What’s causing extreme cold in US Midwest

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Mains Paper 1: Geography | Salient features of World’s Physical Geography

From UPSC perspective, the following things are important:

Prelims level: Polar Vortex

Mains level: Polar Vortex


News

  • A record-breaking cold wave has swept through the US Midwest, with 22 states hitting sub-zero temperatures.
  • The extreme cold has been caused by a blast of Arctic air, which in turn is a result of what is known as a “polar vortex” event.

Polar Vortex

  1. It is described as a whirling cone of low pressure over the poles that is strongest in the winter months due to the increased temperature contrast between the polar regions and the mid-latitudes, such as the US and Europe.
  2. The counter-clockwise flow of air helps keep the colder air near the poles.
  3. It spins in the stratosphere, a layer of the atmosphere 10-48 km above the ground and above the troposphere, where most familiar weather patterns develop.
  4. Usually, when the vortex is strongest, cold air is less-likely to plunge deep into North America or Europe.
  5. In other words, it forms a wall that protects the mid-latitudes from cold Arctic air.

When does the polar vortex cause extreme cold?

  1. In winter, the polar vortex sometimes becomes less stable and expands.
  2. Many times during winter in the northern hemisphere, the vortex expands, sending cold air southward with the jet stream.
  3. This is called as the “breaking off” of a part of the vortex.
  4. Normally, when the vortex is strong and healthy, it helps keep a current of air known as the jet stream traveling around the globe in a pretty circular path.
  5. This current keeps the cold air up north and the warm air down south.
  6. But without that strong low-pressure system, the jet stream doesn’t have much to keep it in line. It becomes wavy and rambling.

Is all cold weather the result of a polar vortex event?

  1. Though the polar vortex is always hanging out up North, it takes pretty “unusual conditions” for it to “weaken” for it to migrate far south.
  2. Portions of Europe and Asia also experience cold surges connected to the polar vortex.
  3. By itself, the only danger to humans is the magnitude of how cold temperatures will get when the polar vortex expands, sending Arctic air southward into areas that are not typically that cold.
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