado, either simultaneously or in succession. Multiple tornadoes produced by the same storm are known together as a tornado family.[21]​.

Sometimes multiple tornadoes spawn from the same storm system. If its activity is not interrupted, this is considered a tornado surge, although there are several definitions. A period spanning several consecutive days with tornado surges in the same area (generated by multiple weather systems) is a tornado surge sequence, also known as an extended tornado surge.[13]​[22]​[23]​.

Shape and dimensions

Most tornadoes take the shape of a narrow funnel, a few hundred meters wide, with a small expansive cloud of debris near the ground, at least in their initial stage. Tornadoes can be completely obscured by rain or dust, and if so, they are particularly dangerous, since even experienced meteorologists may not see them.

Tornadoes, however, can come in many shapes and sizes. Small and relatively faint landspouts, for example, cannot be seen as anything more than a small whirlwind of dust on the ground. Although the condensation funnel may not extend from the ground, if the associated winds at the surface exceed 40 mph (64 km/h), the circulation is considered a tornado.[15] A tornado with a nearly cylindrical shape and relatively low height is sometimes called a stovepipe tornado.[24] Large tornadoes with a single vortex can be seen as huge buried wedges. on the ground, and are therefore known as "wedge tornadoes."[25] One of these tornadoes can be so wide that it appears to be a group of dark clouds, being even wider than the distance between the cloud base and the ground. Even experienced storm spotters may have difficulty differentiating a wedge tornado and a low cloud in the distance. Many, but not all, of the largest tornadoes are wedge-shaped.[26]​.

Tornadoes in their dissipating stage may look like narrow tubes or ropes, and they often curl or twist into complex shapes. These tornadoes are said to be in their "string phase," or becoming a "string tornado." When they take this shape, the length of their funnel increases, forcing the winds within the funnel to weaken due to conservation of angular momentum.[27] Tornadoes with multiple vortices, for their part, may appear to be a family of eddies rotating around a common center, or they may be completely obscured by condensation, dust, and debris, appearing to be a single funnel.[28]​

In the United States, on average tornadoes are about 150 m wide and travel about 8 km in contact with the ground. Either way, there is a wide range of tornado sizes. Weak tornadoes, or strong dissipating tornadoes, can be extremely narrow, sometimes only a few meters wide. A tornado was once reported to have a destruction zone only 2 m wide. On the other hand, wedge tornadoes can have a destruction zone 1.5 km wide, or even more. A tornado that hit Hallam "Hallam (Nebraska)", Nebraska, on May 22, 2004, was at one point measuring 4 km wide at ground level.[29]​.

In terms of path length, the 1925 Tri-State Tornado, which affected parts of Missouri, Illinois, and Indiana on March 18, 1925, officially touched the ground continuously for 220 miles (352 km). Many tornadoes that appear to have paths of 100 miles or more are actually a family of tornadoes that formed in rapid succession; However, there is no concrete evidence that this occurred in the case of the Tri-State Tornado.[22]​.

Appearance

Tornadoes can come in a wide variety of colors, depending on the environment in which they form. Those that develop in a dry environment can be practically invisible, barely distinguishable only thanks to the debris circulating at the base of the funnel. Condensation funnels that lift little or no debris may be gray or white. When traveling over a body of water, as waterspouts do, they can turn very white or even blue. Funnels that move slowly, consuming large amounts of debris and soil, are generally darker, taking on the color of the debris. Meanwhile, tornadoes in the Great Plains can turn red due to the reddish tint of the earth, and tornadoes in mountainous areas can travel over snow-covered terrain, turning bright white.

An important factor that determines the appearance of a tornado is lighting conditions. A tornado that is being lit from behind (seen with the sun behind it) looks very dark. The same tornado, seen with the sun behind the observer, may appear gray or bright white. Tornadoes that form during sunset can be many different colors, featuring shades of yellow, orange, and pink.[32]​.

Some factors that can reduce the visibility of tornadoes are dust raised by the storm's winds, heavy rain or hail, and darkness of night. Tornadoes that occur under these conditions are particularly dangerous, since only observations from weather radar, or possibly the noise they produce as they approach, serve as a warning to those in their path. In any case, most strong tornadoes form on the base of the storm's updraft, which is free of rain,[33]​ allowing them to be visible.[34]​ Additionally, most tornadoes occur during the afternoon, when the sun can penetrate even the densest clouds.[22]​ Likewise, nighttime tornadoes are generally illuminated due to the frequent appearance of lightning.

There is evidence, including images from mobile Doppler on Wheels radars) and witness reports, that most tornadoes have a clear, calm center where the pressure is extremely low, similar to the "Eye (cyclone)" of tropical cyclones. This area would be clear (possibly dusty), with relatively calm winds, and would be very dark, as the light would be blocked by debris spinning on the outside of the tornado. Those who claim to have seen They say they have achieved the inside of a tornado thanks to the illumination of lightning.[35][36][37]​.

Rotation

Tornadoes are formed by two types of vertical air movements: one anticyclonic with clockwise rotation, formed by cold, dry air that descends, decreasing its radius and therefore increasing its speed of rotation and becoming visible when it reaches the ground (due to the cloud of dust, leaves and other objects) and another ascending one, which constitutes a cyclonic area, whose radius of action increases in a spiral as it ascends counterclockwise in the northern hemisphere, and clockwise in the northern hemisphere. the southern hemisphere. Contrary to what happens with the type of descending anticyclonic funnel, as the hot air rises it widens, losing speed and, obviously, energy. Supercells and tornadoes rotate cyclonically in numerical simulations even when the Coriolis effect is ignored[38]​[39]​ Low-level tornadoes and mesocyclones owe their rotation to complex processes within the supercell and the environment.[40]​ This is the phase of the tornado that is easily visible, since as its height increases and cools, the water vapor it contains condenses in the rising air column, forming a funnel cloud that increases its diameter as it rises although, in return, its rotation speed also decreases.

No obstante lo que se ha indicado, tanto la rotación ascendente hacia la izquierda en el hemisferio norte como la descendente hacia la derecha también en el hemisferio norte, así como la formación de los tornados tipo cuerda y su desplazamiento en su trayectoria superficial se deben al efecto de Coriolis. Ello se debe a la gran dimensión vertical de los tornados, en comparación con su anchura en la superficie: la velocidad de rotación terrestre a los 30° de latitud es de 404 m/s como señala Antonio Gil Olcina.[41]​ Como resulta lógico, esta velocidad genera un efecto intenso en la superficie, donde la fricción hace girar la columna de aire hacia la derecha (de nuevo en el hemisferio norte) mientras que en altura, dicha velocidad es mucho menor al tener la columna o embudo un diámetro mucho mayor.

Todos los tornados comienzan girando en dirección anticiclónica y están formados por una corriente vertical de aire frío y seco que desciende en forma de una espiral que va disminuyendo su radio de giro al ir bajando, con lo que aumenta considerablemente su velocidad de rotación y da origen en compensación, a una espiral ascendente de aire caliente y seco pero que forma rápidamente una nube embudo al enfriarse rápidamente ese aire girando de manera ciclónica, es decir, antihoraria en el hemisferio norte y horaria en el hemisferio sur (mirando desde arriba). La existencia de dos torbellinos simultáneos girando en sentido opuesto en el mismo punto es lo que explica la asimetría de un tornado: siempre tiene una parte abierta, sin nube de condensación a baja altura (por donde desciende el aire frío y seco) y otra por donde asciende el aire caliente y húmedo que, finalmente, puede alcanzar la nube formando una nube embudo por el aumento del diámetro de giro. Generalmente, sólo sistemas tan débiles como las trombas terrestres, los remolinos de arena y los gustnados pueden rotar anticiclónicamente, y usualmente sólo lo hacen aquellos que se forman en el lado anticiclónico de la corriente descendente del flanco trasero") en una supercelda ciclónica.[42]​ No obstante, en raros casos, los tornados anticiclónicos se forman en asociación con el mesoanticiclón") de una supercélula anticiclónica —de la misma forma que un típico tornado ciclónico— o como un tornado acompañante, ya sea como un tornado satélite o asociado con circulaciones anticiclónicas dentro de una supercelda.[43]​.

Sound and seismology

The sounds produced by a tornado are caused by multiple mechanisms. Various sounds produced by tornadoes have been reported over time, often compared to sounds familiar to witnesses and generally as some variation of a roar. Frequently reported sounds include a freight train, rapids or waterfalls, a jet engine, or combinations of these. Many tornadoes are not audible at great distances; The nature and distance of sound propagation depends on atmospheric conditions and topography.

Winds from the tornado vortex and turbulent constituent eddies, as well as the interaction of air currents with the surface and debris, contribute to the creation of sounds. Funnel clouds also make sounds. [44]

Since many tornadoes are audible only when they are very close, noise is not a reliable warning of a tornado. Additionally, any strong wind, even heavy hail or the continuous thunder of lightning in a thunderstorm, can produce a roar similar to that of tornadoes.[45]​.

Tornadoes also produce inaudible infrasonic signatures.[46] Unlike audible signatures, inaudible signatures from tornadoes have been isolated; Due to the long-distance propagation of low-frequency sound waves, attempts are being made to develop devices for the prediction and detection of tornadoes that also serve to understand their morphology, dynamics and formation.[47]​ Tornadoes also produce a detectable seismic signature, and research continues to isolate it and understand its process.[48]​.

Electromagnetism, lightning and other effects

Tornadoes emit in the electromagnetic spectrum, and emissions of atmospheric radio and electric field signals have been detected.[47][49][50] Correlations between tornadoes and patterns of lightning activity have also been observed. Tornadic storms do not contain more lightning than other storms, and some tornadic cells never produce lightning. Generally, cloud-to-ground (cloud-to-ground) lightning activity It decreases when a tornado reaches the surface and returns to its normal level when the tornado dissipates. In many cases, tornadoes and thunderstorms of great intensity exhibit an increase and anomalous dominance of positive polarity in the CG discharges.

The presence of luminosity has been reported in the past, and is likely due to confusion in identifications with external light sources such as lightning, urban lights, and flashes from damaged electrical installations, since internal sources are rarely reported and are not known to have been documented. In addition to winds, tornadoes also present changes in atmospheric variables such as temperature, humidity and pressure. For example, on June 24, 2003, near Manchester, South Dakota, an investigation recorded a pressure deficit of 100 mbar "Bar (unit of pressure)"). The pressure gradually decreased as the vortex approached and then dropped extremely rapidly to 850 mbar at the center of the violent tornado before increasing rapidly as the vortex moved away, resulting in a "V"-shaped pressure graph. At the same time, the temperature tends to decrease and the moisture content to increase in the vicinity of a tornado.[52]​.

