Jet Streams : Types, Characteristics, Significance | UPSC Notes

What are Jet Streams?

Jet streams are fast-flowing narrow-band currents of air formed in the upper atmospheres of some planets (including Earth), mostly from west to east. The average speed of the Jet Streams is 110 miles. However, the extreme temperature difference between cold and warm air can lead to its high speed, which can be as high as 250 mph (or even faster).

• Wind speed is not directly north and south but is influenced by wind speed as you move away from the equator. This is due to speed and how fast the space on or above the Earth moves relative to the Earth’s axis.
• Wind speed is conserved as it travels around the Earth. This implies that as the air above the equator begins to move toward one of the poles, it keeps its eastward speed constant. However, the Earth beneath the air moves slower as the wind moves toward the poles.
• Lastly, Jet Streams have an immense influence on weather conditions, and they have a close relationship with temperate cyclones and the Indian Monsoon. Therefore, it is crucial to understand the concept of jet streams to learn about the Indian climate.

Genesis of Jet Streams

The genesis of the Jet-Streams is provided by three kinds of gradients:

• The pressure gradient between the pole and equator
• The pressure gradient between surface and subsurface air over the poles.
• The thermal gradient between the pole and the equator.

Factors Influencing Jet Streams

The Coriolis effect and landmasses are two factors that influence the flow of Jet Streams. The flow of the jet is disrupted by landmasses due to friction and temperature differences, and the meandering movement of the Jet Streams is due to the earth’s spinning nature. As the meandering sections of the stream interact with landmasses, they create a state of flux. This results in temperature differences.

The strength and position of the stream can also be affected by the temperature of the stratosphere in the winter. The stronger the jet stream, the cooler the polar stratosphere. The strength and amplitude of the Jet Streams can also be affected by the warmth of the landmasses and oceans.

Types of Jet Streams

The Jet Streams are of the following types:

Polar Front Jet Streams

• They are present in the convergence zone of the surface polar cold air mass and tropical warm air mass (sub-polar low-pressure belt), somewhere between 40 degrees and 60 degrees latitude.
• Polar Front Jet Streams have a more variable position than the subtropical jets and move in an easterly direction.

Polar Night Jet Streams

• They develop in the winter season due to the steep temperature gradients in the stratosphere around the poles.
• During the winter months, when the nights are much longer, the air high above the poles becomes much colder than the air over the Equator.
• The polar night jets, which move eastwards at an altitude of about 48 kilometers, are created by extreme air pressure differences in the stratosphere. These, when combined with the Coriolis effect, produce extreme air pressure differences in the stratosphere.
• During the summer, the polar night jet travels at a higher altitude of about 24,000 meters.

Subtropical Westerly Jet Streams

• They are best developed in winter and early spring, and their maximum speed approaches 300 knots, which is associated with the merger with polar-front jets.
• They move from west to east.
• They move north of the subtropical high-pressure belt in the upper troposphere in both hemispheres, above 30 degrees to 35 degrees latitude.
• Also known as stratospheric subpolar Jet Streams. They are produced by the earth’s rotation and flow for the majority of the year.
• Their circulation is more regular than the polar front jet stream.

Tropical Easterly Jet Streams

• They are upper-level easterly winds that originate in late June and last until early September.
• The jet’s strongest development occurs about 15 kilometers above the Earth’s surface, over the Indian Ocean, with wind speeds of up to 40 meters per second.
• They occur near the tropopause in Southeast Asia, India, and Africa during summer.
• The difference in heating and cooling of winds, along with the pressure gradient is the reason behind this jet.

Local Jet Streams

• They are formed locally as a result of local thermal and dynamic conditions.
• They have limited local importance.

Characteristics of Jet Streams

Jet Streams are high-velocity winds (400-500km/hr). This high velocity is due to great thermal contrast creating a powerful pressure gradient force. The effect of Earth’s rotation causes Jet Streams to circulate from west to east. The other characteristics include:

• They are circumpolar, i.e., they move around the poles in both hemispheres.
• Their circulation path is wavy and curving.
• The flow of the Jet Streams is 3-dimensional, and it develops crests and troughs.
• They have seasonal variations and shift with the apparent movement of the sun.

How Jet Streams Affect the Indian Climate

The Indian climate is predominantly influenced and dominated by Sub Tropical Jet Streams (STJ). The northward movement of the subtropical jet is the first indication of the onset of the monsoon over India. The monsoon’s onset and withdrawal are often predicted by the Jet Stream’s periodic movement.

• The onset of the monsoon season in India is signaled by the subtropical stream moving northward.
• During the summertime, there is increased solar heating of the Indian subcontinent, which results in a tendency to form a cyclonic monsoon cell situated between the Indian Ocean and southern Asia.
• The STJ deflects northwards and crosses over the Himalayan Range. The altitude of the high mountains initially disrupts the jet, but once the STJ crosses the high summits, it is able to reform again over central Asia.
• Warmth and moisture are fed into the cell by a lower-level tropical jet stream which brings with it air masses laden with moisture from the Indian ocean. As these air masses are forced upward by north India’s mountainous terrain, the air is cooled and compressed, it easily reaches its saturation vapor point, and the excess moisture is dissipated in the form of monsoon rains.
• The easterly winds become very active in the upper troposphere and they are associated with westerly winds in the lower troposphere. This results in a more active southwest monsoon and heavy rainfall are caused.
• The end of the monsoon season is brought about when the atmosphere over the Tibetan Plateau begins to cool, this enables the STJ to transition back across the Himalayas.
• The winter subtropical westerly Jet Stream blows from the west to the east in the entire west and middle of Asia and is divided by the Himalayan ranges and Tibetan Plateau.
• One of the branches blows parallel to the plateau from the north while the other moves towards the east in the south of the Himalayas.

South Asia’s monsoon is largely influenced and controlled by Jet Streams. In India, the southwest monsoon is linked to the tropical easterly stream, which can be found between 8 and 35 degrees north latitude. The subtropical westerly Jet Stream, which blows between 20 and 35 degrees latitude in both hemispheres during the winter, is linked to the northeast monsoon.

Significance of Jet Streams

Jet Streams have a significant impact on local and regional weather patterns, and when they collide with surface wind systems, they result in severe storms.

• Temperate cyclones and Jet Streams have a close relationship in terms of intensity.
• The Jet Streams help in providing a relatively clear picture of the occurrence of El Nino and La Nina events.
• Pilots take the help of the Jet Streams when they have to fly in the direction of the jet stream’s flow. It makes the movement smooth.

Jet Streams UPSC

Jet Streams is a part of the Geography section of the UPSC Syllabus. It is a crucial topic from both UPSC Prelims and UPSC Mains exam points of view. As geography is a part of both the UPSC Prelims Syllabus and the UPSC Mains Syllabus, candidates need to make sure they cover every possible section of the topic. To cover the topic of Jet Streams in a better manner, candidates can take the help of NCERT Books for UPSC to understand the basic concepts. Following this, UPSC Books for Geography can be consulted.

Jet Streams UPSC Questions

Question: With reference to the Easterly Jet stream, consider the following statements:

1. An Easterly Jet Stream flows over the southern part of the peninsula and steers the tropical depressions into India.
2. In August, it is confined to a 15-degree latitude and shifts northward thereafter and crosses the Himalayas.

Select the correct answer using the code given below.

1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2

Answer: Option A

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