Based on the following statements, select the correct answer from the code given below: (a) Western disturbances are driven by westerly winds. (b) Western disturbances bring moisture from the Mediterranean Sea. (c) They cause rainfall in the northwestern parts of India during the winter season.
- (a)Only (c) is correct
- (b)Only (a) and (c) are correct
- (c)Only (b) and (c) are correct
- (d)(a), (b) and (c) are correct
Correct — D, all three statements are correct. (a) A western disturbance is an extratropical low-pressure system that is steered from west to east by the westerlies, specifically by the subtropical westerly jet stream that sits over north India in winter. (b) These systems form over and around the Mediterranean and pick up their moisture there, adding more from the Caspian, the Black Sea and, closer to India, the Arabian Sea. (c) When they reach the western Himalaya they are forced to rise, and the result is winter rain over Punjab, Haryana, Delhi, western Uttar Pradesh and northern Rajasthan, with snow in Jammu and Kashmir, Ladakh, Himachal and Uttarakhand. The three statements are simply three stages of one chain, so nothing can be excluded.
- (a)Only (c) is correct — Rejects both the mechanism and the moisture source, though the westerly steering and the Mediterranean origin are the standard textbook description of a western disturbance.
- (b)Only (a) and (c) are correct — Drops statement (b). Students often doubt the Mediterranean because it feels too far away — but that region is precisely where these systems originate and take on moisture.
- (c)Only (b) and (c) are correct — Drops statement (a). Western disturbances travel west to east because the westerlies and the subtropical westerly jet carry them; without that steering they would never reach India.
A western disturbance is a mid-latitude (extratropical) cyclone, not a tropical one: it draws its energy from the temperature contrast along a front rather than from warm ocean water, and it is embedded in the westerly flow. Forming near the Mediterranean, it moves eastward across Iran, Afghanistan and Pakistan into north-west India, roughly between December and March, when the subtropical westerly jet has shifted south of the Himalaya. Its precipitation is the exact opposite of the monsoon in both season and direction of travel.
Because all three statements are true, the safe method is not to hunt for a false one but to test each independently: mechanism (westerlies), source (Mediterranean), effect (winter rain in the north-west). The trap for a hurried candidate is to assume that an 'all correct' option is too easy, or to confuse western disturbances with the retreating (north-east) monsoon, which is what rains on Tamil Nadu in October to December.
- Western disturbances are extratropical cyclones steered eastward by the westerlies and the subtropical westerly jet stream
- They originate over the Mediterranean region and gather moisture there, with additions from the Caspian, the Black Sea and the Arabian Sea
- They bring winter rain (locally called mahawat) to Punjab, Haryana, Delhi, western UP and north Rajasthan, and snow to the western Himalaya
- This winter rain is critical for rabi crops, above all wheat
- Their side effects include cold waves, dense fog, hailstorms and Himalayan avalanches; a weak season hurts rabi yields
- An extratropical low forms over the Mediterranean region and picks up moisture (statement b)
- The westerlies and the subtropical westerly jet steer it eastward over Iran, Afghanistan and Pakistan (statement a)
- The western Himalaya forces the air to rise — winter rain over Punjab, Haryana, Delhi, west UP and north Rajasthan; snow in J&K, Himachal and Uttarakhand (statement c)
- Rabi crops, especially wheat, benefit; cold waves, fog, hail and avalanches are the flip side
The three statements in the question are three links of a single chain — which is why the answer is 'all correct'.
- Believing western disturbances rain over all of India — their footprint is the north and north-west
- Confusing them with the retreating/north-east monsoon that brings October–December rain to Tamil Nadu
- Calling them tropical cyclones; they are extratropical systems driven by frontal contrasts
Usually a statement-based set on the mechanism, or a cause question ('winter rainfall in north-west India is due to'). UPSC 2015 tested the same idea through the westerlies. Remember the three anchors — westerly steering, Mediterranean moisture, rabi benefit.
Consider the following statements: 1. The winds which blow between 30° N and 60° S latitudes throughout the year are known as westerlies. 2. The moist air masses that cause winter rains in North-Western region of India are part of westerlies.
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer(b) 2 only — the moist air masses causing north-west India's winter rain are indeed part of the westerlies; statement 1 misstates the westerly belt, which lies between about 30° and 60° in each hemisphere.
Directly tests statement (a) of this MPPSC question — that the winter rain of north-west India is carried in by the westerlies.
- practice — not a real PYQ
Winter rainfall in the north-western plains of India is caused mainly by:
- (a)The south-west monsoon
- (b)The retreating monsoon
- (c)Western disturbances
- (d)Cyclones from the Bay of Bengal
Answer(c) Western disturbances — extratropical systems arriving from the Mediterranean side.
- practice — not a real PYQ
Which of the following best describes western disturbances?
- (a)Tropical cyclones forming over the Arabian Sea
- (b)Extratropical low-pressure systems steered by the subtropical westerly jet stream
- (c)Local convective thunderstorms of the Deccan plateau
- (d)Depressions that form over the Bay of Bengal in October
Answer(b) Extratropical low-pressure systems steered by the subtropical westerly jet stream.