Jet Streams and Their Impact on India's Weather

Jet Streams - Meaning, Types, Effects on Indian Weather

We often hear the term "jet streams" in weather reports, but what are they really? These fast-moving winds high up in the sky have a big impact on our weather, even though we can’t see them. In India, jet streams affect everything from the arrival of monsoon rains to winter cold waves. Understanding them helps us make sense of many weather changes we see every year. Let’s take a closer look at what jet streams are and how they affect our weather.



What are jet streams?

"Jet streams are strong winds blowing high above Earth's surface, in the upper troposphere. They usually flow from west to east in both hemispheres. Most of the time, their speeds are around 129 to 225 kilometers per hour (80 to 140 miles per hour), but sometimes they can go as fast as 443 kilometers per hour (275 miles per hour). During winter, these jet streams become even faster, because the difference in temperature between warm and cold air becomes bigger."

 How did they form?

"Jet streams primarily form due to significant temperature differences. However, other factors such as pressure gradients and the Coriolis effect also play crucial roles. When warm and cold air masses meet, they create fronts. In the upper troposphere, these interactions result in the formation of jet streams.The warmer air rises because it's lighter, while the cooler, heavier air sinks downwards. This vertical movement creates differences in pressure, leading air to move from areas of high pressure to areas of low pressure. As Earth spins, it causes these moving winds to curve and flow horizontally instead of straight. Together, all these actions produce strong, narrow bands of fast-moving air we call jet streams."

Types of Jet Streams

There are mainly four types of jet streams. Out of these, two are permanent (present throughout the year) and two are seasonal (appear only during specific times of the year).
The permanent ones are the Polar Jet Stream and the Subtropical Jet Stream, while the seasonal ones are the Tropical Easterly Jet Stream and the Polar Night Jet Stream.


1.Polar Jet Stream (Permanent)

  • Found near the polar front, where cold polar air meets warmer air from temperate regions.

  • Located between 50° to 60° latitudes in both hemispheres.

  • Strongest in winter due to bigger temperature differences.

  • Affects weather in temperate regions like Europe, North America, and parts of Asia.

2. Subtropical Jet Stream (Permanent)

  • Found around 30° latitude in both hemispheres, near the subtropical high-pressure zone.

  • Forms due to the sinking air of the Hadley Cell and temperature contrast at high altitudes.

  • Flows at high altitudes and is usually slower than the polar jet.

  • Plays a role in steering monsoon systems and influencing weather patterns in tropical and subtropical areas.

3. Tropical Easterly Jet Stream (Seasonal)

  • Appears only during the Indian summer monsoon season (June to September).

  • Flows from east to west (unlike others that flow west to east).

  • Found near 15°N to 20°N latitude, mainly over South Asia and Africa.

  • Helps in strengthening the southwest monsoon over India.

4. Polar Night Jet Stream (Seasonal)

Found in polar regions during winter, especially in the upper stratosphere.

  • Forms due to extremely cold polar air and lack of sunlight during polar night.

  • Located above the Polar Jet Stream, and weaker compared to it.

  • Disappears or weakens as sunlight returns in spring.

Characteristics of Jet Streams

  1. High-Speed Winds:
    Jet streams are very fast-moving winds. Their speeds usually range between 129 to 225 km/h, but they can go over 443 km/h.

  2. Found in the Upper Troposphere:
    They flow at high altitudes, around 8 to 15 km above the Earth's surface, just below the stratosphere.

  3. Flow from West to East:
    Most jet streams flow from west to east due to the Earth’s rotation and the Coriolis effect.

  4. Stronger in Winter:
    Jet streams become more intense during winter, when temperature differences between regions are greater.

  5. Meander Like Rivers (Rossby Waves):
    Jet streams do not move in a straight line—they meander or bend, forming waves called Rossby waves.

  6. Influence Weather and Climate:
    Jet streams play a major role in controlling weather systems, such as storms, rainfall, and cold waves.


How Jet Streams Affect Indian Weather:

Jet streams play an important role in shaping the weather in India. Their position and strength help decide whether we get rain, dry weather, cold waves, or even heatwaves.

1. Monsoon (Rainy Season)

  • During summer (June to September), the Tropical Easterly Jet Stream forms over India.

  • This jet stream helps pull the monsoon winds (moist winds from the sea) deep into the land, bringing heavy rainfall.

  • If this jet stream is strong, the monsoon is usually good. If it is weak, the rains may be delayed or reduced.

2. Western Disturbances (Winter Rains)

The Polar Jet Stream, also called the Westerly Jet Stream in this context, is responsible for bringing Western Disturbances to India.

  • The Polar Jet Stream flows from west to east in the upper troposphere, mainly over mid-latitudes (around 30° to 60°N).

  • In winter, this jet stream shifts southward and brings moist air from the Mediterranean Sea toward North India.

  • These winds carry Western Disturbances, which are low-pressure systems that bring rain and snowfall to Jammu & Kashmir, Himachal Pradesh, Punjab, Haryana, and sometimes Delhi.

3. Cold Waves in North India

  • When the polar jet stream dips more than usual, it brings cold winds from the Himalayas to the plains.

  • This causes cold wave conditions in states like Delhi, UP, and Bihar during December–January.

4. Heatwaves in Summer (Caused by Subtropical Jet Stream)

  • During the pre-monsoon summer months (especially April to June), the Subtropical Jet Stream plays an important role in Indian weather.

    Sometimes, this jet stream shifts northward or gets stuck in one position (called a blocking pattern). When this happens:

    • It prevents clouds and rain-bearing winds from reaching central and northern India.

    • As a result, the sky stays clear for many days.

    • With no rain or cloud cover, the land heats up quickly under the sun.

    This leads to severe heatwaves, especially in regions like Rajasthan, Delhi, Madhya Pradesh, Uttar Pradesh, and Bihar, where temperatures can go above 45°C.


Conclusion

Jet streams may be invisible, but their impact on India’s weather is powerful and far-reaching. From guiding monsoons to triggering cold waves and heat waves, they quietly shape our seasons. Understanding jet streams helps us not only make sense of changing weather patterns but also prepare better for what lies ahead.


📝 UPSC Prelims PYQs on Jet Streams

🔹 Prelims 2015 (Conceptual Relevance)

Q. With reference to the Indian climate, consider the following statements:

  1. The western disturbances originate in Iran and Afghanistan.

  2. They are brought into India by the subtropical westerly jet stream.

Which of the statements given above is/are correct?
a) 1 only
b) 2 only
c) Both 1 and 2
d) Neither 1 nor 2
✅ Answer: c) Both 1 and 2

📄 UPSC Mains PYQs on Jet Streams

🔸 Mains 2013 – GS Paper I

Q. Bring out the relationship between the southwest monsoon and the Tropical Easterly Jet Stream (TEJ).

🔸 Mains 2021 – GS Paper I

Q. Examine the role of jet streams in bringing about the western disturbances which cause winter rainfall in the north-western parts of India.


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