Chapter 4

NCERT
Class 9
Geography
Solutions
6. Discuss the mechanism of monsoons.

Question:

Discuss the mechanism of monsoons.

Answer:

The monsoons are experienced in the tropical area roughly between 20° N and 20° S. The Arabs, who came to India as traders named this seasonal reversal of the wind system 'monsoon'. To understand the process of the monsoons, the following facts are important:

(i) The low pressure on the landmass of India is created by the differential heating and cooling of land and water while comparative high pressure is felt due to the seas around.

(ii) InterTropical Convergence Zone (ITCZ) in summer shifts the position over the Ganga plain. This is the equatorial trough normally positioned about 5°N of the equator. During the monsoon season, it is also known as the monsoon trough.

(iii) The presence of the high-pressure area, east of Madagascar, approximately at 20°S over the Indian Ocean affects the Indian Monsoon.

(iv) The Tibetan plateau gets intensely heated during summer due to which strong vertical air currents and low pressure is formed over the plateau at about 9 km above sea level.

(v) During summer there is a movement of the westerly jet stream to the north of the Himalayas. At the same time, there is the presence of the tropical easterly jet stream over the Indian peninsula during summer.

(vi) The difference in pressure over Tahiti (Pacific Ocean, 18°S/149°W) and Darwin in northern Australia (Indian Ocean, 12°30'S/131°E) is computed to predict the intensity of the monsoons. If there are negative pressure differences, then it indicates below average and late monsoon.

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