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How does the jet stream work?

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Quick answer

The jet stream is a fast, narrow current of air high in the atmosphere that blows from west to east. It forms where cold polar air meets warm tropical air, creating a sharp temperature contrast and a strong pressure gradient. Earth's rotation deflects the wind, and it steers weather systems around the globe.

The jet stream is a fast, narrow band of wind in the upper atmosphere that forms where warm and cold air masses meet. It flows from west to east because the temperature difference between the poles and the equator creates a pressure gradient that strong winds follow.

Step by step

  1. The Sun heats the equator more than the poles, creating a large temperature difference between tropical and polar air.
  2. This temperature contrast causes a steep pressure gradient, with higher pressure in warm air and lower pressure in cold air.
  3. Air rushes from high to low pressure, but Earth's rotation deflects it to the right in the Northern Hemisphere and left in the Southern Hemisphere.
  4. The deflection, called the Coriolis effect, turns the wind so it flows west to east, forming a narrow, fast band.
  5. The jet stream meanders in waves that move weather systems and can bring changes in temperature and precipitation to different regions.

Key things to understand

  1. The jet stream exists near the boundary between the troposphere and stratosphere, about 8 to 15 kilometres above the ground.
  2. It forms where the temperature contrast between cold polar air and warm tropical air is strongest, creating a steep pressure gradient.
  3. The Coriolis effect, caused by Earth's rotation, deflects the air sideways, so the wind blows west to east rather than straight from pole to equator.
  4. The jet stream is strongest in winter because the temperature difference between the poles and the tropics is greatest then.
  5. It meanders in wavy patterns called Rossby waves, which steer weather systems and can bring cold snaps or heat waves to different regions.

Labelled diagram

  1. Sun heats equator

    Tropical air becomes warm and rises, creating low pressure at the surface.

  2. Cold polar air

    Polar regions receive less sunlight, so air is cold and dense, forming high pressure.

  3. Pressure gradient

    Air flows from high to low pressure, creating a strong wind aloft.

  4. Coriolis effect

    Earth's rotation deflects the wind, turning it west to east.

  5. Jet stream forms

    A fast, narrow band of wind emerges near the tropopause.

How the jet stream forms

Real-world examples

  • A flight from New York to London takes about an hour less than the return trip because the jet stream pushes eastbound planes.
  • In winter, the jet stream often dips south over the United States, bringing cold Arctic air to states like Texas and Florida.
  • The jet stream can stall over Europe, causing a heat wave like the one in 2003 that led to many deaths.
  • During El Niño years, the jet stream shifts, affecting rainfall patterns in California and other parts of the world.

Common mistake

✗ Myth: The jet stream is a single, straight river of wind that always blows at the same speed.

✓ Fact: The jet stream is actually a meandering, wavy band that shifts position and strength with the seasons. It can split into two branches or merge, and its speed varies from about 100 to over 300 kilometres per hour.

People also ask

What causes the jet stream to move?
The jet stream moves because of temperature differences between the poles and the equator. When these differences change, the jet stream shifts north or south. It also meanders due to Rossby waves, which are large undulations caused by Earth's rotation and temperature contrasts.
Why does the jet stream flow west to east?
The jet stream flows west to east because of the Coriolis effect. As air moves from high to low pressure, Earth's rotation deflects it to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection turns the wind eastward, creating the characteristic west-to-east flow.
How does the jet stream affect weather?
The jet stream steers weather systems such as storms and fronts. When it is strong and straight, weather moves quickly. When it becomes wavy and slow, weather systems can stall, leading to prolonged rain, heat, or cold in one area. It also influences where storms form and how they track.
Why does the jet stream sometimes cause extreme weather?
When the jet stream becomes very wavy, it can stall and block weather systems from moving. This can lead to prolonged heat waves, cold spells, or heavy rain in one area while another stays dry.
How does the jet stream affect airplane flights?
Aircraft flying eastward with the jet stream get a tailwind and travel faster, saving fuel and time. Flying westward against it slows the plane and increases fuel consumption, so routes may be adjusted.
Is the jet stream the same as the polar vortex?
No, they are different. The polar vortex is a large area of low pressure and cold air over the poles, while the jet stream is a fast-moving river of wind in the upper atmosphere that often sits near the edge of the polar vortex.
Does climate change affect the jet stream?
Scientists are studying this. A warmer Arctic can reduce the temperature difference that drives the jet stream, potentially making it wavier and slower, which may lead to more persistent weather patterns.

Part of the guide: Water & Weather Phenomena →