Relationship with the supercell

Many tornadoes develop from a type of storm known as supercells.[53] Supercells contain mesocyclones, which are an area of ​​organized rotation of air located in the atmosphere, between 2 and 10 km wide. In addition to tornadoes, heavy rain, lightning, strong gusts of wind, and hail are common in such storms. While most tornadoes, particularly the strongest ones (EF3 to EF5 on the Fujita-Pearson Scale), are derived from supercells, some can also form from other air circulations, and are therefore called non-supercell tornadoes. These types of tornadoes, however, tend to be of lower intensity.[54]​.

Training

Most tornadoes originating in supercells follow a recognizable life cycle. This begins with the origin of the supercell itself, which occurs when a current of cold, dry air descends from the top of a cloud (generally, from the back) to compensate for the warm air that rises from the front to increase the dimensions of the cloud itself. As the cold air is heavier, layers of unstable air are produced where the cold air descends and forces the warm air to rise, creating the storm. If the temperature differences are large enough, the descent of cold air can occur in the form of a vortex, invisible because it is dry air: it becomes visible when, upon reaching the ground, it begins to raise dust, leaves and other objects. This descending air, called the rear flank downdraft (RFD), accelerates as it approaches the ground, and drags the supercell mesocyclone towards it.[15]​ The updrafts, for their part, attract the air around them, increasing the rotation and becoming a narrow column, known as a funnel cloud, which increases in diameter and decreases in spin speed as it rises.[54]​.

When a column of cold, dry air descends with an anticyclonic gyre, that is, with a clockwise rotation (coming from the top of a vertically developing cloud) towards the ground due to the greater density of the cold air, a condensation funnel begins to form (visible by the condensation of humid air as it ascends) in the opposite direction (that is, cyclonic), which compensates for the loss of cloud mass that previously descended, forming the rotating wall cloud. As the anticyclonic funnel descends (RFD) and reach the ground, it creates a gust front") that can cause damage a good distance from the tornado. Usually, the funnel cloud develops into a tornado very soon after the RFD hits the ground.[15]​.

Maturity

Initially, the tornado has a good source of warm, moist air entering it to give it energy, so it grows until it reaches its mature stage. This can last a few minutes or more than an hour, and it is during this time that the tornado generally causes the most damage and its dimensions reach their maximum, measuring in some cases more than 1.5 km wide. Meanwhile, the RFD, which at this stage is an area of ​​cold surface winds, begins to settle around the tornado, disrupting the flow of warm air that feeds it.[15]​.

Dissipation

When the RFD completely envelops the tornado and cuts off its air supply, the vortex begins to weaken, becoming thin, rope-like. This is the dissipation phase, which normally lasts no more than a few minutes, after which the tornado fades away. During this stage the shape of the tornado depends largely on the winds of the main storm, which can cause it to take unusual shapes.[22]​[31][32]​ Even though the tornado is disappearing, it is still capable of causing damage. By becoming a thin tube, in the same way that a skater draws in his arms to spin faster, the winds can increase their speed at this point.[15]​.

With the tornado entering its dissipation stage, its associated mesocyclone usually also weakens, also because the RFD cuts off the airflow that feeds it. As the first mesocyclone and its associated tornado dissipate, the storm flow may concentrate in a new area closer to its center. If a new mesocyclone forms, the cycle can repeat, producing one or more new tornadoes. Occasionally, the old and new mesocyclones produce tornadoes at the same time.

Although this theory of how tornadoes arise, develop, and disappear is widely accepted, it does not explain the formation of smaller tornadoes, such as landspouts or tornadoes with multiple vortices. All of them have different mechanisms that influence their development, however, most follow a pattern similar to the one described here.[55]​.

real tornadoes

A multiple vortex tornado or multivortex tornado is a type of tornado in which two or more columns of moving air rotate around a common center. Multivortex structures can occur in almost any air circulation, but are frequently observed in intense tornadoes. These vortices generally create small areas that cause greater damage along the path of the main tornado.[14] This phenomenon is different from the satellite tornado, which is a weaker tornado that forms very close to another larger, stronger tornado, contained within the same mesocyclone. The satellite tornado appears to "orbit" around the larger tornado (hence the name), resembling a multivortex tornado. However, the satellite tornado is a different circulation, and is much smaller than the main funnel.[14]​.

The waterspout or waterspout is simply a tornado that is over the water. However, researchers generally distinguish tornadic from non-tornadic waterspouts. Non-tornadic waterspouts are less strong but much more common, and are similar in their dynamics to so-called dust devils and landspouts. They form at the bases of cumulus congestus clouds in tropical and subtropical waters. They have relatively weak winds, smooth walls with laminar flow, and generally travel very slowly, if at all. They commonly occur in the Florida Keys, the Río de la Plata, the Paraná River, and the northern Adriatic Sea.[56][57][58] In contrast, tornadic waterspouts are literally "tornadoes over water." They form over it in a similar way to mesocyclonic tornadoes, or they are land tornadoes that reach the water. Since they form from strong storms and can be much more intense, faster and longer lasting than non-tornadic waterspouts, they are considered more dangerous.[59]​.

A landspout, also called a non-supercellular tornado, tornado or funnel cloud, or landspout, is a tornado that is not associated with a mesocyclone. Its name comes from its name as a "non-tornadic waterspout over land." Waterspouts and landspouts share several distinctive characteristics, including their relative weakness, short duration, and a small, smooth condensation funnel that often does not touch the ground. These tornadoes also create a distinctive laminar cloud of dust when they make contact with the ground, because their mechanics are different from those of mesoform tornadoes. Although they are generally weaker than classic tornadoes, they can produce strong winds that are still capable of causing serious damage.[14]​[15]​.

Tornado-like circulations

A gustnado is a small vertical eddy associated with a gust front or downburst. Since they are not technically connected to the base of a cloud, there is some debate about whether gustnadoes are tornadoes. They form when a flow of cold, dry, fast air from a thunderstorm encounters a mass of warm, moist, stationary air near the boundary of the flow, resulting in a “rounding” effect (exemplified by a rolling cloud). If the wind shear at lower levels is strong enough, the rotation can become horizontal or diagonal and make contact with the ground. The result is a taste.[14]​[60]​.

A dust devil or sand and dust devil, known in English as a dust devil (literally translated as "dust devil"), resembles a tornado in that it is a rotating vertical column of air. However, they form under clear skies and rarely reach the strength of weaker tornadoes. They develop when a strong downward current of air "Subsidence (meteorology)") reaches the ground, causing a clockwise whirlpool (again, in the northern hemisphere) that raises dust, leaves and other objects, potentially causing minor or medium damage to homes and other infrastructure works. The fact that they form on clear days is sufficient proof of the anticyclonic nature of this phenomenon. The clear atmosphere indicates meteorological stability (no clouds, as can be seen in both images). What happens is that the contact of the descending cold air with the ground that is very hot due to solar radiation automatically generates a heating of that cold air, with the consequent convection process and which usually also cools down very quickly upon reaching a certain height. It corresponds to those days at the beginning of spring when the air temperature is quite cold but the solar radiation is very intense. In both the image on the left and in the video on the right you can see the characteristics of a dust devil: clear skies and rotation or clockwise rotation (anticyclonic), that is, from left to right because it is in the northern hemisphere. This type of spin is evident in the case of the video and despite this evidence, the origin and dynamics of tornadoes have not yet been well understood, which, as is the case with all types of cyclones, consist of two columns of air, one descending or subsiding and the other ascending or convective. And all cyclonic phenomena have the same structure and the same development. The variations between one phenomenon and another (tornado, gustnado, dust devil, landspout, etc.) are matters of meteorological differences and their scale.

Those circulations that develop near forest fires are called fire whirlwinds or whirlwinds. They are not considered tornadoes except in the rare case that they connect to a pyrocumulus cloud or another cumuliform cloud above them. Fire whirls are generally not as strong as storm-related tornadoes. However, they can cause considerable damage.[22]​.

A steam devil is a term used to describe a rotating updraft involving steam or smoke. A steam whirl is very rare, but is formed primarily from smoke emitted from the chimneys of a power plant. Hot springs and deserts can also be suitable areas for the formation of a steam vortex. This phenomenon can occur over water, when cold arctic air meets relatively warm water.

The Fujita-Pearson Scale and the so-called Enhanced Fujita Scale classify tornadoes according to the damage caused. The enhanced scale (EF) was a refinement of the old Fujita scale, using wind estimates and better description of damage; However, it was designed so that a tornado rated on the Fujita scale would receive the same numerical rank, and was implemented beginning in the United States in 2007. An EF0 tornado, the weakest on the scale, is likely to damage trees but not structures, while an EF5 tornado, the strongest, can rip buildings from their foundations, leaving them exposed and even deforming skyscrapers. The similar TORRO scale ranges from T0 for extremely weak tornadoes to T11 for the most powerful tornadoes known. Data obtained from pulse Doppler radar, photogrammetry, and patterns on the ground (cycloidal signatures) can also be analyzed to determine intensity and give a range.[14]​[61][62]​.

Tornadoes vary in intensity regardless of their shape, size and location, although strong tornadoes are generally larger than weak ones. The relationship with the length of its path and duration also varies, although tornadoes with a longer path tend to be stronger.[63]​ In the case of violent tornadoes, they only present great intensity in a portion of the path, much of this intensity coming from subvortices.[22]​.

In the United States, 80% of tornadoes are classified as EF0 and EF1 (T0 to T3). The higher the intensity of a range, the lower its incidence rate, since less than 1% are violent tornadoes (EF4, T8 or stronger).[64]​ Outside of Tornado Alley, and North America in general, violent tornadoes are extremely rare. Apparently this is due more than anything to the lower number of tornadoes in general outside that region, since research shows that the distribution of tornadoes according to their intensity is quite similar worldwide. A few major tornadoes occur each year in Europe, areas of south-central Asia, portions of southeastern South America, and southern Africa.[65]​.

