Tornadoes are caused by a combination of specific atmospheric conditions, primarily instability and wind shear, that create rotating thunderstorms called supercells.
Key Ingredients for Tornado Formation
The development of a tornado requires a specific set of atmospheric circumstances to come together:
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Instability: This refers to warm, moist air near the ground and cooler, dry air aloft. This unstable environment allows air to rise rapidly, fueling thunderstorms.
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Wind Shear: This is a change in wind speed and/or direction with height. Wind shear creates a horizontal spinning effect in the lower atmosphere.
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Supercell Thunderstorms: When the horizontal spinning from wind shear is tilted vertically by strong updrafts within the thunderstorm, it forms a rotating column of air called a mesocyclone.
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Mesocyclone Formation: The updraft within a supercell thunderstorm can tilt the horizontal vortex tubes (created by wind shear) into the vertical, forming a rotating column called a mesocyclone.
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Tornado Development: Not all mesocyclones produce tornadoes. When the mesocyclone strengthens and descends, a visible funnel cloud may form. This funnel cloud becomes a tornado when it touches the ground.
Detailed Explanation
| Factor | Description |
|---|---|
| Instability | Warm, moist air near the surface rising into cooler, drier air aloft creates an unstable environment ripe for thunderstorm development. |
| Wind Shear | Changes in wind speed and direction with height create a horizontal "rolling" effect in the atmosphere, which is crucial for rotation. |
| Supercells | The strongest thunderstorms that contain a rotating updraft (mesocyclone). These are the most likely storms to produce tornadoes. |
The Process
- Unstable Air Mass: Warm, moist air rises rapidly.
- Wind Shear Creates Rotation: Wind shear creates a horizontal rolling effect.
- Supercell Development: The rotating air is tilted vertically by the updraft, forming a mesocyclone.
- Tornado Formation: If conditions are right, the mesocyclone intensifies and stretches downward, forming a tornado.
Not All Supercells Produce Tornadoes
It's important to remember that only a small percentage of supercell thunderstorms actually produce tornadoes. The exact mechanisms that determine why some mesocyclones produce tornadoes and others do not are still being researched.
