Jet Streams: Subtropical Westerly and Tropical Easterly Jets, Rossby Waves and their Role in Indian Weather (UPSC Notes + PYQs)
UPSC has already asked about this. Read the story with these questions in mind.
How they form
Strong temperature contrasts between air masses create steep pressure gradients aloft; the Earth’s rotation (Coriolis force) turns the flow into west-to-east bands. They occur in both hemispheres, which a 2020 Prelims question tested.
Types relevant to India
- Subtropical westerly jet (STWJ): around 30°N in winter, splits around the Tibetan plateau; the southern branch sits over north India and brings western disturbances that give winter rain in Punjab and snow in the Himalayas, valuable for rabi wheat.
- Tropical easterly jet (TEJ): forms in summer over peninsular India at about 15°N when the Tibetan plateau heats the upper air.
- Polar front jet: mid-latitudes, steers mid-latitude cyclones.
The monsoon link
In early June, the westerly jet jumps north of the Himalayas. The easterly jet then establishes itself over the peninsula, and the monsoon bursts. A late shift of the westerly jet delays onset. When the jet returns south in October, the monsoon retreats.
Rossby waves and extreme weather
Jets meander in large loops called Rossby waves. When the loops stall, heat waves or floods can persist; the 2010 Russian heat wave and Pakistan floods were linked to such a blocking pattern. A warming Arctic may be weakening the polar jet.
Jet Streams: UPSC angle
For UPSC CSE
Prelims: location, direction, both hemispheres, link to monsoon and western disturbances. Mains GS-I: mechanism of Indian monsoon; extreme weather.
Jet Streams UPSC PYQs (Prelims)
Questions UPSC has actually asked, from the official papers. Pick an option to check yourself.
Consider the following statements :
– 1. Jet streams occur in the Northern Hemisphere only.
– 2. Only some cyclones develop an eye.
– 3. The temperature inside the eye of a cyclone is nearly 10°C lesser than that of the surroundings.
Which of the statements given above is/are correct ?
Jet streams blow in both hemispheres. Only mature, strong tropical cyclones develop a clear eye, and temperate cyclones have none. Sinking air makes the eye warmer than its surroundings, by as much as 10 °C, not colder. Answer as per the official UPSC key · Battle IAS PYQ bankAnswer (c) & why
Mains PYQs on this topic
No UPSC Mains question from 2023-2026 is directly on this topic. Older papers (2013-2022) will be added as the Mains bank grows.
Quick quiz
Jet streams occur
UPSC 2020.Answer (b)
The tropical easterly jet over India appears in
It is linked to Tibetan heating.Answer (b)
Western disturbances are brought to north India by the
In winter.Answer (b)
FAQs
At what height do jet streams blow?
In the upper troposphere, roughly 9-14 km above the surface.
What are western disturbances?
Low-pressure systems from the Mediterranean region carried east by the westerly jet, bringing winter rain and snow to north India.
How do jet streams affect flights?
Eastbound flights save time riding the westerlies; westbound flights avoid them.
What is a Rossby wave?
A large meander in the jet stream.
Spotted an error? Tell us. We correct within 48 hours.
Image: https://commons.wikimedia.org/wiki/File:Jet_Stream_Convergence.jpg
How to use this in Mains
If asked: Explain the role of jet streams in the Indian monsoon. (GS-I)
Quote: “In early June, the westerly jet jumps north of the Himalayas.”
Use it: The key mechanism point in your body.
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