Sudden Stratospheric Warming (SSW)
Why in news?
A Sudden Stratospheric Warming (SSW) event is developing in December 2025, potentially disrupting the polar vortex and leading to colder-than-average temperatures in parts of the US and other mid-latitude regions.​
Potential Impacts
- Cold Arctic air could spill southward, triggering extreme winter conditions like heavy snow and below-normal temperatures across North America, Europe, and possibly Asia.
- The polar vortex normally confines cold air to polar regions, but SSW events unlock it, amplifying jet stream disruptions and storm tracks.
- This December event follows a March 2025 SSW that ended the prior Northern Hemisphere winter vortex.​
About Sudden Stratospheric Warming (SSW) event
- Sudden stratospheric warming (SSW) involves rapid temperature rises in the polar stratosphere, often by 50°C or more over days.
- These events disrupt the polar vortex through Rossby wave activity.​
- Rossby waves from the troposphere propagate upward, weakening or reversing the polar vortex's westerly winds.
- This descent of air compresses and heats the stratosphere, mainly in the Northern Hemisphere due to land-induced wave patterns.​
- SSW leads to vortex breakdown, cold air outbreaks at the surface weeks later, and altered jet stream patterns.
- Impacts include increased mid-latitude precipitation, stronger storms, and trace gas mixing affecting ozone.​
Rossby waves
- Rossby waves are large-scale meanders in the atmosphere and oceans caused by Earth's rotation. These planetary waves influence global weather patterns and ocean currents.
- They are form due to the variation in the Coriolis effect with latitude, leading to conservation of potential vorticity in rotating fluids.
- Polar air moves equatorward while tropical air shifts poleward, creating undulations in the jet stream. Heat transfer from equator to poles drives this process.​
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