Warm air masses collide with cold air masses in the atmosphere, forming Jet Streams. To the north and south of the Himalayas, the western and eastern jets streams, respectively, flow. The eastern jet amplifies and arrives at 15 degrees north latitude. This causes the southwest monsoon to become more active, resulting in heavy rainfall. Understanding the Jet Stream is critical for comprehending temperate cyclones and the Indian monsoons. This article will explain to you about Jet Streams which will be helpful in preparing Geography for the UPSC Civil service exam.

What exactly are Jet Streams?

• In the upper atmosphere, jet streams are relatively narrow bands of strong wind.
• Jet streams blow from west to east, but the flow frequently shifts to the north and south.
• This airband can be 160-480 kilometres wide and 900-2150 kilometres thick, with a core speed of over 300 kilometres per hour.
• Aircraft routes that run counter to jet stream's movements are restricted due to their strength.
• Jet streams are associated with major tropopause breaks.

Factors Influencing Jet Streams

• The landmasses and the Coriolis effect are two factors that influence the flow of the jet stream.
• The flow of the jet is disrupted by landmasses due to friction and temperature differences, and the earth's spinning nature emphasises these changes. The meandering movement is the result of this.
• As the meandering sections of the stream interact with landmasses, they create a state of flux and, as a result, temperature differences.
• The strength and position of the stream can 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 stream can be affected by the warmth of the landmasses and oceans (such as the El Nino Southern Oscillation).

Characteristics of Jet streams

• The effect of Earth's rotation causes Jet streams to circulate from west to east.
• In both hemispheres, the circulation is generally observed between the poles and 20 degrees latitude.
• As they move around the poles in both hemispheres, they are also known as circumpolar.
• On the trajectory, their circulation path is wavy and curving.
• Because of the northward shift, the extent narrows during the summer, but during the winter, it can reach up to 20 degrees latitude.
• These can be up to 40 kilometres wide and 2-3 kilometres deep.
• The average wind speed is extremely high, with a winter low of around 120 km/h and a summer high of 50 km/h.
• In the crest and trough of the jet stream, the maximum wind velocity is measured.

Types of Jet streams

The Jet Streams are of the following types:

Polar Front Jet Streams

• They form above the convergence zone of the surface polar cold air mass and tropical warm air mass (40 degrees and 60 degrees latitude).
• Since two contrasting air masses have collided, the thermal gradient is steep.
• These have a more variable position than the subtropical jet and move in an easterly direction.

Subtropical Westerly Jet streams

• They move north of the subtropical high-pressure belt in the upper troposphere in both hemispheres above 30 degrees to 35 degrees latitude.
• Their circulation is more regular than the polar front jet stream, and it moves from west to east.
• It is produced by the earth's rotation and flows for the majority of the year.

Tropical Easterly Jet Streams

• This is an upper-level easterly wind that begins in late June and lasts until early September.
• This strong upper-atmosphere flow that develops during the Asian monsoon is centred on 15°N, 50-80°E, and extends from Southeast Asia to Africa.
• The jet's strongest development occurs about 15 kilometres above the Earth's surface, over the Indian Ocean, with wind speeds of up to 40 metres per second.
• After the SubTropical Jet (STJ) has shifted to the north of the Himalayas, the Tropical Easterly Jet (TEJ) emerges (Early June).

Polar Night Jet Streams

• During the winter months, when the nights are much longer, the polar-night jet stream forms.
• During the summer, the polar night jet travels at a higher altitude (approximately 24,000 metres).
• The air high above the poles becomes much colder than the air over the Equator during these dark months.
• The polar night jets, which race eastward at an altitude of about 48 kilometres, are created by extreme air pressure differences in the stratosphere, which, when combined with the Coriolis effect, produce extreme air pressure differences in the stratosphere.

Local Jet Streams

• Local Jet Streams are locally formed as a result of local thermal and dynamic conditions.
• These Jet Streams are only of local significance.

