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Climate part 2

 

Coriolis force:-               

An apparent force caused by the Earth’s rotation. The Coriolis force is responsible for deflecting winds towards the right in northern hemisphere and towards the left in the northern hemisphere.

The Coriolis force occurs from west to east. This force is very small and can only be noticed when large scale displacement or displacement of large body occurs. Example, displacement of clouds, water in oceans, large air masses etc. This force is zero at equator and maximum at poles.

 

Jet streams:-

Jet streams are fast flowing, narrow, meandering air currents in the atmosphere of some planets including Earth. These are strong winds in upper part of the atmosphere.

1) These bands of winds are thousands of miles long and hundreds of miles wide.

 

2)  Their speed can be up to 250 km/hr.

 

 

3)  These are strong and fast blowing winds so they are accommodating to the aircraft. If the aircraft is travelling in the direction of jet stream, it can travel longer distance is low cost and less fuel.

4)  These winds majorly help in shaping the weather pattern across the globe.

 

Formation:-

Due to pressure difference in atmosphere, three types of cells are formed namely Polar cell, Ferrel cell and Hadley cell. The Jet streams occur in the tropopause (junction between troposphere and stratosphere) and at the junction of two cells. Major factors in the formation of jet streams –

                       Pressure Gradient

                    Temperature difference




 

Let’s now understand jet stream formation pictorially. The Jet stream between polar cell and Ferrel cell is called polar jet stream and the Jet stream between Ferrel cell and Hadley cell is called sub tropical jet streams.

If we talk of polar jet stream, here the wind diverges (observe black arrows) as a result of which there is a pressure difference and a void is created in this region which traps static wind. Hence polar jet stream is formed.

In the case of sub tropical jet stream, the winds converge (observe black arrows). Since the winds are travelling in opposite direction, there a temperature difference between them and they could not merge. Again a void is created where the static wind traps. Hence sub tropical jet stream is formed.

Fun fact: - The major Jet streams are circumpolar i.e. the move around the whole globe in a circular motion. This circular motion is from west to east mainly. Not all jet streams move in this direction. The small ones find their own way.



How do they move:-

The jet streams move in a snake like wavy movement which is called meandering. At some point the meandering reaches the extreme and the air masses start detaching which causes cyclones.

 



Observe the lower part of the jet stream in the picture. When this meandering touches the extreme, the lower part will detach and start spinning causing cyclone.

 

Local jet streams:-

There are two local jet streams:-

ü Tropical jet stream

ü Somali jet stream

When the subtropical jet stream reaches near Tibet, it starts rotating with great velocity due to low pressure condition there and reaches the Arabian Sea. The Somali jet stream comes from Somalia. Both these jet streams help in strengthening the Indian monsoon.  

 

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Location: Amritsar, Punjab, India

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