En los Estados Unidos se presentan más tornados que en cualquier otro país: unas cuatro veces más que los que se estima que se forman en toda Europa, sin incluir trombas marinas.[66]​ Esto se debe principalmente a la geografía única del continente americano. América del Norte es relativamente grande y se extiende desde la zona intertropical hasta las áreas árticas, y no cuenta con una cadena montañosa importante que vaya de este a oeste y que bloquee el flujo de aire entre estas dos zonas. En las latitudes centrales, donde ocurren la mayor parte de los tornados, las Montañas Rocosas bloquean la humedad y el flujo atmosférico, permitiendo que exista aire más seco en los niveles intermedios de la tropósfera, y causando la formación de un área con presión baja al este de dichas montañas. Un incremento en el flujo de aire desde las Rocosas propicia la formación de una línea seca") cuando el flujo es fuerte en los niveles superiores,[67]​ mientras el golfo de México, al este, proporciona abundante humedad en los niveles bajos de la atmósfera. Esta topografía única provoca muchas colisiones de aire cálido con aire frío, que son las condiciones que crean tormentas fuertes y duraderas. Una gran parte de estos tornados se forman en dicha área del centro de los Estados Unidos entre las Rocosas y el golfo, conocida como Tornado Alley («callejón de los tornados»).[3]​ Esta área abarca también partes de Canadá, principalmente en Ontario y las praderas canadienses, aunque el sudeste de Quebec, el interior de Columbia Británica y el occidente de Nuevo Brunswick también son propensos a tornados.[68]​ En ocasiones también se presentan tornados fuertes en el noreste de México. En promedio, en los Estados Unidos ocurren unos 1200 tornados por año.

Fuera de EE. UU., los Países Bajos presentan el mayor número de tornados por área de cualquier país al registrarse allí más de 20 tornados, lo que equivale a 0.00048 tornados/km² anualmente, seguidos por el Reino Unido que presenta anualmente unos 33, es decir, 0.00013 tornados/km², mientras que en Argentina, se registran unos 30 por año, a lo que va 0.0009 tornados/km², mayormente en la zona de llanuras comprendida por el área central y norte de la provincia de Buenos Aires, Córdoba "Provincia de Córdoba (Argentina)"), Santa Fe, Entre Ríos, Santiago del Estero, Chaco y Formosa, habiéndose registrado por ejemplo trombas marinas en la localidad de Mar del Tuyú.[69]​ En números absolutos, sin importar la extensión territorial;[70]​[71]​ de cualquier forma, la mayoría son pequeños y causan muy poco daño, el Reino Unido experimenta más tornados que cualquier país europeo, a la vez que Argentina representa la mayor cantidad de tornados que cualquier país latinoamericano, el segundo en América (detrás de Estados Unidos), y también del mundo incluyendo trombas marinas, en Argentina como también en el Reino Unido.[66]​.

Los tornados matan un promedio de 179 personas por año en Bangladés, por mucho la mayor cantidad dentro de un país en el mundo. Esto se debe a su elevada densidad de población, deficiente calidad de las construcciones, carencia de conocimientos acerca de medidas de seguridad para combatir a los tornados y otros factores.[72]​[73]​ Otros países del mundo que cuentan con tornados frecuentemente incluyen a Argentina, Sudáfrica, en Brasil en la frontera con Argentina, Australia y Nueva Zelanda, así como porciones de Europa y Asia.[6]​[74]​.

Los tornados son más frecuentes durante la primavera y menos durante el invierno.[22]​ Ya que la primavera y el otoño son periodos de transición (de clima cálido a frío y viceversa) hay más posibilidades de que el aire frío se encuentre con aire cálido, lo que provoca que durante esas estaciones se experimenten picos de actividad.[75]​ No obstante, las condiciones adecuadas para su formación se pueden presentar en cualquier época del año. Los tornados también pueden generarse a partir del ojo "Ojo (ciclón)") de los ciclones tropicales que tocan tierra,[76]​ lo cual suele suceder en el otoño y a fines del verano.

La incidencia de los tornados depende altamente de la hora del día, debido a la radiación solar.[77]​ A nivel mundial, la mayoría de los tornados ocurren durante la tarde, entre las 3:00 p. m. y las 7:00 p. m. del tiempo local, siendo el punto más alto a las 5:00 p. m..[78]​[79]​[80]​[81]​ Sin embargo, los tornados destructivos pueden ocurrir a cualquier hora del día. El tornado de Gainesville de 1936"), uno de los tornados más devastadores de la historia, ocurrió a las tiempo local.[22]​.

Association with climate

There are areas such as the Mediterranean Sea that in turn increases the volume of humidity in the atmosphere. Increased humidity can cause an increase in the occurrence of tornadoes, particularly during the cold season.[82]​.

Some evidence suggests that the El Niño Southern Oscillation (ENSO) phenomenon is loosely related to changes in tornado activity; This varies depending on the season and region as well as depending on whether the ENSO phenomenon corresponds to that of El Niño or La Niña "La Niña (climate)").[83]​.

Climate changes can affect tornadoes through "teleconnections", such as changes in the jet stream and other major weather patterns. Although it is possible that global warming could affect tornado activity,[84] such an effect may not yet be identifiable due to its complexity, the nature of the storms, and database quality issues. Additionally, any effect would vary by region.[85]​

Weather forecasting is carried out regionally by many national and international agencies. For the most part, they are also responsible for predicting the conditions that favor the development of tornadoes.

In Australia, numerous storm warnings are provided by that nation's Bureau of Meteorology. The country is in the process of upgrading to use pulse Doppler radar systems, having reached its first goal of installing six new radars in July 2006.[86]​.

On the other hand, in the United Kingdom the Tornado and Storm Research Organization (TORRO) carries out experimental forecasts. The Met Office provides official forecasts for this country, while in the rest of Europe the ESTOFEX project (European Storm Forecast Experiment) provides weather forecasts about the probability of climate,[88]​ and the European Severe Storms Laboratory (ESSL) maintains a database of events.[89]​.

Likewise, in the United States, generalized weather predictions are made by the Storm Prediction Center, based in Norman, Oklahoma.[90] This center makes probabilistic and categorical predictions for the next three days regarding extreme weather, including tornadoes. There is also a more general forecast that covers the period from the fourth to the eighth day. Just before the time when it is expected to occur a severe weather threat, such as a tornado, the SPC sends several alerts regarding the phenomenon, in collaboration with the local offices of the National Weather Service "National Weather Service (United States)") of that country.

In turn, in Japan the prediction and study of tornadoes is carried out by the Japan Meteorological Agency,[91]​ while in Canada weather warnings and forecasts, including those for tornadoes, are provided by seven regional offices of the Meteorological Service of Canada, a subdivision of Environment Canada.[92]​.

Rigurosos intentos para poder advertir los tornados comenzaron en los Estados Unidos a mediados del siglo . Antes de los años 1950, el único método para detectar un tornado era que alguien lo viera. Generalmente, la noticia de un tornado no llegaría a una estación climática local hasta después de la tormenta. No obstante, con el advenimiento del radar meteorológico, las zonas cercanas a las estaciones climáticas tendrían avisos con tiempo del mal clima. Los primeros avisos públicos de tornados aparecieron en 1950 y las primeras alertas de tornados, en 1952. En 1953 se confirmó que los ecos en cadena se encuentran asociados con los tornados.[93]​ Al reconocer estos patrones, los meteorólogos, estando a varios kilómetros de distancia, pudieron detectar tormentas que probablemente producirían tornados.[94]​.

Radar

Today, most developed countries have a network of weather radars, and this is still the main method of detecting possible tornadoes. Pulse Doppler radar stations are used in the United States and some other countries. These devices measure the speed and radial direction (whether they are approaching or moving away from the radar) of a storm's winds, and can thus detect evidence of rotation in storms that are more than 150 km away. When storms are far from a radar, only the upper parts of the storm are observed and important low areas are not recorded.[95] The resolution of the data also decreases with the distance between the storm and the radar. Some weather conditions that lead to tornadogenesis are not immediately detectable via radar and sometimes tornado development can occur more quickly than a radar can complete a scan and send the information. Additionally, most populated regions on Earth are now visible from the Geostationary Operational Environmental Satellite (GOES), which assists in forecasting tornadic storms.[96]​.

Storm Location

In the mid-1970s, the U.S. National Weather Service (NWS) increased its efforts to train individuals to spot storms and identify their main characteristics, such as heavy hail, devastating winds, and tornadoes, as well as the damage they cause. The program was called Skywarn"), and those who participated in it were local deputy sheriffs, state troopers, firefighters, ambulance drivers, radio operators, civil protection workers, storm chasers and ordinary citizens. When bad weather is expected, local weather stations request that these storm locators make the necessary searches and report any tornadoes immediately, so that the office can send a timely warning to the population.

Locators are typically trained by the NWS on behalf of, and report to, their respective organizations. Organizations activate public alarm systems such as sirens and the Emergency Alert System), and direct their report to the NWS.[97]​ There are more than 230,000 weather locators trained through Skywarn in the United States.[98]​.

In Canada, a similar network of volunteer weather locators, called Canwarn"), helps locate bad weather, with more than 1,000 volunteers.[96]​ In Europe, several nations are organizing localizer networks under the auspices of Skywarn Europe"),[99]​ and the Tornado and Storm Research Organization") (TORRO) has maintained a localizer network in the United Kingdom since 1974.[100]​.

Storm spotters are necessary because radar systems like NEXRAD cannot detect a tornado, only indications suggesting its presence. Radars can give warning before there is visual evidence of a tornado, but information from a spotter can confirm the threat or determine that a tornado's arrival is not imminent. Radar, when traveling in a straight line, progressively increases its altitude with respect to the ground as it moves away from the radar due to the curvature of the Earth, in addition to the fact that the signal also disperses.[95]​.

Storm spotters are trained to discern whether or not a storm seen at a certain distance is a supercell. They generally look at its rear, the main region of updrafts and inflow. Below the updraft there is a rainless base, and in the next step of tornadogenesis a rotating wall cloud forms. The vast majority of intense tornadoes occur with a wall cloud behind a supercell.[64]​.

The evidence that this is a supercell comes from the shape and structure of the storm, and other characteristics of cumulonimbus such as a vigorous column of updrafts, an emerging top above the cloud base that persists for a long time, a firm base, and a corkscrew appearance. Below the storm and closer to where most tornadoes are found, evidence of a supercell and the possibility of a tornado includes inflow bands (particularly curved), the strength of the inflow, the temperature and humidity of the incoming air, what the ratio of air entering and leaving the storm is, and how far the leading flank precipitation core and wall cloud are from each other. Tornadogenesis is most likely at the interface of the updraft and rear flank downdraft, and requires a balance between inflow and outflow.[15]​.

