Sudden Stratospheric Warming (SSW) Event

Source:  NW

Context: Meteorologists have warned that another Sudden Stratospheric Warming (SSW) event may occur in December 2025, potentially disrupting the polar vortex and sending unusually cold Arctic air into parts of the United States.

About Sudden Stratospheric Warming (SSW) Event:

• What is SSW?
  • Sudden Stratospheric Warming is a rapid temperature rise (up to 50°C) in the stratosphere, about 10–50 km above Earth’s surface.
  • It disrupts the polar vortex, the circulation of strong westerly winds around the Arctic, often causing major weather anomalies at the surface.
• How Does SSW Occur?
  • Polar Vortex Formation: In winter, strong westerly winds tighten around the Arctic forming the stratospheric polar vortex, a cold, circular wind belt that traps frigid air high above the pole.
  • Upward Rossby Waves: Large atmospheric disturbances called Rossby waves rise from the troposphere into the stratosphere, carrying energy that disrupts the vortex’s stable circulation.
  • Wave Breaking: When these waves “break,” much like ocean waves, they weaken or even reverse the vortex’s westerly winds, destabilising the entire polar wind system.
  • Rapid Descending Air: As the weakened system collapses, cold stratospheric air descends rapidly, compresses, and warms sharply—creating the sudden stratospheric temperature spike.
  • Vortex Split or Shift: The disrupted vortex can split or drift south, releasing Arctic air into mid-latitudes and triggering cold outbreaks across North America, Europe, or Asia.
• Key Features of an SSW:
  • Rapid stratospheric warming: Up to a 50°C increase within days.
  • Vortex weakening or reversal: Westerly winds turn easterly.
  • Jet stream disruption: The jet stream becomes wavier or blocked.
  • Surface impacts lag: Weather effects appear 1–3 weeks later.
  • Irregular occurrence: Not every winter sees an SSW, and not all events affect surface weather.
• Implications of SSW Events:
  • Weather Impacts:
    • Can cause sudden cold waves, snowstorms, and extended freezing conditions across North America and Europe.
    • May shift storm tracks and create high-pressure blocks over the North Atlantic.
  • Forecast Challenges:
    • Hard to predict more than 7–10 days in advance.
    • Models struggle to pinpoint where the displaced Arctic air will descend.
    • Surface weather may influence the stratosphere, creating complex feedback loops.