What is a tornado?
Tornadoes are rapidly rotating columns of air that are simultaneously in contact with the surface of the Earth and a cumulonimbus cloud. These funnel clouds are visible to the human eye and often carry with them a surrounding cloud of debris and dust.
With intense destructive power from wind speeds that can exceed 300 miles per hour, tornadoes can wreck havoc on buildings, throw cars, and toss large debris through the air.
The severity of a tornado is measured with the Enhanced Fujita Scale (EF Scale) that ranges from EFO (weakest) to EF5 (strongest).
How do tornadoes form step by step?
Tornadoes form from severe thunderstorms, typically known as supercells, which have a rotating updraft called a mesocyclone.
Here’s the basic process:
- Atmospheric Conditions: A combination of warm, moist air near the surface and cooler, drier air above. This setup creates instability in the atmosphere.
- Wind Shear: Horizontal wind shear (change in wind speed and direction with height) is also crucial. When warm air at the surface begins to rise, it can tilt the rotating air from horizontal to vertical due to the wind shear.
- Supercell Development: This vertical column of rotating air can become part of a larger storm system or supercell. Supercells are characterized by a persistent, rotating updraft called a mesocyclone.
- Tornado Genesis: Under the right conditions, part of the mesocyclone can tighten and intensify, eventually extending towards the ground as a tornado.
- Tornado Lifecycle: Tornadoes can last from a few minutes to over an hour before dissipating. The length of a tornado’s lifecycle can vary greatly depending on atmospheric conditions.
The exact combination of factors and the process can vary, and not all supercells produce tornadoes. However, the presence of a mesocyclone in a supercell is a key indicator that tornado formation is possible.
How and why do tornadoes stop?
Tornadoes stop primarily due to changes in the atmospheric conditions that sustain them. These are the key factors that lead to the end of a tornado’s destruction:
- Loss of Instability: Tornadoes are fueled by unstable atmospheric conditions, where warm, moist air meets cooler, drier air. When this instability decreases, the energy available to sustain the tornado diminishes.
- Parent Thunderstorm Weakens: Tornadoes are typically spawned from supercell thunderstorms. If the parent thunderstorm weakens or changes structure, the tornado may lose its primary source of energy and circulation.
- Interaction with Terrain: When a tornado moves over rough terrain, such as hills, forests, or urban areas, the friction and disruption can weaken its rotation. This can lead to the tornado dissipating.
- Inflow Interruption: Tornadoes rely on a steady inflow of warm, moist air. If this inflow is interrupted or redirected, the tornado can weaken. This can happen if the storm moves into an area with different atmospheric conditions or if the inflow is disrupted by other weather phenomena.
- Occlusion Process: In some cases, the tornado may undergo an occlusion process, where the rear flank downdraft (a downdraft on the backside of the storm) wraps around the tornado, cutting off its warm air supply and causing it to weaken and dissipate.
Where do tornadoes occur around the world?
Tornadoes occur all around the globe, but some areas experience them much more than others.
| Country/Continent | Region |
|---|---|
| United States | The central part of the United States, known as “Tornado Alley,” experiences the most tornadoes in the world. This area includes parts of Texas, Oklahoma, Kansas, Nebraska, and South Dakota. |
| Canada | While not as frequent as in the United States, Canada, particularly in the Prairie provinces (Alberta, Saskatchewan, and Manitoba) and Southern Ontario, experiences a significant number of tornadoes each year. |
| Bangladesh and Eastern India | Bangladesh and eastern India see frequent tornado activity, especially during the pre-monsoon season. |
| Argentina and Uruguay | The Pampas region in Argentina and parts of Uruguay experience tornadoes, particularly during spring and summer. |
| Australia | Tornadoes occur in Australia, particularly in the southeastern and western parts of the country. They are most common during the summer months when conditions for severe thunderstorms are favorable. |
| Europe | Tornadoes are less frequent in Europe but can still occur, particularly in countries like the United Kingdom, Germany, and Italy. These tornadoes are generally less intense than those in Tornado Alley. |
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