Why do tornadoes form?

A tornado is a rare local, small-scale, sudden strong convective weather. It is a strong, small-scale strong convective weather caused by air convection movement under strong unstable weather conditions. air vortex. ?

The structure of a tornado includes the funnel cloud as the main part and the convective system that maintains its existence, usually the cumulonimbus clouds brought by thunderstorms.

Funnel Cloud: A violently rotating funnel-shaped cloud tower extending from a cumulonimbus cloud. Sometimes it stretches out and disappears, sometimes it hangs in the air or touches the ground. The axis of a tornado funnel cloud is generally perpendicular to the ground. In the later stages of development, when the wind speed difference between the upper and lower layers is large, it can become tilted or curved. The smallest diameter of its lower part is only a few meters, usually hundreds of meters, and the largest can reach more than a thousand meters. The diameter of the upper part is generally several thousand meters, and the largest can reach 10 kilometers. The central air pressure in the funnel cloud is very low, resulting in large horizontal pressure gradients and wind speeds. Funnel clouds may not directly reach the underlying surface, but if they are close to the ground, they may lift up water, dust, and sediment.

Cumulonimbus clouds that produce tornadoes are called parent clouds. The parent cloud determines the speed and direction of the tornado. The moving speed of parent clouds is usually 40 to 50 kilometers per hour, and the fastest can reach 90 to 100 kilometers. The moving path is mostly linear, usually several kilometers, and some can reach dozens of kilometers. The appearance of parent clouds is related to frontal cyclones, tropical cyclones after landfall, thunderstorms, etc. The parent cloud of a tornado is usually a convective cloud system, such as part of a thunderstorm towering cumulus cloud, which appears as a continuously rotating cloud wall.

Meteorological parameters

The diameter of a tornado ranges from a few meters to several hundred meters, with an average of about 250 meters and a maximum of about 1,000 meters. The diameter in the air can be several kilometers, with a maximum diameter of 10 kilometers. The maximum wind speed in the center can reach 100 to 200 meters per second, and the duration of a tornado is generally only a few minutes, but the longest is only a few hours. Everything was robbed wherever he went. The funnel-shaped center of the tornado consists of sucked dust and condensed water vapor forming a visible "dragon's mouth". Over the ocean, especially in the tropics, similar phenomena occur called maritime tornadoes.

Tornadoes are usually extremely fast. It is not surprising that the wind speed is 100 meters per second, and even reaches more than 175 meters per second, which is five or six times greater than a Category 12 typhoon. The scope of the wind is very small, generally only 25 to 100 meters in diameter, and only in rare cases the diameter reaches more than one kilometer; it only takes a few minutes, or at most a few hours, from occurrence to disappearance. Most tornadoes spin counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, but there are exceptions.

Tornado generation

Tornado is a form of concentrated release of unstable energy near the ground in a small area. There are no clear conclusions on the atmospheric microphysics of tornadoogenesis? But in terms of dynamics, it is considered to be related to updrafts and vertical wind shear, and can be roughly divided into four stages?:

The convective system brings unstable energy in the atmosphere and triggers updrafts.

The rising airflow generates vertical vorticity under the action of wind speed and wind shear, that is, it begins to rotate in the horizontal direction.

The rotating system develops into the interior of the convective system under the action of convergent airflow, forming a tornado core in the middle troposphere.

Under the action of the downdraft in the front of the convective system, the vortex developed in the core of the tornado extends to the downward surface, the surface air pressure drops sharply, and the surface wind speed rises sharply, forming a tornado.

Classification of tornadoes

Multiple vortex tornadoes

Multiple vortex tornadoes refer to tornadoes with two or more vortices rotating around the same center. The development of multi-vortex structures is related to the intensity of the tornado, and these small vortices tend to cause greater damage in the area where the main tornado passes. ?

Waterspouts

A waterspout or seaspout can simply be defined as a tornado over water, usually meaning a non-supercell tornado over water. Waterspouts can occur in oceans and lakes around the world. In the United States, waterspouts commonly occur along the southeastern coast of the United States, especially in southern Florida and the Gulf of Mexico. Although waterspouts are by definition a type of tornado, they are less destructive than the most powerful prairie tornadoes, but they are still quite dangerous. Waterspouts can overturn small boats and destroy ships. When they hit land, they can cause even greater damage and take lives. The National Weather Service will often issue special marine warnings when waterspouts are likely or visible over coastal waters, or tornado warnings when waterspouts are moving toward land. ?

Landspout

Landspout (called dust-tube tornado by the National Weather Service) is used to describe a type of tornado that is not related to mesoscale cyclones. Landspouts and waterspouts share some characteristics, such as relatively weak intensity, short duration, small funnel clouds formed by condensation, and often not touching the ground. Although relatively weak, landspouts can still bring strong winds and severe damage. ?

Other similar weather phenomena

A fire tornado has a shape similar to a tornado, consisting of a combination of whirlwind and flames?

In 2010, Brazil, located in the southern hemisphere, encountered rare drought and drier weather, and wildfires broke out in many parts of the country. On August 24, a tornado blew up from a fire spot in Sao Paulo, Brazil, forming a rare fire tornado landscape. The tornado picked up flames several meters high, spinning forward like a huge fire dragon. This "fire dragon wind" was photographed on the 24th. The "fire dragon" flew several meters high over the burning fields, blocking a highway. In order to extinguish this "fire dragon", the local area dispatched helicopters. The area where the "Fire Dragon Wind" appeared has not had rain for three months. Unusually dry weather and strong winds have fueled the fires here. Brazil's Global TV reported that the air in Sao Paulo has become as dry as the Sahara Desert.