Consider the following statements :

The winds which blow between 30°N and 60°S latitudes throughout the year are known as westerlies.

The moist air masses that cause winter rains in North-Western region of India are part of westerlies

Which of the statements given above is/are correct?

Question

Consider the following statements :

The winds which blow between 30°N and 60°S latitudes throughout the year are known as westerlies.
The moist air masses that cause winter rains in North-Western region of India are part of westerlies

Which of the statements given above is/are correct?

Accepted Answer

2 only Quick Verdict: Statement 1 is incorrect because Westerlies do not blow continuously from 30°N across the equator down to 60°S; they are confined to the 30°–60° latitudinal belts in each hemisphere separately. Statement 2 is correct because India's winter rains are caused by Western Disturbances, which are driven by the upper-air westerly jet streams. Thematic Discussion: Planetary Winds and Western Disturbances The Domain of the Westerlies (Statement 1 - Incorrect) Planetary winds are strictly divided by latitudinal belts. The Westerlies blow from the subtropical high-pressure belts towards the sub-polar low-pressure belts. Crucially, they exist in two separate bands: between 30°N and 60°N in the Northern Hemisphere, and between 30°S and 60°S in the Southern Hemisphere. The area between 30°N and 30°S is dominated by the Trade Winds, not Westerlies. Western Disturbances and India's Winter Rains (Statement 2 - Correct) During the winter solstice in December, the global pressure and wind belts shift southward towards the equator. This shift brings the land areas of north-western India (between 30°-40°N) directly under the influence of the upper-air Subtropical Westerly Jet Stream. Why the Name? Because these weather systems originate in the west (the Mediterranean region) and travel eastward to "disturb" the normally calm, cool, and dry winter climate of north-western India, they are termed Western Disturbances. Origin and Path: The upper-air westerly jet stream acts as a conveyor belt, driving temperate cyclonic depressions from the Mediterranean region towards the Indian subcontinent. Moisture Augmentation: As these cyclonic waves (moist air masses) travel over land, their moisture content is significantly boosted as they pass over the Caspian Sea and the Persian Gulf. Impact on India: Upon reaching India, they cause critical winter rainfall in Punjab, Haryana, and Rajasthan, and snowfall in the Himalayan belt. Following these cyclonic waves, the region experiences widespread fog and cold waves that can drop temperatures by 5-10°C. Mains Concept Builder: Why is this rainfall "Orographic"? On average, 4 to 8 cyclonic waves reach north-western India between October and April. However, they lack the massive vertical cloud structures of summer monsoons. This is because descending high-pressure upper-air winds prevent these winter cyclonic waves from ascending beyond 200 meters, while surface trade winds cool them from below. Consequently, the precipitation they bring is largely orographic—forced upward and squeezed out by the physical barrier of the Himalayas. 📝 Mains Practice Question (GS Paper 1): Discuss the mechanism of Western Disturbances. How do they influence the winter weather and agricultural economy of North-Western India? (150 words, 10 marks)