Rotating wall clouds, which generate tornadoes, generally precede them by five to thirty minutes. Rotating wall clouds are the visual manifestation of a mesocyclone. Unless occurring at a low level, tornadogenesis is highly unlikely unless a rear flank downdraft occurs, which is usually visibly evidenced by the evaporation of a cloud adjacent to the corner of a wall cloud. A tornado usually occurs when this happens or shortly after; First, a funnel cloud descends to the surface and in almost all cases, by the time it is halfway there, a surface eddy has already developed, meaning a tornado is on the ground before condensation connects the surface circulation to the storm. Tornadoes can also occur without wall clouds, under flanking lines. Locators look at all parts of a storm, as well as the cloud base and surface.[103]​.

The most extreme tornado on record was the Tri-State Tornado, which passed through parts of Missouri, Illinois, and Indiana on March 18, 1925. It likely would have been classified as an F5 tornado, although tornadoes were not classified at the time. It holds the records for having traveled the longest distance (352 km), the longest duration (about 3.5 hours) and the highest forward speed for a major tornado (117 km/h) in the world. In addition, it is the deadliest tornado in the history of the United States (695 deaths).[22] It was also at the time the second costliest tornado in history, but it has already been surpassed by many other unstandardized ones. When costs are normalized for wealth and inflation, it remains the third costliest tornado today.[104]​ The deadliest tornado globally was the Daulatpur-Saturia tornado in Bangladesh on April 26, 1989, which killed approximately 1,300 people.[105]​ Bangladesh has had at least 19 tornadoes in its history that have killed more than 100 people, which is It represents at least half of the total in the rest of the world.

Most of the records set for tornado outbreaks correspond to the so-called *Super Outbreak"), which affected a large part of the central United States and a small area of ​​southern Ontario in Canada between April 3 and 4, 1974. Not only did this outbreak feature an incredible 148 tornadoes in just 18 hours, but several of them were also violent; seven were of F5 intensity and twenty-three were F4. This The surge had sixteen tornadoes on the surface at the same time at its strongest. More than 300 people, possibly as many as 330, died from the tornadoes in this surge.[106]

Although it is almost impossible to directly measure the wind speed of the most violent tornado (conventional anemometers would be destroyed by strong winds), some tornadoes have been scanned by mobile Doppler radar units, which can provide an accurate estimate of a tornado's wind speed. The highest speed measured in a tornado, which is also the highest wind speed ever measured on the planet, is 484 ± 32 km/h in the Moore F5 tornado "Moore (Oklahoma)"), Oklahoma. Although the measurement was taken about 30 m above the surface, it demonstrates the power of the strongest tornadoes.[107]​.

Outside the United States there have also been significant waves of tornadoes. Other areas that are very active in terms of extreme weather have recorded significant tornado events, such as Northern Europe and central and southern South America. One of the most important waves of tornadoes worldwide is "Tragic Tuesday the 13th", named by meteorologists and fans in Argentina, the most important wave of tornadoes on record outside the United States; During the night of April 13, 1993, around three hundred tornadoes with intensities between F0 and F3 were recorded in the province of Buenos Aires, Argentina. Another significant tornado outbreak was the so-called "USSR Tornado Wave" of 1984, in which a category F4 tornado was recorded in Ivanovo, Russia (then part of the Soviet Union).

Storms that produce tornadoes can have intense updrafts, sometimes exceeding 240 km/h. Debris kicked up by a tornado can reach the main storm and be carried a long distance. A tornado that affected Great Bend, Kansas in November 1915 was an extreme case, where a "debris shower" occurred 80 miles from town, a sack of flour was found 117 miles away, and a canceled check from the Bank of Great Bend was found in a field outside Palmyra, Nebraska 300 miles to the northeast.[108] The waterspouts Sea waves and tornadoes have been used as a possible explanation for occasions when it has rained fish and other animals.[109]​.

A pesar de que los tornados pueden atacar en cualquier instante, existen precauciones y medidas preventivas que la gente puede adoptar para aumentar sus posibilidades de sobrevivir a un tornado. Autoridades como el Storm Prediction Center aconsejan contar con un plan contra tornados. Tras ser emitida una alerta de tornado, se debe buscar refugio en un sótano o en una habitación localizada en la parte más interna de una casa resistente ya que esto aumenta en gran medida las posibilidades de sobrevivir.[110]​ En áreas propensas a tornados, muchos edificios cuentan con refugios especiales para tormentas. Estas habitaciones subterráneas han ayudado a salvar miles de vidas.[111]​.

Algunos países cuentan con agencias meteorológicas que proporcionan predicciones de tornados e incrementan el nivel de alerta para un posible tornado (de la misma forma que lo hacen los avisos y alertas de tornados en Estados Unidos y Canadá). Las estaciones climatológicas de radio también proporcionan alarmas cuando se libera una advertencia por clima extremo para su área local, aunque este tipo de estaciones de radio se encuentran generalmente sólo en los Estados Unidos.

A menos que el tornado esté a gran distancia y sea visible, los meteorólogos aconsejan a los conductores que estacionen sus vehículos fuera del camino (para no bloquear al tráfico de emergencia), y buscar un refugio seguro. Si no hay uno en las cercanías, colocarse en lo profundo de una zanja es la siguiente mejor opción.

Myths and misconceptions

One of the most persistent myths associated with tornadoes is that opening windows will reduce the damage caused by the tornado. Although there is a marked drop in atmospheric pressure inside a strong tornado, it is unlikely that the drop in pressure would be enough to cause the building to explode. Some research shows that opening windows can actually increase the severity of tornado damage. Regardless of the validity of this explosion theory, it is better to spend your time seeking shelter and not opening windows. A violent tornado, of any form, can destroy a house regardless of whether its windows are open or closed.[112][113]​.

Another common belief is that highway overpasses are suitable shelter from tornadoes. In contrast, an overpass is a dangerous place to take shelter.[114] In the 1999 Oklahoma tornado outbreak on May 3, 1999, three freeway overpasses were struck by tornadoes, and at each of those three locations there was one death, along with many serious injuries. The area under the overpasses is believed to cause a wind tunnel effect, where the wind speed of the tornado and debris is increased. By comparison, during the same wave of tornadoes, more than 2,000 homes were completely destroyed, with another 7,000 damaged, and even then only a few dozen people died in their homes.[114]

An old belief is that the corner of a basement that is closest to the southwest provides the most protection during a tornado. The safest place, actually, is the end or corner of an underground room opposite the direction in which the tornado is moving (usually the northeast corner), or a room that is not underground but is as far inside your property as possible. Taking shelter under a sturdy table, in a basement, or under a ladder increases your chances of survival even further.[112]​[113]​.

Finally, there are areas where people believe they are protected from tornadoes, either by a large river, hill or mountain, or even by supernatural forces.[116] Tornadoes have been known to cross large rivers, climb mountains and affect valleys.[117] As a general rule, there is no area that is "safe" from tornadoes, although there are areas that are more susceptible than others, although the exception is in places surrounded by mountains.[112][113]​.

Meteorology is a relatively young science and the study of tornadoes even more so. Although they have been studied since the century and with greater emphasis since the middle of the century, there are still aspects of them that are a mystery.[118]​ Scientists have a fairly precise idea of ​​the development of storms and mesocyclones,[119]​[120]​ and the meteorological conditions that lead to their formation; However, the transition from supercell (or other formative processes) to tornadogenesis and the differentiation of tornadic and non-tornadic mesocyclones are aspects that are still not fully understood and are the focus of much of the research.[75]​.

Mesocyclones at the low levels of the atmosphere and the widening of the vorticity at the low levels that becomes the tornado are also being studied,[75]​ mainly what the processes are and what the relationship between the medium and the convective storm is. Intense tornadoes have been observed forming simultaneously with a mesocyclone above (instead of successive mesocyclone) and some intense tornadoes have occurred without a mid-level mesocyclone. In particular, the role of downdrafts, mainly the backflank downdraft, and the role of baroclinic boundaries, are important topics of study.[121]​.

Reliably predicting tornado intensity and longevity continues to be a problem, as do details concerning the characteristics of a tornado during its life cycle and tornadolysis. Other research topics of significance include tornadoes associated with mesovortices within linear storm structures and within tropical cyclones.[122]

Scientists still do not know the exact mechanisms by which most tornadoes form, and occasionally some still appear without a prior tornado warning.[123] Analyzes of observations from both stationary and mobile, surface and airborne, and remote and in situ instruments generate new ideas and refine existing notions. The use of mathematical models also provides greater understanding as new observations and discoveries are integrated into our physical understanding and then tested through computer simulations that validate the new notions while producing entirely new theoretical discoveries, many of which would otherwise be almost indeducible. Likewise, the development of new forms of observation and the installation of finer spatial and temporal observation networks have helped to have greater understanding and better predictions.[124]​.

Research programs, including study projects such as the VOTEX project), the deployment of TOTO, the Doppler On Wheels (DOW) and dozens of other programs, hope to answer many of the questions that still plague meteorologists. highlighting in this sense the National Science Foundation.[101][125]​.

• - Cyclone.

• - Natural disaster.

• - Extreme weather.

• - Whirlwind (meteorology) "Whirlwind (meteorology)").

• - Córdoba Tornado.

• - Delimited weak echo region.

• - Radius of maximum winds.

• - Wikimedia Commons hosts a multimedia category on Tornado.

• - Wiktionary has definitions and other information about tornado.

• - Database of severe weather events in Europe.

• - NOAA storm database 1950-present.

• - NOAA Tornado Preventive Guide.

The word "tornado" is a loanword "Loan (linguistics)") from English, which it arrived from the Spanish "tronada", which, according to the RAE, refers to a "thunderstorm".[10]​ The metathesis is undoubtedly due to a reinterpretation of the word under the influence of "tornar".[11]​[12]​.

Contenido

Un tornado se define en el Glossary of Meteorology como «una columna de aire que gira violentamente sobre sí misma, estando en contacto con el suelo, ya sea colgando de o debajo de una nube cumuliforme, y frecuentemente (pero no siempre) visible como una nube embudo...».[13]​ En la práctica, para que un vórtice sea clasificado como un tornado, debe tener contacto tanto con el suelo como con la base de la nube. Sin embargo, los científicos aún no han formulado una definición completa del término; por ejemplo, hay desacuerdos respecto a si múltiples puntos de contacto con el suelo provenientes del mismo embudo constituyen diferentes tornados.[14]​ El término «tornado» se refiere además al vórtice de viento, no a la nube de condensación.[15]​[16]​.

funnel cloud

A tornado is not necessarily visible; However, the low atmospheric pressure inside it and caused by the high wind speed - in accordance with Bernoulli's principle - as well as its rapid rotation (due to cyclostrophic equilibrium) generally cause the water vapor in the air to become visible by condensing in the form of water droplets, taking the form of a funnel cloud or a condensation funnel.[17] When a funnel cloud extends at least half the distance between the ground and the base of the cloud—which is usually less than two kilometers—[18]​ is considered a tornado.[19]​.

