Tornadoes
A tornado is a violently rotating column of air extending from the base of a thunderstorm (usually a Cumulonimbus or large Cumulus) to the ground.
Characteristics
- Formation: Typically associated with severe thunderstorms, especially supercells. They require great instability and strong vertical wind shear (warm, moist air at the surface, cold, dry air aloft).
- Funnel Cloud: This is the initial stage, when the vortex descends from the cloud but does not yet touch the ground. It becomes a tornado upon making contact with the surface.
- Dimensions:
- Average diameter: Around 100 meters.
- Maximum: Can reach 300 meters or more in extreme cases.
- Rotation Speed: Winds around the core can exceed 200 knots.
- Movement Speed: The tornado moves over the ground at a typical speed of 20 to 40 knots.
- Duration: Generally short, less than 10 minutes, although they can last up to 30 minutes.
- Pressure: The core of the tornado is an area of extremely low pressure.
Global Occurrence
- United States ("Tornado Alley"): The region with the highest global incidence (average > 1000 tornadoes/year). This is due to the frequent clash between warm tropical air from the Gulf of Mexico and cold polar air from Canada.
- Europe: Tornadoes do occur (approx. 300/year), but they are generally less frequent, of lower intensity, and smaller diameter (100-150 m) than in the USA.
- Global: Can form almost anywhere on Earth if conditions are suitable.
Related Phenomena
- Dust Devil: A small vortex that forms from the ground upwards due to strong surface heating (thermal). Occurs on hot, dry days, without the need for storm clouds.
- Waterspout: A tornado that occurs over water.