Other Types

• Barrier Jets: In the low levels, a barrier jet forms just upstream of mountain chains, causing the jet to be oriented parallel to the mountains.
• Coastal Low- Level Jets: Coastal low-level jets are associated with a sharp contrast between high temperatures on land and lower temperatures at sea, and they play an important role in coastal weather, causing strong coast parallel winds. These are linked to oceanic high-pressure systems and land-based thermal lows.
• Valley Exit Jets: A valley exit jet is a strong, down-valley, elevated air current that flows above the valley's and adjacent plain's intersection. They have the ability to travel at high speeds and heights.
• African Easterly Jets: During the summer in the Northern Hemisphere, between 10°N and 20°N above West Africa, the mid-level African easterly jet occurs. The nocturnal poleward low-level jet occurs in East and South Africa's Great Plains.

How do Jet Streams affect the Indian climate?

• During the winter months, the westerly jet stream brings western cyclonic disturbances (originating over the Mediterranean Sea) that enter the Indian subcontinent from the west and northwest.
• The arrival of these cyclone disturbances is usually preceded by an increase in the prevailing night temperature.
• During the summer months, an easterly jet stream known as the sub-tropical easterly jet stream blows over peninsular India, passing over 14°N.
• Tropical cyclones are part of the easterly flow and occur during the monsoon season as well as in October and November.
• These disturbances have an impact on the country's coastal regions.

Flow of Jet Streams In India

• Jet Streams flow along the southern slopes of the Himalayas in the winter and shift northwards in the summer, flowing along the Himalayan edge (early June).
• They also blow in late summer, between July and August, along the Tibetan Plateau's northern edge.
• 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 signalled by the subtropical stream moving northward.

Significance of Jet Streams

• They have a significant impact on local and regional weather patterns.
• Temperate cyclones and jet streams have a close relationship in terms of intensity.
• Temperate cyclones and jet streams have a close relationship in terms of intensity.
• Jet streams collide with surface wind systems, resulting in severe storms.
• They also assist in providing a relatively clear picture of the occurrence of El Nino and La Nina events.
• Aviators use them as well if they have to fly in the direction of the jet stream's flow.
• When flying in the opposite direction of the jet streams, however, aviators avoid them because jet streams are unpredictable and can cause sudden movement even when the weather appears calm and clear.

Conclusion

South Asia's monsoon is largely influenced and controlled by jet streams. The upper air circulation, which is dominated by SubTropical Jet Streams, is also important for the monsoons. 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.

FAQs

Q1: What are jet streams?

Q2: Where are jet streams typically located?

Q3: How do jet streams influence weather?

Q4: What is the role of jet streams in aviation?

Q5: How do jet streams affect the Indian monsoon?

MCQs

1. Jet streams are typically located in which layer of the atmosphere?

a) Troposphere

b) Stratosphere

c) Tropopause

d) Mesosphere

2. What is the primary factor responsible for the formation of jet streams?

a) Ocean currents

b) Temperature and pressure differences

c) Earth's rotation

d) Solar radiation

3. Which of the following jet streams has a significant impact on the Indian monsoon?

a) Polar jet stream

b) Subtropical jet stream

c) Mid-latitude jet stream

d) Arctic jet stream

4. How do jet streams impact aviation?

a) They prevent air travel during storms.

b) They increase flying time due to turbulence.

c) They provide tailwinds that reduce fuel consumption and flying time.

d) They only affect low-altitude flights.

5. Which of the following is a consequence of jet streams influencing weather patterns?

a) Constant warm weather

b) Sudden changes in weather conditions

c) Decreased precipitation

d) Increased seismic activity

GS Mains Questions and Model Answers

Q1. Discuss the role of jet streams in shaping global weather patterns.