There is some disagreement over the definition of “funnel cloud” and “condensation funnel.” According to the Glossary of Meteorology, a funnel cloud is any rotating cloud hanging from a cumulus or cumulonimbus cloud, and therefore most tornadoes fall under this definition.[20] Among many meteorologists, a funnel cloud is defined strictly as a rotating cloud not associated with strong surface winds, and a "condensation funnel" is a term used for any cloud that is rotating beneath a cloud. cumuliform.[14]​.

Tornadoes often start out as funnel clouds without strong surface winds, however, not all of them turn into a tornado. Either way, many tornadoes are preceded by a funnel cloud. Most of them produce strong winds at the surface, while the visible funnel remains far from the ground, making it difficult to distinguish the difference between a funnel cloud and a tornado from a distance.[14]​.

Families and waves

Occasionally, a single storm produces more than one tornado, either simultaneously or in succession. Multiple tornadoes produced by the same storm are known together as a tornado family.[21]​.

Sometimes multiple tornadoes spawn from the same storm system. If its activity is not interrupted, this is considered a tornado surge, although there are several definitions. A period spanning several consecutive days with tornado surges in the same area (generated by multiple weather systems) is a tornado surge sequence, also known as an extended tornado surge.[13]​[22]​[23]​.

Shape and dimensions

Most tornadoes take the shape of a narrow funnel, a few hundred meters wide, with a small expansive cloud of debris near the ground, at least in their initial stage. Tornadoes can be completely obscured by rain or dust, and if so, they are particularly dangerous, since even experienced meteorologists may not see them.

Tornadoes, however, can come in many shapes and sizes. Small and relatively faint landspouts, for example, cannot be seen as anything more than a small whirlwind of dust on the ground. Although the condensation funnel may not extend from the ground, if the associated winds at the surface exceed 40 mph (64 km/h), the circulation is considered a tornado.[15] A tornado with a nearly cylindrical shape and relatively low height is sometimes called a stovepipe tornado.[24] Large tornadoes with a single vortex can be seen as huge buried wedges. on the ground, and are therefore known as "wedge tornadoes."[25] One of these tornadoes can be so wide that it appears to be a group of dark clouds, being even wider than the distance between the cloud base and the ground. Even experienced storm spotters may have difficulty differentiating a wedge tornado and a low cloud in the distance. Many, but not all, of the largest tornadoes are wedge-shaped.[26]​.

Tornadoes in their dissipating stage may look like narrow tubes or ropes, and they often curl or twist into complex shapes. These tornadoes are said to be in their "string phase," or becoming a "string tornado." When they take this shape, the length of their funnel increases, forcing the winds within the funnel to weaken due to conservation of angular momentum.[27] Tornadoes with multiple vortices, for their part, may appear to be a family of eddies rotating around a common center, or they may be completely obscured by condensation, dust, and debris, appearing to be a single funnel.[28]​

In the United States, on average tornadoes are about 150 m wide and travel about 8 km in contact with the ground. Either way, there is a wide range of tornado sizes. Weak tornadoes, or strong dissipating tornadoes, can be extremely narrow, sometimes only a few meters wide. A tornado was once reported to have a destruction zone only 2 m wide. On the other hand, wedge tornadoes can have a destruction zone 1.5 km wide, or even more. A tornado that hit Hallam "Hallam (Nebraska)", Nebraska, on May 22, 2004, was at one point measuring 4 km wide at ground level.[29]​.

In terms of path length, the 1925 Tri-State Tornado, which affected parts of Missouri, Illinois, and Indiana on March 18, 1925, officially touched the ground continuously for 220 miles (352 km). Many tornadoes that appear to have paths of 100 miles or more are actually a family of tornadoes that formed in rapid succession; However, there is no concrete evidence that this occurred in the case of the Tri-State Tornado.[22]​.

Appearance

Tornadoes can come in a wide variety of colors, depending on the environment in which they form. Those that develop in a dry environment can be practically invisible, barely distinguishable only thanks to the debris circulating at the base of the funnel. Condensation funnels that lift little or no debris may be gray or white. When traveling over a body of water, as waterspouts do, they can turn very white or even blue. Funnels that move slowly, consuming large amounts of debris and soil, are generally darker, taking on the color of the debris. Meanwhile, tornadoes in the Great Plains can turn red due to the reddish tint of the earth, and tornadoes in mountainous areas can travel over snow-covered terrain, turning bright white.

An important factor that determines the appearance of a tornado is lighting conditions. A tornado that is being lit from behind (seen with the sun behind it) looks very dark. The same tornado, seen with the sun behind the observer, may appear gray or bright white. Tornadoes that form during sunset can be many different colors, featuring shades of yellow, orange, and pink.[32]​.

Some factors that can reduce the visibility of tornadoes are dust raised by the storm's winds, heavy rain or hail, and darkness of night. Tornadoes that occur under these conditions are particularly dangerous, since only observations from weather radar, or possibly the noise they produce as they approach, serve as a warning to those in their path. In any case, most strong tornadoes form on the base of the storm's updraft, which is free of rain,[33]​ allowing them to be visible.[34]​ Additionally, most tornadoes occur during the afternoon, when the sun can penetrate even the densest clouds.[22]​ Likewise, nighttime tornadoes are generally illuminated due to the frequent appearance of lightning.

There is evidence, including images from mobile Doppler on Wheels radars) and witness reports, that most tornadoes have a clear, calm center where the pressure is extremely low, similar to the "Eye (cyclone)" of tropical cyclones. This area would be clear (possibly dusty), with relatively calm winds, and would be very dark, as the light would be blocked by debris spinning on the outside of the tornado. Those who claim to have seen They say they have achieved the inside of a tornado thanks to the illumination of lightning.[35][36][37]​.

Rotation

Tornadoes are formed by two types of vertical air movements: one anticyclonic with clockwise rotation, formed by cold, dry air that descends, decreasing its radius and therefore increasing its speed of rotation and becoming visible when it reaches the ground (due to the cloud of dust, leaves and other objects) and another ascending one, which constitutes a cyclonic area, whose radius of action increases in a spiral as it ascends counterclockwise in the northern hemisphere, and clockwise in the northern hemisphere. the southern hemisphere. Contrary to what happens with the type of descending anticyclonic funnel, as the hot air rises it widens, losing speed and, obviously, energy. Supercells and tornadoes rotate cyclonically in numerical simulations even when the Coriolis effect is ignored[38]​[39]​ Low-level tornadoes and mesocyclones owe their rotation to complex processes within the supercell and the environment.[40]​ This is the phase of the tornado that is easily visible, since as its height increases and cools, the water vapor it contains condenses in the rising air column, forming a funnel cloud that increases its diameter as it rises although, in return, its rotation speed also decreases.

No obstante lo que se ha indicado, tanto la rotación ascendente hacia la izquierda en el hemisferio norte como la descendente hacia la derecha también en el hemisferio norte, así como la formación de los tornados tipo cuerda y su desplazamiento en su trayectoria superficial se deben al efecto de Coriolis. Ello se debe a la gran dimensión vertical de los tornados, en comparación con su anchura en la superficie: la velocidad de rotación terrestre a los 30° de latitud es de 404 m/s como señala Antonio Gil Olcina.[41]​ Como resulta lógico, esta velocidad genera un efecto intenso en la superficie, donde la fricción hace girar la columna de aire hacia la derecha (de nuevo en el hemisferio norte) mientras que en altura, dicha velocidad es mucho menor al tener la columna o embudo un diámetro mucho mayor.

Todos los tornados comienzan girando en dirección anticiclónica y están formados por una corriente vertical de aire frío y seco que desciende en forma de una espiral que va disminuyendo su radio de giro al ir bajando, con lo que aumenta considerablemente su velocidad de rotación y da origen en compensación, a una espiral ascendente de aire caliente y seco pero que forma rápidamente una nube embudo al enfriarse rápidamente ese aire girando de manera ciclónica, es decir, antihoraria en el hemisferio norte y horaria en el hemisferio sur (mirando desde arriba). La existencia de dos torbellinos simultáneos girando en sentido opuesto en el mismo punto es lo que explica la asimetría de un tornado: siempre tiene una parte abierta, sin nube de condensación a baja altura (por donde desciende el aire frío y seco) y otra por donde asciende el aire caliente y húmedo que, finalmente, puede alcanzar la nube formando una nube embudo por el aumento del diámetro de giro. Generalmente, sólo sistemas tan débiles como las trombas terrestres, los remolinos de arena y los gustnados pueden rotar anticiclónicamente, y usualmente sólo lo hacen aquellos que se forman en el lado anticiclónico de la corriente descendente del flanco trasero") en una supercelda ciclónica.[42]​ No obstante, en raros casos, los tornados anticiclónicos se forman en asociación con el mesoanticiclón") de una supercélula anticiclónica —de la misma forma que un típico tornado ciclónico— o como un tornado acompañante, ya sea como un tornado satélite o asociado con circulaciones anticiclónicas dentro de una supercelda.[43]​.

Sound and seismology

The sounds produced by a tornado are caused by multiple mechanisms. Various sounds produced by tornadoes have been reported over time, often compared to sounds familiar to witnesses and generally as some variation of a roar. Frequently reported sounds include a freight train, rapids or waterfalls, a jet engine, or combinations of these. Many tornadoes are not audible at great distances; The nature and distance of sound propagation depends on atmospheric conditions and topography.

Winds from the tornado vortex and turbulent constituent eddies, as well as the interaction of air currents with the surface and debris, contribute to the creation of sounds. Funnel clouds also make sounds. [44]

Since many tornadoes are audible only when they are very close, noise is not a reliable warning of a tornado. Additionally, any strong wind, even heavy hail or the continuous thunder of lightning in a thunderstorm, can produce a roar similar to that of tornadoes.[45]​.

Tornadoes also produce inaudible infrasonic signatures.[46] Unlike audible signatures, inaudible signatures from tornadoes have been isolated; Due to the long-distance propagation of low-frequency sound waves, attempts are being made to develop devices for the prediction and detection of tornadoes that also serve to understand their morphology, dynamics and formation.[47]​ Tornadoes also produce a detectable seismic signature, and research continues to isolate it and understand its process.[48]​.

