Nature and origin of Indian monsoon and recent techniques of its prediction

Question – Discuss the nature and origin of Indian monsoon and recent techniques of its prediction. – 30 November 2021

Answer – Monsoon is a global phenomenon that occurred between 20 degrees north and south. The word ‘monsoon’ has been derived from the Arabic word ‘Mausim’ which means ‘season’. Originally, this word was used by Arab traders to describe a system of seasonal reversal of winds along the shores of the Indian Ocean.

Origin of Indian monsoon: 

Monsoon is a complex meteorological phenomenon. Experts of meteorology have developed a number of concepts about the origin of the monsoon. Some of them are as follows-

• Thermal Concept: According to this, the primary cause of the annual cycle of the Indian monsoon circulation is the differential heating effects of the land and the sea.
• Besides differential heating, the development of monsoon is influenced by the shape of the continents, orography (mountains), and the conditions of air circulation in the upper troposphere {jet streams}.
• According to modern theory, the monsoon is simply a modification of the planetary winds of the tropics. The theory is based on the migration of ITCZ based on seasons.
• The southeast trade winds in the southern hemisphere and the northeast trade winds in the northern hemisphere meet each other near the equator.
• The meeting place of these winds is known as the Inter-Tropical Convergence Zone (ITCZ). This is the region of ascending air, maximum clouds and heavy rainfall.
• The location of ITCZ shifts north and south of equator with the change of season. In the summer season, the sun shines vertically over the Tropic of Cancer and the ITCZ shifts northwards.
• The southeast trade winds of the southern hemisphere cross the equator and start blowing in southwest to northeast direction under the influence of Coriolis force.
• The front where the south-west monsoons meet the north-east trade winds is known as the Monsoon Front (ITCZ). Rainfall occurs along this front.
• In the month of July the ITCZ shifts to 20°- 25° N latitude and is located in the Indo-Gangetic Plain and the south-west monsoons blow from the Arabian Sea and the Bay of Bengal. The ITCZ in this position is often called the Monsoon Trough.

 Nature of Indian Monsoon:

Systematic studies of the causes of rainfall in the South Asian region help to understand the salient features of the monsoon, particularly some of its important aspects, such as:

1. These winds generally strike the Indian coast in the first week of June but their arrival and departure may be before time or even it may be delayed.
2. There may be dry spells in between rainy periods. Such long dry spells may even lead to failure of crops.
3. At times, these winds skip over certain regions without any cause.
4. The amount and timing of rainfall and intervening duration of wet and dry spells varies from year to year. This is known as the vagaries of the monsoons.
5. The spatial distribution of rainfall is uneven – some regions may receive heavy rains while the others will have to be contented with meager or scanty rains.
6. Generally, these winds start retreating by the end of September. But, sometimes, their departure may be delayed till October or they may retreat even much earlier.

Recent technique in prediction of monsoon: 

The phenomenon of Monsoon is very important from the socio-economic point of view of the country. So its prediction has been very important. IMD has been using the regression model to predict monsoon over the years. But recently a dynamic model has been developed to predict monsoon. In this model, simulation is used to extrapolate the data obtained from various metrological station to a particular time frame. But still the technique is not full proof and so IMD has been providing predictions from both the models and using a coupled model forecast for Monsoon.

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