What’s Jet Stream?

January 22, 2026

jet stream is a high speed, narrow band of westerly wind at high altitude !

題外話： 重推本文係因為我study buddy 同我溫書後，我覺得吾太熟呢個topic! 😆

How fast (is the speed) of a jet stream?

Typical jet stream can has a speed of 100 KT to 200 KT!

BUT minimum at least 60KT

Fact check info on https://skybrary.aero/articles/jet-stream#:~:text=A%20second%20jet%20stream%20sometimes,particularly%20over%20south-east%20Asia.

How high of the location of jet stream?

In between 9-16 km, if my memory correct: it is equivalent to approximately FL300 to FL500.

Rightly, it is near the tropopause height.

X-check info: https://www.noaa.gov/jetstream/global/jet-stream

What doesn’t “narrow band” means?

You can imagine the jet stream is a flat tubular (column) of air current – with only few kilometre in thickness!

Let’s talk about how to form / why the jet stream form?

Here’s a step-by-step breakdown:

  1. Uneven Heating: The Sun heats the equator more than the poles, creating large temperature differences.
  2. Coriolis Effect: Earth’s rotation deflects the air (right in the Northern Hemisphere), turning the wind from north-south into a predominantly west-to-east flow, creating the jet stream.
  3. Jet Stream Formation:
    Using the Polar Jet Stream as an example, it is formed as a result of the temperature gradient between the cold polar air mass and the warmer sub-tropical air mass. 

Types of jet stream?

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