Electromagnetism, lightning and other effects

Tornadoes emit in the electromagnetic spectrum, and emissions of atmospheric radio and electric field signals have been detected.[47][49][50] Correlations between tornadoes and patterns of lightning activity have also been observed. Tornadic storms do not contain more lightning than other storms, and some tornadic cells never produce lightning. Generally, cloud-to-ground (cloud-to-ground) lightning activity It decreases when a tornado reaches the surface and returns to its normal level when the tornado dissipates. In many cases, tornadoes and thunderstorms of great intensity exhibit an increase and anomalous dominance of positive polarity in the CG discharges.

The presence of luminosity has been reported in the past, and is likely due to confusion in identifications with external light sources such as lightning, urban lights, and flashes from damaged electrical installations, since internal sources are rarely reported and are not known to have been documented. In addition to winds, tornadoes also present changes in atmospheric variables such as temperature, humidity and pressure. For example, on June 24, 2003, near Manchester, South Dakota, an investigation recorded a pressure deficit of 100 mbar "Bar (unit of pressure)"). The pressure gradually decreased as the vortex approached and then dropped extremely rapidly to 850 mbar at the center of the violent tornado before increasing rapidly as the vortex moved away, resulting in a "V"-shaped pressure graph. At the same time, the temperature tends to decrease and the moisture content to increase in the vicinity of a tornado.[52]​.

Relationship with the supercell

Many tornadoes develop from a type of storm known as supercells.[53] Supercells contain mesocyclones, which are an area of ​​organized rotation of air located in the atmosphere, between 2 and 10 km wide. In addition to tornadoes, heavy rain, lightning, strong gusts of wind, and hail are common in such storms. While most tornadoes, particularly the strongest ones (EF3 to EF5 on the Fujita-Pearson Scale), are derived from supercells, some can also form from other air circulations, and are therefore called non-supercell tornadoes. These types of tornadoes, however, tend to be of lower intensity.[54]​.

Training

Most tornadoes originating in supercells follow a recognizable life cycle. This begins with the origin of the supercell itself, which occurs when a current of cold, dry air descends from the top of a cloud (generally, from the back) to compensate for the warm air that rises from the front to increase the dimensions of the cloud itself. As the cold air is heavier, layers of unstable air are produced where the cold air descends and forces the warm air to rise, creating the storm. If the temperature differences are large enough, the descent of cold air can occur in the form of a vortex, invisible because it is dry air: it becomes visible when, upon reaching the ground, it begins to raise dust, leaves and other objects. This descending air, called the rear flank downdraft (RFD), accelerates as it approaches the ground, and drags the supercell mesocyclone towards it.[15]​ The updrafts, for their part, attract the air around them, increasing the rotation and becoming a narrow column, known as a funnel cloud, which increases in diameter and decreases in spin speed as it rises.[54]​.

When a column of cold, dry air descends with an anticyclonic gyre, that is, with a clockwise rotation (coming from the top of a vertically developing cloud) towards the ground due to the greater density of the cold air, a condensation funnel begins to form (visible by the condensation of humid air as it ascends) in the opposite direction (that is, cyclonic), which compensates for the loss of cloud mass that previously descended, forming the rotating wall cloud. As the anticyclonic funnel descends (RFD) and reach the ground, it creates a gust front") that can cause damage a good distance from the tornado. Usually, the funnel cloud develops into a tornado very soon after the RFD hits the ground.[15]​.

Maturity

Initially, the tornado has a good source of warm, moist air entering it to give it energy, so it grows until it reaches its mature stage. This can last a few minutes or more than an hour, and it is during this time that the tornado generally causes the most damage and its dimensions reach their maximum, measuring in some cases more than 1.5 km wide. Meanwhile, the RFD, which at this stage is an area of ​​cold surface winds, begins to settle around the tornado, disrupting the flow of warm air that feeds it.[15]​.

Dissipation

When the RFD completely envelops the tornado and cuts off its air supply, the vortex begins to weaken, becoming thin, rope-like. This is the dissipation phase, which normally lasts no more than a few minutes, after which the tornado fades away. During this stage the shape of the tornado depends largely on the winds of the main storm, which can cause it to take unusual shapes.[22]​[31][32]​ Even though the tornado is disappearing, it is still capable of causing damage. By becoming a thin tube, in the same way that a skater draws in his arms to spin faster, the winds can increase their speed at this point.[15]​.

With the tornado entering its dissipation stage, its associated mesocyclone usually also weakens, also because the RFD cuts off the airflow that feeds it. As the first mesocyclone and its associated tornado dissipate, the storm flow may concentrate in a new area closer to its center. If a new mesocyclone forms, the cycle can repeat, producing one or more new tornadoes. Occasionally, the old and new mesocyclones produce tornadoes at the same time.

Although this theory of how tornadoes arise, develop, and disappear is widely accepted, it does not explain the formation of smaller tornadoes, such as landspouts or tornadoes with multiple vortices. All of them have different mechanisms that influence their development, however, most follow a pattern similar to the one described here.[55]​.

real tornadoes

A multiple vortex tornado or multivortex tornado is a type of tornado in which two or more columns of moving air rotate around a common center. Multivortex structures can occur in almost any air circulation, but are frequently observed in intense tornadoes. These vortices generally create small areas that cause greater damage along the path of the main tornado.[14] This phenomenon is different from the satellite tornado, which is a weaker tornado that forms very close to another larger, stronger tornado, contained within the same mesocyclone. The satellite tornado appears to "orbit" around the larger tornado (hence the name), resembling a multivortex tornado. However, the satellite tornado is a different circulation, and is much smaller than the main funnel.[14]​.

The waterspout or waterspout is simply a tornado that is over the water. However, researchers generally distinguish tornadic from non-tornadic waterspouts. Non-tornadic waterspouts are less strong but much more common, and are similar in their dynamics to so-called dust devils and landspouts. They form at the bases of cumulus congestus clouds in tropical and subtropical waters. They have relatively weak winds, smooth walls with laminar flow, and generally travel very slowly, if at all. They commonly occur in the Florida Keys, the Río de la Plata, the Paraná River, and the northern Adriatic Sea.[56][57][58] In contrast, tornadic waterspouts are literally "tornadoes over water." They form over it in a similar way to mesocyclonic tornadoes, or they are land tornadoes that reach the water. Since they form from strong storms and can be much more intense, faster and longer lasting than non-tornadic waterspouts, they are considered more dangerous.[59]​.

A landspout, also called a non-supercellular tornado, tornado or funnel cloud, or landspout, is a tornado that is not associated with a mesocyclone. Its name comes from its name as a "non-tornadic waterspout over land." Waterspouts and landspouts share several distinctive characteristics, including their relative weakness, short duration, and a small, smooth condensation funnel that often does not touch the ground. These tornadoes also create a distinctive laminar cloud of dust when they make contact with the ground, because their mechanics are different from those of mesoform tornadoes. Although they are generally weaker than classic tornadoes, they can produce strong winds that are still capable of causing serious damage.[14]​[15]​.

Tornado-like circulations

A gustnado is a small vertical eddy associated with a gust front or downburst. Since they are not technically connected to the base of a cloud, there is some debate about whether gustnadoes are tornadoes. They form when a flow of cold, dry, fast air from a thunderstorm encounters a mass of warm, moist, stationary air near the boundary of the flow, resulting in a “rounding” effect (exemplified by a rolling cloud). If the wind shear at lower levels is strong enough, the rotation can become horizontal or diagonal and make contact with the ground. The result is a taste.[14]​[60]​.

A dust devil or sand and dust devil, known in English as a dust devil (literally translated as "dust devil"), resembles a tornado in that it is a rotating vertical column of air. However, they form under clear skies and rarely reach the strength of weaker tornadoes. They develop when a strong downward current of air "Subsidence (meteorology)") reaches the ground, causing a clockwise whirlpool (again, in the northern hemisphere) that raises dust, leaves and other objects, potentially causing minor or medium damage to homes and other infrastructure works. The fact that they form on clear days is sufficient proof of the anticyclonic nature of this phenomenon. The clear atmosphere indicates meteorological stability (no clouds, as can be seen in both images). What happens is that the contact of the descending cold air with the ground that is very hot due to solar radiation automatically generates a heating of that cold air, with the consequent convection process and which usually also cools down very quickly upon reaching a certain height. It corresponds to those days at the beginning of spring when the air temperature is quite cold but the solar radiation is very intense. In both the image on the left and in the video on the right you can see the characteristics of a dust devil: clear skies and rotation or clockwise rotation (anticyclonic), that is, from left to right because it is in the northern hemisphere. This type of spin is evident in the case of the video and despite this evidence, the origin and dynamics of tornadoes have not yet been well understood, which, as is the case with all types of cyclones, consist of two columns of air, one descending or subsiding and the other ascending or convective. And all cyclonic phenomena have the same structure and the same development. The variations between one phenomenon and another (tornado, gustnado, dust devil, landspout, etc.) are matters of meteorological differences and their scale.

Those circulations that develop near forest fires are called fire whirlwinds or whirlwinds. They are not considered tornadoes except in the rare case that they connect to a pyrocumulus cloud or another cumuliform cloud above them. Fire whirls are generally not as strong as storm-related tornadoes. However, they can cause considerable damage.[22]​.

A steam devil is a term used to describe a rotating updraft involving steam or smoke. A steam whirl is very rare, but is formed primarily from smoke emitted from the chimneys of a power plant. Hot springs and deserts can also be suitable areas for the formation of a steam vortex. This phenomenon can occur over water, when cold arctic air meets relatively warm water.

The Fujita-Pearson Scale and the so-called Enhanced Fujita Scale classify tornadoes according to the damage caused. The enhanced scale (EF) was a refinement of the old Fujita scale, using wind estimates and better description of damage; However, it was designed so that a tornado rated on the Fujita scale would receive the same numerical rank, and was implemented beginning in the United States in 2007. An EF0 tornado, the weakest on the scale, is likely to damage trees but not structures, while an EF5 tornado, the strongest, can rip buildings from their foundations, leaving them exposed and even deforming skyscrapers. The similar TORRO scale ranges from T0 for extremely weak tornadoes to T11 for the most powerful tornadoes known. Data obtained from pulse Doppler radar, photogrammetry, and patterns on the ground (cycloidal signatures) can also be analyzed to determine intensity and give a range.[14]​[61][62]​.

