What is the mechanism of the Indian monsoon? What are the classical and modern theories? What is the role Inter-Tropical Convergence Zone in monsoon? Read further to know more.
The “monsoon” climate is related to the seasonal reversal of wind direction. The monsoons are a seasonal wind pattern that travels from the sea to the land in the summer and from the sea to the land in the winter.
The Indian subcontinent, central-western Africa, Southeast Asia, and a few other regions all have monsoons, but the winds are highest in the Indian subcontinent.
The Indian monsoon accounts for over 70% of India’s annual rainfall.
India’s climate, like that of South and Southeast Asia, is hot and humid during the monsoon season. Monsoon seasons account for two of the four seasons that exist on the Indian subcontinent. They are
- The Southwest Monsoon Season
- The North-East Monsoon Season
The name monsoon is derived from the Arabic word mausin or the Malayan word monsin, both of which means season. Monsoons are seasonal winds (rhythmic wind movements) (periodic winds) that reverse direction as the seasons change. The monsoon is a seasonal wind pattern that flows from sea to land in the summer and from land to sea in the winter. Some scholars consider monsoon winds to be large-scale land and marine breezes.
- Monsoons are unique to the Indian subcontinent, South East Asia, and sections of Central Western Africa, among other places.
- They are more noticeable in the Indian Subcontinent than in any other place.
- Convection cells on a massive scale characterise Indian monsoons.
- These are seasonal reversals in wind direction that occur on a regular or seasonal basis.
- In the summer, India receives southwest monsoon winds, while in the winter, it receives northeast monsoon winds.
- South-west monsoons arise as a result of an intense low-pressure system that forms over the Tibetan plateau.
- High-pressure cells over the Tibetan and Siberian plateaus are related to the northeast monsoons.
- The southwest monsoons deliver heavy rains to most of India, while the northeast monsoons bring rain to the country’s south-eastern coast (The southern coast of Seemandhra and the coast of Tamil Nadu.).
Mechanism of Indian Monsoon
Monsoons are not completely understood. Many ideas have been proposed to explain the mechanics of monsoons. The mechanism of the Indian monsoon which transforms vast sections of India from semi-desert to lush greenery still not completely known.
- The Rig Veda, for example, mentions monsoons. Yet, the monsoon mechanism was not mentioned in these books.
- Arab traders conducted the first scientific research on monsoon winds.
- Arab traders exploited the maritime route to trade with India, and monsoon patterns were critical to their success.
- Al Masudi, an Arab explorer, described the reversal of ocean currents and the monsoon winds over the north Indian Ocean in the tenth century.
- Sir Edmund Halley explained the monsoon in the seventeenth century as a result of thermal disparities between continents and oceans caused by differential heating.
Aside from differential heating, the formation of the monsoon is determined by the geometry of the continents, orography (mountains), and the characteristics of upper troposphere air circulation (jet streams). As a result, Halley’s idea has lost most of its relevance, whereas modern hypotheses based on air masses and jet streams are growing more important.
Classical Theory: Sir Edmund Halley’s Theory
Classical theory is based on summer monsoons and winter monsoons.
- The apparent route of the sun in summer is vertically above the Tropic of Cancer, resulting in high temperatures and low pressure in Central Asia.
- The pressure is high enough across the Arabian Sea and the Bay of Bengal. As a result, in the summer, winds streamed from the oceans towards the mainland.
- This airflow from the sea to the land brings significant rain to the Indian subcontinent.
- The sun’s apparent path in winter is vertically over the Tropic of Capricorn.
- The northwestern section of India becomes colder than the Arabian Sea and the Bay of Bengal, and the monsoon flow is reversed.
- The essential concept underpinning Classical theory is similar to the production of land and sea breezes, except that in the case of monsoons, day and night are substituted by summer and winter.
Monsoons do not develop evenly everywhere on Earth, and Halley’s thermal notion fails to describe the complexities of monsoons such as sudden bursts of monsoons, occasionally a delay in one set of monsoons, and so on.
Modern theory: Air Mass Theory
According to this view, the monsoon is just a modification of the tropics’ planetary winds. The notion is based on the seasonal migration of the ITCZ.
Role of ITCZ [Inter-Tropical Convergence Zone]
- Near the equator, the southeast trade winds of the southern hemisphere and the northeast trade winds of the northern hemisphere meet.
- The Inter-Tropical Convergence Zone is where these winds collide (ITCZ).
- This is the area of ascending air, the greatest clouds, and heavy rainfall.
- During the changing of the seasons, the location of the ITCZ varies north and south of the equator.
- During the summer, the sun shines vertically over the Tropic of Cancer, and the ITCZ shifts northward.
- Under the influence of Coriolis force, the southern hemisphere’s southeast trade winds cross the equator and begin blowing southwest to northeast.
- As these displaced trade winds blow over the Indian subcontinent, they are known as south-west monsoons.
- The Monsoon Front is the boundary between the south-west monsoons and the north-east trade winds (ITCZ). Along this front, rain falls.
