Indian Monsoon – Geography – UGC NET – Notes

The term “monsoon” refers to the climate associated with the seasonal reversal of wind direction. The monsoons are a double system of seasonal winds that travel from the sea to the land in the summer and from the land to the sea in the winter. Monsoons can be found in the Indian subcontinent, central-western Africa, Southeast Asia, and a few other places, but the winds are strongest in the Indian subcontinent. The Indian monsoon is responsible for approximately 70% of India’s annual rainfall. 

• The climate in India is hot monsoonal, as is the climate in South and Southeast Asia.
• Out of four seasons prevailing in the Indian subcontinent, monsoon seasons acquire two. They are
• The Southwest Monsoon Season
• The North-East Monsoon Season

Onset of the Monsoon

• When the sun shines vertically over the Tropic of Cancer in April and May, the large landmass to the north of the Indian Ocean becomes extremely hot.
• In the northwestern part of the subcontinent, this results in the formation of an intense low-pressure system.
• The low-pressure cell attracts southeast trades across the Equator because the pressure in the Indian Ocean to the south of the landmass is high due to the slow heating of water.
• These conditions aid in the ITCZ northward shift in position.

• After crossing the Equator, the southwest monsoon can be seen as a continuation of the southeast trades deflected towards the Indian subcontinent.
• Between 40°E and 60°E longitudes, these winds cross the Equator.
• The southwest monsoon arrives on the Kerala coast on June 1st and moves quickly through Mumbai and Kolkata between June 10th and 13th.
• The southwest monsoon engulfs the entire subcontinent by mid-July.

The Southwest Monsoon Season

• The Rainy Season is from June to September.
• As a result of the rapid rise in temperature over the northwestern plains in May, the low-pressure conditions there have become even more intense.
• They are powerful enough to attract the Southern Hemisphere trade winds coming from the Indian Ocean by early June.
• These southeast trade winds cross the equator and enter the Bay of Bengal and the Arabian Sea, only to become entangled in the air circulation over India.
• They bring a lot of moisture with them as they pass over the equatorial warm currents.
• They travel in a southwesterly direction after crossing the equator. Southwest monsoons are named after this.

The direction of Southwest Monsoon in India

Southwest Monsoon Bursts

The Southwest Monsoon is the rainy season that lasts from June to September. The Southwest Monsoon is the Indian subcontinent’s primary rainy season. The southwest monsoon holds over the country during the summer monsoon season. During this time, the country receives nearly 75% of its annual rainfall.

• The Southwest Monsoon Season, also called Rainy Season, is from June to September.
• This southwest monsoon is caused by an intense low-pressure system forming over the Tibetan Plateau as a result of intense heating during the summer season.
• They bring a lot of moisture with them as they pass over the equatorial warm currents.
• The rain begins when these winds hit or strike the mountain barriers.
• These southeast trade winds cross the equator and enter the Bay of Bengal and the Arabian Sea, only to become entangled in the air circulation over India.
• They travel in a southwesterly direction after crossing the equator. Southwest monsoons are named after this.
• Most parts of the country experience heavy rainfall due to the monsoon season winds.

Southwest Monsoon Winds in India

Temperature during Southwest Monsoon Season

• The onset of the South West Monsoons causes a significant temperature drop [3° to 6°C].
• During the rainy season, the temperature is less uniform.
• With the end of the southwest monsoons, the temperature rises in September.
• Whenever there is a break in the monsoons, the temperature rises.
• Due to clouds and rain, the diurnal temperature range is small.
• West of the Aravali, the highest temperatures [38° to 40°C] can be found. Due to a lack of clouds and warm continental air masses, this is the case.
• Temperatures in other parts of Northwest India are also above 30°C.
• Due to heavy rainfall, temperatures in the Western Ghats are quite low.
• Temperatures in the coastal areas of Tamil Nadu and adjoining parts of Andhra Pradesh are above 30°C due to the lack of rainfall during this season.

Pressure and Winds During South West Monsoon Season

• Due to the high temperature, low pressure prevails over northwest India.
• The Ganga plain is home to the ITCZ (monsoon trough). Its location is subject to frequent changes depending on the weather.
• The atmospheric pressure continues to rise as it moves southward.
• Winds from the Arabian Sea and the Bay of Bengal blow southwest to northeast over the peninsular region due to a pressure gradient between north and south.
• In the Indo-Gangetic plain, where they move from east to west, their direction changes.

Rainfall During South West Monsoon Season

• This season receives three-quarters of the total annual rainfall.
• This season, the average rainfall across India’s plains is around 87 percent.
• In the Andaman and Nicobar Islands, the monsoon usually arrives on the 20th of May.
• The monsoon moves much faster in the Bay of Bengal than it does in the Arabian Sea.
• The onset of the southwest monsoon over Kerala, i.e. the first point of entry into India’s mainland, is usually on June 1st.
• The monsoons arrive quickly, bringing with them a lot of thunder, lightning, and heavy rain. Monsoon burst is the name given to this sudden onset of rain.
• Monsoons can be delayed or arrive much earlier than expected.
• The onset usually occurs between the 29th of May and the 7th of June.
• The earliest onset dates were May 11th, 1918, and May 11th, 1955, respectively, while the most delayed onset date was June 18th, 1972.

South West Monsoon Rainfall