Tornadoes vary in intensity regardless of their shape, size and location, although strong tornadoes are generally larger than weak ones. The relationship with the length of its path and duration also varies, although tornadoes with a longer path tend to be stronger.[63]​ In the case of violent tornadoes, they only present great intensity in a portion of the path, much of this intensity coming from subvortices.[22]​.

In the United States, 80% of tornadoes are classified as EF0 and EF1 (T0 to T3). The higher the intensity of a range, the lower its incidence rate, since less than 1% are violent tornadoes (EF4, T8 or stronger).[64]​ Outside of Tornado Alley, and North America in general, violent tornadoes are extremely rare. Apparently this is due more than anything to the lower number of tornadoes in general outside that region, since research shows that the distribution of tornadoes according to their intensity is quite similar worldwide. A few major tornadoes occur each year in Europe, areas of south-central Asia, portions of southeastern South America, and southern Africa.[65]​.

En los Estados Unidos se presentan más tornados que en cualquier otro país: unas cuatro veces más que los que se estima que se forman en toda Europa, sin incluir trombas marinas.[66]​ Esto se debe principalmente a la geografía única del continente americano. América del Norte es relativamente grande y se extiende desde la zona intertropical hasta las áreas árticas, y no cuenta con una cadena montañosa importante que vaya de este a oeste y que bloquee el flujo de aire entre estas dos zonas. En las latitudes centrales, donde ocurren la mayor parte de los tornados, las Montañas Rocosas bloquean la humedad y el flujo atmosférico, permitiendo que exista aire más seco en los niveles intermedios de la tropósfera, y causando la formación de un área con presión baja al este de dichas montañas. Un incremento en el flujo de aire desde las Rocosas propicia la formación de una línea seca") cuando el flujo es fuerte en los niveles superiores,[67]​ mientras el golfo de México, al este, proporciona abundante humedad en los niveles bajos de la atmósfera. Esta topografía única provoca muchas colisiones de aire cálido con aire frío, que son las condiciones que crean tormentas fuertes y duraderas. Una gran parte de estos tornados se forman en dicha área del centro de los Estados Unidos entre las Rocosas y el golfo, conocida como Tornado Alley («callejón de los tornados»).[3]​ Esta área abarca también partes de Canadá, principalmente en Ontario y las praderas canadienses, aunque el sudeste de Quebec, el interior de Columbia Británica y el occidente de Nuevo Brunswick también son propensos a tornados.[68]​ En ocasiones también se presentan tornados fuertes en el noreste de México. En promedio, en los Estados Unidos ocurren unos 1200 tornados por año.

Fuera de EE. UU., los Países Bajos presentan el mayor número de tornados por área de cualquier país al registrarse allí más de 20 tornados, lo que equivale a 0.00048 tornados/km² anualmente, seguidos por el Reino Unido que presenta anualmente unos 33, es decir, 0.00013 tornados/km², mientras que en Argentina, se registran unos 30 por año, a lo que va 0.0009 tornados/km², mayormente en la zona de llanuras comprendida por el área central y norte de la provincia de Buenos Aires, Córdoba "Provincia de Córdoba (Argentina)"), Santa Fe, Entre Ríos, Santiago del Estero, Chaco y Formosa, habiéndose registrado por ejemplo trombas marinas en la localidad de Mar del Tuyú.[69]​ En números absolutos, sin importar la extensión territorial;[70]​[71]​ de cualquier forma, la mayoría son pequeños y causan muy poco daño, el Reino Unido experimenta más tornados que cualquier país europeo, a la vez que Argentina representa la mayor cantidad de tornados que cualquier país latinoamericano, el segundo en América (detrás de Estados Unidos), y también del mundo incluyendo trombas marinas, en Argentina como también en el Reino Unido.[66]​.

Los tornados matan un promedio de 179 personas por año en Bangladés, por mucho la mayor cantidad dentro de un país en el mundo. Esto se debe a su elevada densidad de población, deficiente calidad de las construcciones, carencia de conocimientos acerca de medidas de seguridad para combatir a los tornados y otros factores.[72]​[73]​ Otros países del mundo que cuentan con tornados frecuentemente incluyen a Argentina, Sudáfrica, en Brasil en la frontera con Argentina, Australia y Nueva Zelanda, así como porciones de Europa y Asia.[6]​[74]​.

Los tornados son más frecuentes durante la primavera y menos durante el invierno.[22]​ Ya que la primavera y el otoño son periodos de transición (de clima cálido a frío y viceversa) hay más posibilidades de que el aire frío se encuentre con aire cálido, lo que provoca que durante esas estaciones se experimenten picos de actividad.[75]​ No obstante, las condiciones adecuadas para su formación se pueden presentar en cualquier época del año. Los tornados también pueden generarse a partir del ojo "Ojo (ciclón)") de los ciclones tropicales que tocan tierra,[76]​ lo cual suele suceder en el otoño y a fines del verano.

La incidencia de los tornados depende altamente de la hora del día, debido a la radiación solar.[77]​ A nivel mundial, la mayoría de los tornados ocurren durante la tarde, entre las 3:00 p. m. y las 7:00 p. m. del tiempo local, siendo el punto más alto a las 5:00 p. m..[78]​[79]​[80]​[81]​ Sin embargo, los tornados destructivos pueden ocurrir a cualquier hora del día. El tornado de Gainesville de 1936"), uno de los tornados más devastadores de la historia, ocurrió a las tiempo local.[22]​.

Association with climate

There are areas such as the Mediterranean Sea that in turn increases the volume of humidity in the atmosphere. Increased humidity can cause an increase in the occurrence of tornadoes, particularly during the cold season.[82]​.

Some evidence suggests that the El Niño Southern Oscillation (ENSO) phenomenon is loosely related to changes in tornado activity; This varies depending on the season and region as well as depending on whether the ENSO phenomenon corresponds to that of El Niño or La Niña "La Niña (climate)").[83]​.

Climate changes can affect tornadoes through "teleconnections", such as changes in the jet stream and other major weather patterns. Although it is possible that global warming could affect tornado activity,[84] such an effect may not yet be identifiable due to its complexity, the nature of the storms, and database quality issues. Additionally, any effect would vary by region.[85]​

Weather forecasting is carried out regionally by many national and international agencies. For the most part, they are also responsible for predicting the conditions that favor the development of tornadoes.

In Australia, numerous storm warnings are provided by that nation's Bureau of Meteorology. The country is in the process of upgrading to use pulse Doppler radar systems, having reached its first goal of installing six new radars in July 2006.[86]​.

On the other hand, in the United Kingdom the Tornado and Storm Research Organization (TORRO) carries out experimental forecasts. The Met Office provides official forecasts for this country, while in the rest of Europe the ESTOFEX project (European Storm Forecast Experiment) provides weather forecasts about the probability of climate,[88]​ and the European Severe Storms Laboratory (ESSL) maintains a database of events.[89]​.

Likewise, in the United States, generalized weather predictions are made by the Storm Prediction Center, based in Norman, Oklahoma.[90] This center makes probabilistic and categorical predictions for the next three days regarding extreme weather, including tornadoes. There is also a more general forecast that covers the period from the fourth to the eighth day. Just before the time when it is expected to occur a severe weather threat, such as a tornado, the SPC sends several alerts regarding the phenomenon, in collaboration with the local offices of the National Weather Service "National Weather Service (United States)") of that country.

In turn, in Japan the prediction and study of tornadoes is carried out by the Japan Meteorological Agency,[91]​ while in Canada weather warnings and forecasts, including those for tornadoes, are provided by seven regional offices of the Meteorological Service of Canada, a subdivision of Environment Canada.[92]​.

Rigurosos intentos para poder advertir los tornados comenzaron en los Estados Unidos a mediados del siglo . Antes de los años 1950, el único método para detectar un tornado era que alguien lo viera. Generalmente, la noticia de un tornado no llegaría a una estación climática local hasta después de la tormenta. No obstante, con el advenimiento del radar meteorológico, las zonas cercanas a las estaciones climáticas tendrían avisos con tiempo del mal clima. Los primeros avisos públicos de tornados aparecieron en 1950 y las primeras alertas de tornados, en 1952. En 1953 se confirmó que los ecos en cadena se encuentran asociados con los tornados.[93]​ Al reconocer estos patrones, los meteorólogos, estando a varios kilómetros de distancia, pudieron detectar tormentas que probablemente producirían tornados.[94]​.

Radar

Today, most developed countries have a network of weather radars, and this is still the main method of detecting possible tornadoes. Pulse Doppler radar stations are used in the United States and some other countries. These devices measure the speed and radial direction (whether they are approaching or moving away from the radar) of a storm's winds, and can thus detect evidence of rotation in storms that are more than 150 km away. When storms are far from a radar, only the upper parts of the storm are observed and important low areas are not recorded.[95] The resolution of the data also decreases with the distance between the storm and the radar. Some weather conditions that lead to tornadogenesis are not immediately detectable via radar and sometimes tornado development can occur more quickly than a radar can complete a scan and send the information. Additionally, most populated regions on Earth are now visible from the Geostationary Operational Environmental Satellite (GOES), which assists in forecasting tornadic storms.[96]​.

Storm Location

In the mid-1970s, the U.S. National Weather Service (NWS) increased its efforts to train individuals to spot storms and identify their main characteristics, such as heavy hail, devastating winds, and tornadoes, as well as the damage they cause. The program was called Skywarn"), and those who participated in it were local deputy sheriffs, state troopers, firefighters, ambulance drivers, radio operators, civil protection workers, storm chasers and ordinary citizens. When bad weather is expected, local weather stations request that these storm locators make the necessary searches and report any tornadoes immediately, so that the office can send a timely warning to the population.

Locators are typically trained by the NWS on behalf of, and report to, their respective organizations. Organizations activate public alarm systems such as sirens and the Emergency Alert System), and direct their report to the NWS.[97]​ There are more than 230,000 weather locators trained through Skywarn in the United States.[98]​.

In Canada, a similar network of volunteer weather locators, called Canwarn"), helps locate bad weather, with more than 1,000 volunteers.[96]​ In Europe, several nations are organizing localizer networks under the auspices of Skywarn Europe"),[99]​ and the Tornado and Storm Research Organization") (TORRO) has maintained a localizer network in the United Kingdom since 1974.[100]​.

Storm spotters are necessary because radar systems like NEXRAD cannot detect a tornado, only indications suggesting its presence. Radars can give warning before there is visual evidence of a tornado, but information from a spotter can confirm the threat or determine that a tornado's arrival is not imminent. Radar, when traveling in a straight line, progressively increases its altitude with respect to the ground as it moves away from the radar due to the curvature of the Earth, in addition to the fact that the signal also disperses.[95]​.