- The ITCZ shifts to 20°- 25° N latitude in July, where it is positioned in the Indo-Gangetic Plain, and the south-west monsoons blow from the Arabian Sea and the Bay of Bengal. In this position, the ITCZ is referred to be the Monsoon Trough [highest rainfall].
- Because of the seasonal change of the ITCZ, the notion of Northern Inter-Tropical Convergence Zone (NITCZ) in summer (July – rainy season) and Southern Inter-Tropical Convergence Zone (SITCZ) in winter has emerged (Jan – dry season).
- The NITCZ is the cloud and rainfall zone that affects India.
Also Read: Seasons in India – ClearIAS
Onset of the Monsoon
- In April and May, when the sun shines vertically over the Tropic of Cancer, the huge continent to the north of the Indian Ocean gets exceedingly hot.
- This causes an intense low-pressure system to build in the northwestern section of the subcontinent.
- Because the pressure in the Indian Ocean to the south of the landmass is high due to the slow heating of water, the low-pressure cell attracts southeast trades over the Equator.
- These factors help the ITCZ to move northward.
- The southwest monsoon can be considered as a continuation of the southeast trades deflected towards the Indian subcontinent after crossing the Equator.
- These winds cross the Equator between 40°E and 60°E longitudes.
- The southwest monsoon arrives on the Kerala coast on June 1st and sweeps fast through Mumbai and Kolkata from June 10th to June 13th.
- By mid-July, the southwest monsoon has engulfed the whole subcontinent.
The Southwest Monsoon Season
- The Rainy Season is from June to September.
- Low-pressure conditions in the northwest plains have gotten even more extreme as a result of the quick rise in temperature in May.
- By early June, they are strong enough to attract Southern Hemisphere trade winds from the Indian Ocean.
- These southeast trade winds traverse the equator, entering the Bay of Bengal and the Arabian Sea before becoming entangled in the air circulation over India.
- As they move through the equatorial warm currents, they bring a lot of moisture with them.
- After passing through the equator, they head southwest. This is what the southwest monsoons are called.
Bursts of the Southwest Monsoon
- During the southwest monsoon season, the rain begins suddenly.
- The first rain has a substantial cooling effect on the temperature.
- The term “monsoon break” or “burst” refers to the abrupt onset of moisture-laden winds accompanied by strong thunder and lightning.
- The monsoon may come in the first week of June in coastal parts of Kerala, Karnataka, Goa, and Maharashtra, and in the first week of July in the interior.
- The daily temperature drops by 5°C to 8°C between mid-June and mid-July.
- As these winds approach the land, the relief and thermal low pressure over northwest India change their southwesterly course.
- The northeast monsoon makes its way into India from the northeast.
- With this type of monsoon, the wind blows from the sea to the land.
- The monsoon winds transport moisture from the Indian Ocean.
- From October through December, the northeast monsoon is limited to south India, bringing rain to Tamil Nadu, Puducherry, Karaikal, Yanam, Andhra Pradesh, Kerala, Mahe, and south interior Karnataka.
- The related rainfall, often known as the winter monsoon, is caused by low-pressure systems, depressions, and cyclones.
- This is Tamil Nadu’s main rainy season, with 48% (447.4mm) of the state’s annual rainfall falling during these three months.
Season of Retreating Monsoon
- Monsoons are known to disappear between October and November.
- The southwest monsoon weakens around the end of September as the Ganga plain’s low-pressure trough begins to travel southward in reaction to the sun’s southward march.
- The monsoon has left western Rajasthan by the first week of September.
- It will have passed across Rajasthan, Gujarat, the Western Ganga plain, and the Central Highlands by the end of the month.
Effects caused by Retreating Monsoons
- These tropical cyclones pose a significant risk.
- The thickly populated deltas of the Godavari, Krishna, and Kaveri rivers are their favoured targets.
- Every year, devastating cyclones wreak havoc on this region.
- Cyclonic storms have also slammed the shores of West Bengal, Bangladesh, and Myanmar.
- The majority of the rainfall on the Coromandel coast is caused by these depressions and cyclones.
- Such cyclonic storms are less common in the Arabian Sea.
Importance of the Indian Monsoon
- Because about 60% of India’s net arable land lacks irrigation, the monsoon is crucial for agriculture.
- The monsoon is responsible for over 70% of India’s annual rainfall and influences the yield of a wide range of cereals and pulses, including rice, wheat, and sugarcane.
- Agriculture employs more than half of India’s people, and monsoon rains have a direct impact on their wages and well-being.
- Agriculture contributes to more than 15% of India’s GDP, hence crop failure due to a lack of rain has a negative impact on the economy.
- Monsoonal rainfall helps with water storage for irrigation, electricity generation, and drinking.
The effect of the monsoon on local weather varies depending on location. Some areas may have a bit more or less rain. Semi-deserts in other areas are turned into beautiful green grasslands that support a varied range of flora and crops. The Indian Monsoon converts enormous areas of India from semi-desert to lush greenery. Farmers in regions like this must have the proper timing for spreading seeds on the fields since it is vital to use all of the available rain to grow crops.
Article Written By: Atheena Fathima Riyas