Jet Streams- Origins, Climatic Importance, Types, Characteristics

Jet streams are bands of long, narrow, high-speed winds. Jet streams are distinguished by high vertical shearing action generated by wind motions, which is regarded to be substantially responsible for clear air turbulence. Learn all about jet streams in this article.

Jet streams

• Jet streams are large swaths of intense wind that flow from west to east across the globe. They have an impact on the weather, air travel, and many other aspects of the atmosphere. 
• Flows at 20,000 to 50,000 feet height.
• Jet streams form when air of different temperatures and air masses collide. As a result, surface temperatures usually determine where the Jet Stream forms.
• The larger the temperature difference, the greater the speed of the wind within the jet stream.
• Jet streams span from 20 degrees latitude to the poles in both hemispheres.

Origins Of Jet Streams

Jet stream formation is influenced by three types of gradients:

• The thermal gradient between the poles and the equator.
• The difference in pressure between the poles and the equator
• There is a pressure difference between surface and sub-surface air over the poles.

From Where Does The Jet Stream Start?

Warm air in the tropics and near the equator powers the Jet Stream’s ascent. It is forced toward the colder air at the north and south poles when it reaches the tropopause at around 58,000 feet.

Jet Streams Climatic Importance

• Jet streams transfer moisture to the stratosphere, resulting in the production of Noctilucent clouds.
• It is especially important at the beginning and end of the monsoon season.
• It is known to have transported some ozone-depleting compounds into the stratosphere, causing ozone layer depletion.
• When an air mass travels, it encounters alternate expansion and compression, resulting in alternate high and low pressure.

Characteristics

• Its genesis can be traced back to the thermal contrast of air cells like Hadley cells and Ferrel cells.
• The whirling motion of the Jet Stream is referred to as the ‘Rossby Wave.’
• The equatorial extent of the Jet Stream is greater in winter due to the southern shift of the pressure bands.

Types Of Jet Streams

Sub Tropical Jet Streams:

Jet streams are most common in the winter and early spring. Their top speed is 300 knots due to the fusion with polar-front jets. Subtropical jets are accompanied by a subsidence motion, resulting in generally pleasant weather in the areas they travel over. They occasionally travel north and collide with a polar-front jet.

Tropical Easterly Jet Stream 

The jet stream flows close to the tropopause across Southeast Asia, Africa and India in the summer. Over the Indian Ocean, this jet indicates a deep layer of warm air to the north and colder air to the south. The differential in heating and cooling, as well as the associated pressure gradient, accelerate the jet.

Polar-Night Jet Stream

The Jet Stream runs across the upper stratosphere above the poles. They can be found in the convergence zone above the subpolar low-pressure band.

The Mechanism Of The Indian Monsoon And The Role Of Subtropical Jet Streams

• The intensity of monsoons is determined by upper air circulation, which is dominated by Subtropical Jet Streams (STJ).
• The southwest monsoon that arrives in India is associated with a tropical easterly stream. It blows between latitudes of 8 and 35 degrees north.
• The northeast monsoon (winter monsoon) is associated with the subtropical westerly Jet Stream, which blows in both hemispheres between 20 and 35 degrees latitude.

Seasonal Migration Of The Subtropical Jet Stream

• STJ flows along the southern slopes of the Himalayas in the winter and drastically turns northwards in the summer, flowing along the edge of the Himalayas in early June and along the northern edge of the Tibetan Plateau in late summer (July-August).
• The Jet Stream’s periodic movement frequently heralds the commencement and subsequent withdrawal of the monsoon.
• The shift of the subtropical jet northwards is the first sign of the commencement of the monsoon over India.

STJ In Summer

• At the start of summer, the STJ begin their northwards march.
• Northern India’s weather becomes hot, dry, and squally as a result of increased incoming sun radiation and hot winds like a loo.
• The Equatorial Trough flows northwards across India as the STJ weakens south of Tibet, but the monsoon does not begin until the upper-air circulation has changed to its summer pattern.
• The southern jet had broken up and diverted to the north of the Tibet Plateau by the end of May. There is an unexpected monsoon downpour.
• Hot winds from the Tibetan plateau start the clockwise looping origin in the middle troposphere. It splits as it ascends to the tropopause. The easterly Jet Stream moves towards the equator, while the westerly Jet Stream moves toward the poles.
• The western and eastern jets flow north and south of the Himalayas, respectively. The eastern jet becomes stronger and settles about 15° N latitude.
• In the high troposphere, easterly winds become quite active, interacting with westerly winds in the lower troposphere.
  As a result, the southwest monsoon intensifies, resulting in heavy rain. It is considered to have originated as a result of the very hot plateaus of Tibet and Central Asia.

STJ In Winters

• The subtropical westerly Jet Streams blow from west to east across western and Central Asia during the winter.
• It is divided by the Tibetan Plateau and the Himalayan peaks. One of the streams blows northwards parallel to the plateau, while the other blows eastward in the Himalayas.
• These westerly winds bring the western disturbances that approach the Indian subcontinent throughout the winter.
• Along 25° north latitude, the southern stream sweeps to the south of the Himalayan peaks.

Jet streams have a wide-ranging impact on some parts of the world. Theories that explain and predict the impacts are continually emerging.

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