Storm spotters are trained to discern whether or not a storm seen at a certain distance is a supercell. They generally look at its rear, the main region of updrafts and inflow. Below the updraft there is a rainless base, and in the next step of tornadogenesis a rotating wall cloud forms. The vast majority of intense tornadoes occur with a wall cloud behind a supercell.[64]​.

The evidence that this is a supercell comes from the shape and structure of the storm, and other characteristics of cumulonimbus such as a vigorous column of updrafts, an emerging top above the cloud base that persists for a long time, a firm base, and a corkscrew appearance. Below the storm and closer to where most tornadoes are found, evidence of a supercell and the possibility of a tornado includes inflow bands (particularly curved), the strength of the inflow, the temperature and humidity of the incoming air, what the ratio of air entering and leaving the storm is, and how far the leading flank precipitation core and wall cloud are from each other. Tornadogenesis is most likely at the interface of the updraft and rear flank downdraft, and requires a balance between inflow and outflow.[15]​.

Rotating wall clouds, which generate tornadoes, generally precede them by five to thirty minutes. Rotating wall clouds are the visual manifestation of a mesocyclone. Unless occurring at a low level, tornadogenesis is highly unlikely unless a rear flank downdraft occurs, which is usually visibly evidenced by the evaporation of a cloud adjacent to the corner of a wall cloud. A tornado usually occurs when this happens or shortly after; First, a funnel cloud descends to the surface and in almost all cases, by the time it is halfway there, a surface eddy has already developed, meaning a tornado is on the ground before condensation connects the surface circulation to the storm. Tornadoes can also occur without wall clouds, under flanking lines. Locators look at all parts of a storm, as well as the cloud base and surface.[103]​.

The most extreme tornado on record was the Tri-State Tornado, which passed through parts of Missouri, Illinois, and Indiana on March 18, 1925. It likely would have been classified as an F5 tornado, although tornadoes were not classified at the time. It holds the records for having traveled the longest distance (352 km), the longest duration (about 3.5 hours) and the highest forward speed for a major tornado (117 km/h) in the world. In addition, it is the deadliest tornado in the history of the United States (695 deaths).[22] It was also at the time the second costliest tornado in history, but it has already been surpassed by many other unstandardized ones. When costs are normalized for wealth and inflation, it remains the third costliest tornado today.[104]​ The deadliest tornado globally was the Daulatpur-Saturia tornado in Bangladesh on April 26, 1989, which killed approximately 1,300 people.[105]​ Bangladesh has had at least 19 tornadoes in its history that have killed more than 100 people, which is It represents at least half of the total in the rest of the world.

Most of the records set for tornado outbreaks correspond to the so-called *Super Outbreak"), which affected a large part of the central United States and a small area of ​​southern Ontario in Canada between April 3 and 4, 1974. Not only did this outbreak feature an incredible 148 tornadoes in just 18 hours, but several of them were also violent; seven were of F5 intensity and twenty-three were F4. This The surge had sixteen tornadoes on the surface at the same time at its strongest. More than 300 people, possibly as many as 330, died from the tornadoes in this surge.[106]

Although it is almost impossible to directly measure the wind speed of the most violent tornado (conventional anemometers would be destroyed by strong winds), some tornadoes have been scanned by mobile Doppler radar units, which can provide an accurate estimate of a tornado's wind speed. The highest speed measured in a tornado, which is also the highest wind speed ever measured on the planet, is 484 ± 32 km/h in the Moore F5 tornado "Moore (Oklahoma)"), Oklahoma. Although the measurement was taken about 30 m above the surface, it demonstrates the power of the strongest tornadoes.[107]​.

Outside the United States there have also been significant waves of tornadoes. Other areas that are very active in terms of extreme weather have recorded significant tornado events, such as Northern Europe and central and southern South America. One of the most important waves of tornadoes worldwide is "Tragic Tuesday the 13th", named by meteorologists and fans in Argentina, the most important wave of tornadoes on record outside the United States; During the night of April 13, 1993, around three hundred tornadoes with intensities between F0 and F3 were recorded in the province of Buenos Aires, Argentina. Another significant tornado outbreak was the so-called "USSR Tornado Wave" of 1984, in which a category F4 tornado was recorded in Ivanovo, Russia (then part of the Soviet Union).

Storms that produce tornadoes can have intense updrafts, sometimes exceeding 240 km/h. Debris kicked up by a tornado can reach the main storm and be carried a long distance. A tornado that affected Great Bend, Kansas in November 1915 was an extreme case, where a "debris shower" occurred 80 miles from town, a sack of flour was found 117 miles away, and a canceled check from the Bank of Great Bend was found in a field outside Palmyra, Nebraska 300 miles to the northeast.[108] The waterspouts Sea waves and tornadoes have been used as a possible explanation for occasions when it has rained fish and other animals.[109]​.

A pesar de que los tornados pueden atacar en cualquier instante, existen precauciones y medidas preventivas que la gente puede adoptar para aumentar sus posibilidades de sobrevivir a un tornado. Autoridades como el Storm Prediction Center aconsejan contar con un plan contra tornados. Tras ser emitida una alerta de tornado, se debe buscar refugio en un sótano o en una habitación localizada en la parte más interna de una casa resistente ya que esto aumenta en gran medida las posibilidades de sobrevivir.[110]​ En áreas propensas a tornados, muchos edificios cuentan con refugios especiales para tormentas. Estas habitaciones subterráneas han ayudado a salvar miles de vidas.[111]​.

Algunos países cuentan con agencias meteorológicas que proporcionan predicciones de tornados e incrementan el nivel de alerta para un posible tornado (de la misma forma que lo hacen los avisos y alertas de tornados en Estados Unidos y Canadá). Las estaciones climatológicas de radio también proporcionan alarmas cuando se libera una advertencia por clima extremo para su área local, aunque este tipo de estaciones de radio se encuentran generalmente sólo en los Estados Unidos.

A menos que el tornado esté a gran distancia y sea visible, los meteorólogos aconsejan a los conductores que estacionen sus vehículos fuera del camino (para no bloquear al tráfico de emergencia), y buscar un refugio seguro. Si no hay uno en las cercanías, colocarse en lo profundo de una zanja es la siguiente mejor opción.

Myths and misconceptions

One of the most persistent myths associated with tornadoes is that opening windows will reduce the damage caused by the tornado. Although there is a marked drop in atmospheric pressure inside a strong tornado, it is unlikely that the drop in pressure would be enough to cause the building to explode. Some research shows that opening windows can actually increase the severity of tornado damage. Regardless of the validity of this explosion theory, it is better to spend your time seeking shelter and not opening windows. A violent tornado, of any form, can destroy a house regardless of whether its windows are open or closed.[112][113]​.

Another common belief is that highway overpasses are suitable shelter from tornadoes. In contrast, an overpass is a dangerous place to take shelter.[114] In the 1999 Oklahoma tornado outbreak on May 3, 1999, three freeway overpasses were struck by tornadoes, and at each of those three locations there was one death, along with many serious injuries. The area under the overpasses is believed to cause a wind tunnel effect, where the wind speed of the tornado and debris is increased. By comparison, during the same wave of tornadoes, more than 2,000 homes were completely destroyed, with another 7,000 damaged, and even then only a few dozen people died in their homes.[114]

An old belief is that the corner of a basement that is closest to the southwest provides the most protection during a tornado. The safest place, actually, is the end or corner of an underground room opposite the direction in which the tornado is moving (usually the northeast corner), or a room that is not underground but is as far inside your property as possible. Taking shelter under a sturdy table, in a basement, or under a ladder increases your chances of survival even further.[112]​[113]​.

Finally, there are areas where people believe they are protected from tornadoes, either by a large river, hill or mountain, or even by supernatural forces.[116] Tornadoes have been known to cross large rivers, climb mountains and affect valleys.[117] As a general rule, there is no area that is "safe" from tornadoes, although there are areas that are more susceptible than others, although the exception is in places surrounded by mountains.[112][113]​.

Meteorology is a relatively young science and the study of tornadoes even more so. Although they have been studied since the century and with greater emphasis since the middle of the century, there are still aspects of them that are a mystery.[118]​ Scientists have a fairly precise idea of ​​the development of storms and mesocyclones,[119]​[120]​ and the meteorological conditions that lead to their formation; However, the transition from supercell (or other formative processes) to tornadogenesis and the differentiation of tornadic and non-tornadic mesocyclones are aspects that are still not fully understood and are the focus of much of the research.[75]​.

Mesocyclones at the low levels of the atmosphere and the widening of the vorticity at the low levels that becomes the tornado are also being studied,[75]​ mainly what the processes are and what the relationship between the medium and the convective storm is. Intense tornadoes have been observed forming simultaneously with a mesocyclone above (instead of successive mesocyclone) and some intense tornadoes have occurred without a mid-level mesocyclone. In particular, the role of downdrafts, mainly the backflank downdraft, and the role of baroclinic boundaries, are important topics of study.[121]​.

Reliably predicting tornado intensity and longevity continues to be a problem, as do details concerning the characteristics of a tornado during its life cycle and tornadolysis. Other research topics of significance include tornadoes associated with mesovortices within linear storm structures and within tropical cyclones.[122]

Scientists still do not know the exact mechanisms by which most tornadoes form, and occasionally some still appear without a prior tornado warning.[123] Analyzes of observations from both stationary and mobile, surface and airborne, and remote and in situ instruments generate new ideas and refine existing notions. The use of mathematical models also provides greater understanding as new observations and discoveries are integrated into our physical understanding and then tested through computer simulations that validate the new notions while producing entirely new theoretical discoveries, many of which would otherwise be almost indeducible. Likewise, the development of new forms of observation and the installation of finer spatial and temporal observation networks have helped to have greater understanding and better predictions.[124]​.

Research programs, including study projects such as the VOTEX project), the deployment of TOTO, the Doppler On Wheels (DOW) and dozens of other programs, hope to answer many of the questions that still plague meteorologists. highlighting in this sense the National Science Foundation.[101][125]​.

• - Cyclone.

• - Natural disaster.

• - Extreme weather.

• - Whirlwind (meteorology) "Whirlwind (meteorology)").

• - Córdoba Tornado.

• - Delimited weak echo region.

• - Radius of maximum winds.

• - Wikimedia Commons hosts a multimedia category on Tornado.

• - Wiktionary has definitions and other information about tornado.

• - Database of severe weather events in Europe.

• - NOAA storm database 1950-present.

• - NOAA Tornado Preventive Guide.