Climatology

Jet streams and how they affect the climate?

Introduction

In this article, I will discuss the jet streams, types of Jet stream and their characteristics. These topics are very important for the students of geography. Also, Jet Stream is a hot topic for many entrance exams like UPSC, BPSC and other state exams. After reading this article, you will easily distinguish between the various types of jet streams formed in the atmosphere due to various factors.

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Jet streams

Jet Streams are the fast-flowing winds. They are narrow and meandering air currents in the atmosphere. They flow in narrow cores due to the strong pressure gradient. The speed of the wind is high at the center of the jet stream. The velocity of wind decreases away from the center. They occur near the Troposphere.

Video source- Jetstreams

Effect of Jet Stream

  1. Due to the strong current of rapidly moving air, it can push weather patterns around the world.
  2. Also, the position and strength of these streams help meteorologists to forecast future weather events.
  3. The world’s jet streams are also impacted by ELNINO and LA NINA.
  4. The precipitation usually increases in California, because of polar jets.
  5. When these streams are positioned above temperate cyclones, they yield more precipitation than normal.

Wind profile of Jet Stream

Formation of jet streams

What are the characteristics of jet Stream?

  1. The length profile of a jet stream varies between 1600km to 3200km.
  2. They follow the curved and meandering path due to the Coriolis effect.
  3. These streams cover hundreds of kilometres in width and a few kilometres in depth.
  4. The height of the jet stream decreases from the equator towards the pole since the height of the troposphere decreases from the towards the poles.
  5. They do not flow a straight path.
  6. These atmospheric circulations mainly flow a wavy path in the form of Rossby waves.
  7. They are characterized by vertical and lateral wind shear.
  8. They are characterized by great seasonal variations.
  9. During the colder part of the year, they extend towards the equator.
  10. In summers, they narrow down.
when were the jet streams discovered?

Meteorologist came to know about the existence of jet streams during the 2nd World War when the American jet was obstructed by the flow of these meandering waves during the bombing mission over Japan.

why do they move faster during the winters?

These winds have high velocity during the winters because of the steep horizontal temperature gradient.

How Jet streams are formed?

The origin of these atmospheric circulations is associated with the temperature gradient between pole and equator. This gradient induces a westerly component to flow aloft.

Where they normally located?

The Jet stream is found in the upper-level westerlies, where the temperature gradient or pressure gradient becomes stronger. This happens in the vicinity of the polar front and subtropics.

What is the significance of jet streams?
  1. There is a close relationship between the intensity of mid-latitude cyclones and jet streams.
  2. Due to these fast-moving winds, the cyclones become stronger and stormier.
  3. When the jet streams are positioned above temperate cyclones, they yield more precipitation than normal.
  4. Jet streams sometimes break through the tropopause and enter into the Lower Stratosphere.
  5. The stratosphere develops cirrus clouds by injecting some of the water vapour by the jet streams.
  6. The monsoon of South Asia is largely affected and controlled by jet streams.

Types of Jet stream?

Jet streams are broadly divided into four types. They are classified based on their location and metrological properties.

  1. Polar front jet stream
  2. Subtropical jet stream
  3. The tropical easterly jet stream
  4. Polar night jet stream
  5. Somali jet stream or cross-equatorial jet stream

Polar front jet stream

  1. The polar jet stream was discovered by Rossby and this jet stream is also known as the primary jet stream.
  2. Polar front jet streams are formed above the convergence zone (40⁰-60⁰ latitude) of the surface polar cold air mass and the tropical warm air mass. Here the thermal gradient is steep due to two contrasting air masses.
  3. Polar jet streams move from west to east direction.
  4. They follow an irregular path.
  5. They may encircle the entire globe.

Subtropical westerly jet stream

  1. Subtropical jet streams are found in the upper troposphere just to the north of subtropical high-pressure belt i.e. above 30⁰-35⁰ latitudes.
  2. They originate at the meeting point of Hadley and Ferrel cell.
  3. The subtropical jet stream exists due to the increase in velocity. This velocity is induced by the conservation of angular momentum.
  4. They occur as an air parcel and move towards the poles from the equator.
  5. Subtropical jet streams are found at a higher altitude as compared to polar front jet streams.
  6. They move from west to east direction in a more regular manner.
What is the significance of Subtropical jet stream?
  1. Subtropical jet streams help in steering the temperate cyclones towards India in Winter.
  2. They cause winter rainfall in India due to western disturbances.
  3. Subtropical jets decide the day of the monsoon burst date.

Tropical easterly jet stream

  1. Tropical easterly jet stream develops in the middle troposphere.
  2. They are found above the surface easterly trade winds over India and Africa in the Northern hemisphere.
  3. They are located at an altitude of 10km-12km above the Gangetic plains.
  4. The tropical easterly jets formed due to summer-time heating of Tibetan Plateau.
  5. The heating of the Tibetan plateau leads to the formation of a warm-core anticyclone over this plateau in the middle troposphere.
  6. On the southern side of this upper air anticyclone, the direction of airflow is from east to west.
  7. These easterly winds blowing in the mid-troposphere are known as easterly jet streams.
Jet streams in January
Jet streams in June
What is the significance of tropical easterly jet stream?
  1. The tropical easterly jet stream steer the depression formed in the Bay of Bengal towards the eastern coast of India.
  2. Easterly jet stream facilitates the rain in these regions.
  3. They help in intensifying southwest monsoon by increasing the pressure over the Southern Indian Ocean.

Polar night jet stream

  1. Polar night jet stream develops in the winter season due to a steep temperature gradient in the Stratosphere.
  2. They are found at a height of 30 kilometers.

Somali or cross-equatorial jet stream

  1. Somali jet streams are formed due to the unequal heating of the continent of Africa.
  2. They cross the equator hence it is also known as cross-equatorial jet streams.
What is the significance of Rossby waves?
  1. Rossby waves balance the spatial heat.
  2. They lead to the genesis of temperate cyclones.
  3. Rossby waves can purify atmospheric impurities.
Figure-4. Rossby waves
What are the stages of formation of jet stream?
Stage-1
  • In the first stage, the position of Jet Stream is near the poles.
  • It is separated by polar cold air mass in the north and warm westerlies in the south (in the Northern hemisphere).
  • The jet stream is almost straight from west to east.
Stage-2
  • The warm air pushes polewards and cold air enters the territory of warm air.
  • Thus, the waves are formed called Ross by waves.
Stage-3
  • In this stage, the meandering course of Rossby waves is fully developed.
  • The warm air enters the region of cold air and cold air moves into the southern warm region.
  • This marks the beginning of the death of Jet Stream.
Stage-4
  • In this stage, the cold and warm air fully exchange their territories. The meanders of these streams are cut off.
  • A thin demarcating zone is found between the cold and warm air mass.
  • The heat exchange has taken place, with the dissipation of Ross by waves the jet stream also dissipates.

Rajneesh Kumar Thakur

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