Jet stream splitting occurs when the polar jet stream divides into two separate branches, disrupting typical weather patterns. This split is usually caused by a combination of atmospheric and climatological factors that change the distribution of temperature and pressure in the upper atmosphere.
Key Causes of Jet Stream Splitting
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Warming in the Arctic: Large reductions in the temperature gradient between the equator and the poles (often due to Arctic amplification and sea ice loss) decrease the jet stream’s strength and make it more prone to splitting.
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Strong Ridging or Blocking Patterns: High-pressure ridges or atmospheric blocks divert the jet stream, sometimes leading it to separate into two pathways—north and south of the block.
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Oscillations and Teleconnections: Phenomena like the North Atlantic Oscillation (NAO), El Niño-Southern Oscillation (ENSO), and the Pacific/North American pattern (PNA) can alter wave patterns in the atmosphere, promoting splits in the jet stream.
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Rossby Wave Amplification: Enhanced meandering of the jet (large north-south swings or "waves") makes it easier for the jet to split when interacting with mountainous regions or other upper-level disturbances.
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Stratospheric Events: Sudden stratospheric warming or cooling events can displace or bifurcate the jet stream temporarily, especially in winter.
Effects on Weather
A split jet stream can create unusual weather patterns, such as prolonged droughts in one region and repeated storms in another, by redirecting storm tracks and altering the delivery of warm or cold air to large areas.
Summary Table
| Cause | Mechanism |
|---|---|
| Arctic warming | Weakens temperature gradient; destabilizes and splits the jet |
| Blocking patterns/ridging | Diverts and separates jet flow |
| Teleconnections (ENSO, NAO) | Modifies wave patterns; encourages split |
| Rossby wave amplification | Large swings cause jet to divide when encountering topography/disturbances |
| Stratospheric disturbances | Sudden warming/cooling events bifurcate jet temporarily |
Jet stream splitting is ultimately a result of dynamic interactions between changing climate conditions, atmospheric waves, and the underlying surface features—leading to highly variable and sometimes extreme weather patterns.
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