Sudden Stratospheric Warming (SSW) Event: Causes and Effects

Category: Geography and Climate Science

UPSC Notes

A Sudden Stratospheric Warming (SSW) event is a rapid increase in temperature in the stratosphere, usually over the polar regions during winter. Major events can involve a substantial rise in polar stratospheric temperatures over a few days.

How does it occur?

  • Atmospheric planetary waves travel upward from the troposphere.

  • These waves interact with the stratospheric circulation and disrupt the polar vortex.

  • The resulting atmospheric dynamics can cause rapid stratospheric warming.

  • During a major Northern Hemisphere SSW, the zonal-mean westerly winds around 60° north and 10 hPa reverse to easterly winds.

Possible effects

  • Weakening, displacement or splitting of the polar vortex.

  • Changes in atmospheric circulation.

  • Increased probability of cold-air outbreaks in some mid-latitude regions.

  • Potential changes in surface weather over subsequent days or weeks.

Key Pointers for UPSC

  • The stratosphere lies above the troposphere.

  • The polar vortex is a large-scale circulation of cold air around the polar region.

  • SSW is not the same as global warming or a heatwave at Earth's surface.

  • Not every SSW event produces severe winter weather in a particular country.

  • Impacts on India are indirect and depend on complex atmospheric circulation patterns.