Answer: Jet streams play a critical role in shaping global weather patterns by influencing the movement of air masses, pressure systems, and weather fronts. These fast-moving currents, located in the tropopause, act as boundaries between air masses of different temperatures. The polar jet stream, for example, separates the cold polar air from the warmer air to the south, while the subtropical jet stream influences the distribution of monsoon and trade winds. Jet streams also steer cyclonic storms and affect the formation of weather systems such as low-pressure depressions and anticyclones. Due to their ability to move weather systems rapidly across regions, jet streams can cause sudden weather changes and influence phenomena such as heat waves and cold spells. They also play a significant role in aviation, helping to reduce flight times and fuel consumption for planes traveling with the tailwind of the jet stream.

Q2. Analyze the influence of jet streams on the Indian monsoon system.

Answer: Jet streams have a profound influence on the Indian monsoon system, particularly the subtropical jet stream, which affects the timing, intensity, and distribution of monsoon rainfall across the subcontinent. During the summer months, the subtropical jet stream moves northward, allowing the southwest monsoon winds to advance into India. The positioning of the jet stream is crucial for determining the onset of the monsoon and its subsequent progress over the Indian subcontinent. Conversely, during the winter months, the jet stream shifts southward, facilitating the retreat of the monsoon and the onset of the northeast monsoon. Variations in the jet stream's strength and position can lead to monsoon irregularities, such as delayed rainfall, droughts, or excessive flooding, highlighting the critical role of jet streams in shaping India's agricultural productivity and water resources.

Q3. Examine the impact of polar and subtropical jet streams on regional climates in North America and Asia.

Answer: Polar and subtropical jet streams have a significant impact on the regional climates of North America and Asia by influencing the movement of weather systems and creating varying weather conditions. In North America, the polar jet stream often acts as a boundary between cold Arctic air and warmer air masses to the south. During winter, when the polar jet moves southward, it brings cold air into the United States and Canada, leading to cold spells and snowstorms. In contrast, when the jet stream moves northward, it allows warmer air to move in, resulting in heat waves and dry conditions.
In Asia, the subtropical jet stream plays a pivotal role in shaping the monsoon system. The movement of the subtropical jet during summer allows the southwest monsoon to bring rain to the Indian subcontinent, while its retreat in winter leads to dry conditions and the onset of the northeast monsoon. The strength and position of these jet streams directly affect weather extremes, such as droughts or heavy rainfall, and influence agricultural productivity and water availability in these regions.

Previous Year Questions on  Jet Streams

1. UPSC CSE Mains 2018

Question. Explain the role of jet streams in the formation of temperate cyclones.

Answer: Jet streams play a crucial role in the formation and development of temperate cyclones by influencing the movement of air masses and creating favorable conditions for cyclonic systems. A temperate cyclone typically forms along the polar front, where cold polar air meets warmer tropical air. The polar jet stream, which flows along the polar front, helps to deepen areas of low pressure, leading to the development of a cyclonic circulation. The jet stream's strong winds can also enhance the rotation of air, further intensifying the cyclone. Additionally, the jet stream helps to steer the cyclone across regions, influencing its path and intensity. These cyclones are characterized by strong winds, heavy rainfall, and storm surges, making jet streams a key factor in shaping mid-latitude weather patterns.

2. UPSC CSE Mains 2019

Question. Discuss the impact of jet streams on the Indian monsoon and its variability.

Answer: Jet streams, particularly the subtropical jet stream, have a significant impact on the Indian monsoon and its variability. The southwest monsoon, which brings the majority of India's annual rainfall, is heavily influenced by the movement of the subtropical jet stream. In summer, the jet stream moves northward, allowing the southwest monsoon winds to advance over the Indian subcontinent. Any changes in the position or strength of the jet stream can lead to variations in the onset, intensity, and distribution of monsoon rainfall. For instance, if the jet stream is positioned farther north than usual, it can cause a delay in the monsoon's arrival, leading to drought conditions in some areas. Conversely, an intense jet stream can result in heavy rainfall and flooding. The variability of the Indian monsoon, therefore, is closely linked to the behavior of the jet streams, making it a crucial element in monsoon forecasting and agricultural planning.