What is a Jet Stream – Climatology | UPSC, IAS, SSC CGL, CDS, NDA

So what are jet streams?

Jet streams are winds that flow high up in the atmosphere. So these are the layers of atmosphere from highest to lowest :–

  1. Exosphere: 700 to 10,000 km
  2. Thermosphere: 80 to 700 km
  3. Mesosphere: 50 to 80 km
  4. Stratosphere: 12 to 50 km
  5. Troposphere: 0 to 12 km

Jet streams are typically active at 6 – 11 kilometer above the surface of the earth and is mostly found in the troposphere.

Jet streams can flow up to 320 km/h, and they are 1000’s of miles long, 100’s of miles wide, and a few miles thick. Now these strong winds flow in slim strips so that it can break off into smaller winds that can merge with other strips anywhere anytime, that’s how it will have the capability to push air masses around and affect weather patterns. You know… it literally pushes the weather pattern of any particular region. It has that much capability. So the seasons of the year, then location of low and high pressure systems and then air temperature, all of these get effected due to when and where a jet stream travels.

How are jet streams caused?

Jet streams are caused by the temperature difference between tropical air masses and polar air masses. Now we know that tropical air is warm and polar air is cold, and it is due its relative locations. So what happens in one part of the world depends on what is happening elsewhere, after all the atmosphere is one complete environment, it is connected with so many factors.

Now coming to the most intriguing question!

Where the jet stream begins?

It all starts in tropics, that is around the equator. As we know this region is warm because the sun’s rays hit the earth’s surface at a higher angle at the equator. Hence we can also call this place as a place that fuels the jet stream. Now what happens is at the equator the warm air rises up in the atmosphere and goes to this region between troposphere and stratosphere. From here, this warm air gets drawn toward the colder air found in north and south pole. Notice that the warm air molecules are getting attracted towards colder ones. Now at higher altitudes, the warm air cools and sinks drawing more and more warm air behind it. Meanwhile the cooled air flows towards the equator creating a simple looping mechanism. It’s an endless repetition.

Now the next follow up question is,

In which direction does the jet stream flow?

To answer this question we will have to answer another question that is, in which direction does the earth rotate? Now this a very tricky question, people often over-complicate things here. Do not mix you left and right viewpoint with east and west directions. Left and right depends upon your perspective. What is left to you is right to the person standing opposite to you. On the other hand east and west directions are fixed. The sun rises in east regardless of your right and left direction. Therefore the earth rotates from west to east. Due to the earth’s easterly rotation, the warm air at the tropics follows the earth’s momentum and goes in the same direction and makes an angular approach from west toward north and south pole.

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