As we know that the climate of India is described as the ‘monsoon’ type. It is so because the climate of India is strongly influenced by monsoon winds. The monsoons are experienced within the tropical area roughly between 20° N and 20° S.
From where the term ‘Monsoon’ Originated?
In the historic times, many sailors came to India for trade. They were one of the first to have noticed the phenomenon of the monsoon and get benefited from the reversal of the wind system while they came by sailing ships at the mercy of winds. The Arabs had also come to India as traders named this seasonal reversal of the wind system as ‘monsoon’.
Mechanism of the Monsoons
To understand the mechanism of the monsoons, the subsequent facts are important:
- Heating and Cooling of Land and Water: The differential heating and cooling of land and water create a low pressure on the landmass of India while the seas around experience comparatively high pressure.
- Inter Tropical Convergence Zone (ITCZ): The shift of the position of ITCZ in summer, over the Ganga plain (this is the equatorial trough normally positioned about 5°N of the equator. It is also referred to as the monsoon trough during the monsoon season).
- High-Pressure Zone over the Indian Ocean: The presence of the high-pressure zone approximately at 20°S over the Indian Ocean near east of Madagascar. The Indian Monsoon gets affected by the intensity and position of this high-pressure area.
- Heating of Tibetan Plateau: The Tibetan plateau gets intensely heated during summer, which results in strong vertical air currents and the formation of low pressure over the plateau at about 9 km above sea level.
- Movement of the Westerly Jet Stream: The movement of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer.
About Southern Oscillation (SO) and El Nino Southern Oscillations (ENSO)
Apart from the above mechanism of the monsoon, it has also been noticed that changes in the pressure conditions over the southern oceans also affect the monsoons. Generally, when the tropical eastern south Pacific Ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure. But in certain years, there’s a reversal within the pressure conditions and therefore the eastern Pacific has lower pressure as compared to the eastern Indian Ocean. This periodic change in pressure conditions is called as the Southern Oscillation (SO).
The difference in pressure over Tahiti located in the Pacific Ocean at 18°S/149°W and Darwin in northern Australia located in the Indian Ocean at 12°30’S/131°E is computed to predict the intensity of the monsoons. If the pressure differences were negative, it might mean below average and late monsoons. A feature connected with the SO is that the El Nino phenomenon during which a warm ocean current that flows past the Peruvian Coast, in place of the cold Peruvian current, every 2 to 5 years. Consequently, the changes in pressure conditions are connected to El Nino. Hence, the phenomenon is mentioned as ENSO (El Nino Southern Oscillations).
What is meant by the Onset of the Monsoon?
The Monsoon winds are not steady winds but are pulsating in nature. These were affected by different atmospheric conditions which were encountered on their way over the warm tropical seas. The monsoon takes place between 100-120 days from early June to mid-September. During the time of arrival of Monsoon, the normal rainfall increases abruptly and continues constantly for several days. This is referred to as the ‘burst’ of the monsoon and may be distinguished from the pre-monsoon showers.
What are the Branches of the Monsoon?
At the southern tip of the Indian peninsula, the monsoon hits generally by the first week of June. Subsequently, it proceeds into two branches:
- The Arabian Sea branch.
- The Bay of Bengal branch.
The Arabian Sea branch reaches Mumbai about ten days later or afterwards on approximately the 10th of June. This is a fairly rapid advance. The Bay of Bengal branch also advances rapidly and arrives in Assam within the first week of June. Due to the lofty mountains, the monsoon winds deflect towards the west over the Ganga plains. By mid-June, the Arabian Sea branch of the monsoon arrives over Saurashtra-Kuchchh region and thus moves towards the central part of the country. The Arabian Sea and therefore the Bay of Bengal branches of the monsoon merge over the northwestern part of the Ganga plains.
By the end of June, Delhi generally receives the monsoon showers from the Bay of Bengal branch. On the other hand western Uttar Pradesh, Punjab, Haryana and eastern Rajasthan experience the monsoon by the first week of July. Further, the monsoon reaches Himachal Pradesh and the rest of the country by the first week of July.
Know about the withdrawal or the Retreat of the Monsoon
Withdrawal or the retreat of the monsoon may be a more gradual process. By early September, the withdrawal of the monsoon begins in northwestern states of India. And by mid-October, it withdraws completely from the northern half of the peninsula. But the withdrawal from the southern half of the peninsula is fairly rapid.
The monsoon has withdrawn from the rest of the country, by early December. The very first monsoon showers are received by the islands, progressively from south to north and that too from the last week of April to the first week of May. From the first week of December to the first week of January, the withdrawal takes place progressively from north to south. By this time the rest of India is already under the influence of the winter monsoon.
How Monsoon act as a Unifying Bond?
As we know that the Himalayas protect the subcontinent from extremely cold winds from central Asia. This enables northern India to possess uniformly higher temperatures compared to other areas on equivalent latitudes. Similarly, the peninsular plateau has moderate temperatures. Despite such moderating influences, there are great variations within the temperature conditions. Nevertheless, the unifying influence of the monsoon on the Indian subcontinent is sort of perceptible. The seasonal alteration of the wind systems and therefore the associated weather conditions provide a rhythmic cycle of seasons.
Also, the uncertainties of rain and uneven distribution are very much typical of the monsoons. The entire life of Indian landscape whether animal and plant life, entire agricultural calendar and people’s life including festivities, etc. revolve around the Monsoon. Year after year, from north to south and from east to west, the people of India eagerly awaited for the arrival of the monsoon. These monsoon winds bind the entire country by providing water to line the agricultural activities in motion. The river valleys which carry this water also unite as a one or single river valley unit.
For Free UPSC Study Material And Counselling From Experts: Click Here
