Monsoon / Monsoon in India.

MONSOON 

Monsoon meaning, a major wind system that seasonally reverses its direction—such as one that blows for approximately six months from the northeast and six months from the southwest. The most prominent monsoons occur in south asia, Africa, Austrilia, and the Pacific coast of central America, Monsoonal tendencies also are apparent along the gulf coast of the United States and in central Europe; however, true monsoons do not occur in those regions.

Monsoon in India (diagram1)

Monsoons are seasonal winds [periodic  winds ] which reverse their direction with the change of season.

The Monsoon is a double system of seasonal winds - they flow from sea to land during the summer and from land to sea during winter .

Some scholars tends to treat the monsoon winds as land and sea  breeze on a large scale .

monsoons are peciluar to indian subcontinent , south east asia parts of central  western africa ,etc 

They are more pronounced in the Indian subcontinent compared to any other region .

Indian monsoon are convection cells on an immense scale.

India recieves South westmonsoon winds in summer and north east monsoon winds in winter.

Factors influencing intensity of SW monsoons:

1. Strengths of the low pressure over Tibetan plateau and the high pressure over the south Indian Ocean
2. Somali Jet
3. Somali Current
4. Indian Ocean dipole
5. Indian Ocean branch of the Walker Cell

What are the two branches of Southwest Monsoon?

The southwest monsoon arrives in two branches called the Bay of Bengal branch and the Arabian Sea branch. The Arabian Sea side monsoon creates a low-pressure area on the Thar Desert. It is quite stronger than the Bay of Bengal side monsoon.

Which Indian state is the first to receive the Southwest Monsoon rains?

The Arabian Sea Branch of the Southwest Monsoon first hits the Western Ghats of the coastal state of Kerala, India, thus making this area the first state in India to receive rain from the Southwest Monsoon.

Why does the Southwest monsoon break into two branches?

South West monsoon winds break into two branches due to topographic factors. When the South West Monsoon wind hits the Western Ghats it branches into two parts, the Arabian Sea branch and the Bay of Bengal Branch.

Why does the Tamil Nadu coast remain dry during Southwest Monsoon?

During the South-West Monsoon, Tamil Nadu remains dry because it is located in a rain shadow area. Tamil Nadu has rain during the monsoon season due to the southwest trade winds which blow towards the northern hemisphere. Tamil Nadu receives rainfall in the winter season due to northeast trade winds.

Why does the Southwest Monsoon bring heavy rains?

Summer Monsoon weather is characterized by a strong, generally West or southwest breeze that is responsible for bringing significant rainfall to the Asian subcontinent and to South and East Asia. The significant southwest monsoon rainfall is a by-product of air passing over large areas of warm equatorial ocean, stimulating increased levels of evaporation from the ocean’s surface; the southwest monsoon air, now laden with water vapour, cools as it moves north and as it rises over land; at some point the air is no longer able retain its moisture and precipitates copious volumes to irrigate rice fields and drench rainforests, sometimes causing severe flooding.

Northeast Monsoon:

Cause: High-pressure cells over the Tibetan and the Siberian Plateaus

NE monsoon winds bring rainfall to the southeast coast of the country (Tamil Nadu coast and Seemandhra’s south coast).

Factors responsible for the formation of the NE Monsoons:

1. Formation and strengths of the high-pressure cells over the Tibetan and the Siberian Plateaus during winters
2. Migration of the Inter-Tropical Convergence Zone (ITCZ) to the south of India
3. The high-pressure cells in the southern Indian Ocean migrating to the west and weakening

[Inter Tropical Convergence Zone:-The Inter Tropical Convergence Zone (ITCZ,) is a broad trough of low pressure in equatorial latitudes. This is where the northeast and the southeast trade winds converge. This convergence zone lies more or less parallel to the equator but moves north or south with the apparent movement of the sun]

Mechanism of Indian Monsoon:

1. Theories of origin of monsoon ( onset of indian monsoon)

  origin of monsoon is still a mystery and reseach is still going on in that perspective . Therre are four main theories of the origin of monsoon ;

A). Thermal theory of Halley (diagram 2)

 it was based on the concept of differential heating of land and ocean .

During summer , the land is heated more intensively, leading to a low pressure on indian landmass . At the same time , the ocean is relatively less warmer and has more pressure . So this pressure difference induces on shore winds from the ocean whioch are moisture laden.

However , this theory did not expklain- 

   Why does monsoon start in the first week of june ?

    Why were there breaks in the monsoons?

B). Equatorial westerly theory of flohn(diagram 3)

   It was also based on thermal origin , but here southwest monsoon is moidified planetary winds in the inter - tropical convergent zone [ITCZ]

   During summer , itcz will be in north hemisphere because of apparent northward movement of sun.

   During winter , itcz will be south of the equator so there will be reversal of wind system as shown in the diagram (3) .

This is known as northeast monsoon which brings rainfall to coromandel coast. 

  This theory also could  not explain questions which were unanswered in Thermal theory.

 

C). Jet sream theory by M.T.Yin and Koteshwaram

     The jet sream is very fast blowing air current system in the upper atmosphere . This system works as a cover for the earth and affects the weather of the lower atmosphere . This theory is now accepted as the most scientific explanation  of Indian monsoon.

Impact of Monsoons on Life in India

Positive

• About 64% of people in India depend on agriculture for their livelihood and agriculture itself is based on monsoon.
• Agricultural prosperity of India depends very much on timely and adequately distributed rainfall. If it fails, agriculture is adversely affected particularly in those regions where means of irrigation are not developed.
• Regional variations in monsoon climate help in growing various types of crops.
• Regional monsoon variation in India is reflected in the vast variety of food, clothes and house types.
• Monsoon rain helps recharge dams and reservoirs, which is further used for the generation of hydro-electric power.
• Winter rainfall by temperate cyclones in north India is highly beneficial for Rabi crops.

Negative

• Variability of rainfall brings droughts or floods every year in some parts of the country.
• Sudden monsoon burst creates a problem of soil erosion over large areas in India.
• In hilly areas sudden rainfall brings landslide which damages natural and physical infrastructure subsequently disrupting human life economically as well as socially.