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Meteorologists have recently warned of a potential Sudden Stratospheric Warming (SSW) event, which may cause below-average temperatures across parts of the United States and other mid-latitude regions later this month.

What is Sudden Stratospheric Warming?

• Sudden Stratospheric Warming (SSW) is a phenomenon marked by a rapid increase in stratospheric temperatures, sometimes by 30–50°C within a few days.
• It results in the weakening, displacement, or splitting of the polar vortex, a cold air system usually confined to the polar regions.

Mechanism of SSW

• SSW events are triggered by large-scale atmospheric (Rossby) waves generated in the troposphere.
• These waves propagate upward into the stratosphere and break over the polar vortex, similar to ocean waves.
• If sufficiently strong:
  • The westerly winds of the polar vortex weaken or reverse to easterlies
  • The vortex loses its circular symmetry
• This causes descending air to warm adiabatically, leading to sudden temperature rise in the stratosphere.

Impact of SSW

• The weakened or split polar vortex allows cold Arctic air to spill southward into the mid-latitudes.
• This can result in:
  • Cold waves
  • Severe winter weather
  • Below-normal temperatures over regions such as:
    • North America
    • Europe
    • Asia

Polar Vortex: Key Features

• A large, persistent low-pressure system containing cold air around both poles.
• Extends from:
  • Tropopause
  • Through the stratosphere
  • Up to the mesosphere (above ~50 km)
• Seasonal behavior:
  • Stronger in winter
  • Weaker in summer
• During winter, it can expand and interact with the jet stream, pushing cold air southward.

Role of Jet Streams

• Jet streams are narrow bands of strong winds located in the upper troposphere (~9–12 km altitude).
• They act as a conduit for polar air outbreaks during polar vortex disturbances.
• Such interactions are common during Northern Hemisphere winters.