SEASONS IN INDIA
There are three seasons in India: summer, winter and monsoon. The climate of India is essentially sub-tropical monsoonic. The word ‘monsoon’ has been derived from the Arabic word “Mausim” which means ‘season’. Originally, the word ‘monsoon’ was, used by Arab navigators several centuries ago, to describe a system of seasonal reversal of winds along the shores of the Indian Ocean, especially over the Arabian Sea, in which the winds blow from the south-west to north-east during the summer season and from the north-east to south-west during the winter season.
Monsoon is a unique weather phenomenon due to seasonal reversal of winds.
Monsoon has following features:
INDIAN MONSOON
Stage 1:
The apparent movement of the sun in northern hemisphere in summer is seen. This heats the Tibetan plateau and the air rises upwards. This creates a Tropical Eastern Jetstream which descends at Madagascar and creates a high pressure zone there. An inter tropical convergence zone [ITCZ] formed at equator moves to Tibetan plateau.
Fig 1: Indian monsoon
Stage 2:
The Somali jet stream intensifies the Somalian ocean current during summer. Stronger the Somalian current better the monsoon.
Stage 3:
Sub tropical westerly jet maintains high pressure over North India. The STWJ is bifurcated by the Himalayas into two branches.
Fig 2: STWJ and Himalayas
The summer see apparent movement of the sun and heating of the Tibetan plateau. This creates a low pressure belt over Tibet.
The STWJ still continues to be over South Himalayas and it resists the monsoon winds.
In this time there is local convectional rainfall in Bengal, Bihar called Kalbaisakhi , mango showers. These are pre monsoon thunder showers.
Then the STWJ southern branch moves over north and STWJ withdraws from the Indian subcontinent. If this branch reestablishes then monsoon break is seen.
Stage 4: Indian Ocean Dipole
Low pressure conditions over Australia and Tibetan plateau and high pressure over Madagascar create an Indian ocean dipole. A strong dipole pushes monsoon winds towards Indian subcontinent.
Fig 3: Indian Ocean Dipole
Stage 5: onset of monsoon
The monsoon winds have two branches Arabian and Bay of Bengal. The Arabian branch moves over western ghats and is blocked. This brings heavy rainfall over western region.
The SW Arabian branch isn’t blocked by Aravallis so less monsoon over Rajasthan. The gap between Vindhyas and Aravallis mean SW winds reach over to Himachal Pradesh.
The Eastern branch of the SW monsoon goes over Bay of Bengal and isn’t blocked by the eastern ghats. It passes through their gaps and reaches Vindhya , Satpuda range and Chota Nagpur plateau. This gives rainfall to the Eastern India and interiors.
The second part of the eastern branch of sw monsoon passes over north east and brings rain there.
Stage 6: retreat monsoon
The month of September the ITCZ retreats towards the equator from Tibetan plateau. As it passes over the India the eastern branch of South west monsoon and north east winds collide.
The eastern branch of South west monsoon withdraws first. Then North East winds are off land and hence dry but they pick moisture over Bay of Bengal and bring rain to southern tip of India i.e. Coast of Andhra Pradesh, Tamil Nadu.
The retreating eastern branch of South west monsoon brings cyclones to the land.
Fig 4: Indian Monsoon
Q.With reference to ‘Indian Ocean Dipole (IOD)’ sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct?
1. IOD phenomenon is characterized by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
2. An IOD phenomenon can influence an El Nino’s impact on the monsoon. Select the correct answer using the code given below: (UPSC CSAT 2017)
Ans . B
Q.Consider the following statements:
1. In India, the Himalayas are spread over five States only.
2. Western Ghats are spread over five States only.
3. Pulicat Lake is spread over two States only.
Which of the statements given above is/are correct? (UPSC CSAT 2017)
Ans . B
Q.With reference to river Teesta, consider the following statements:
1. The source of river Teesta is the same as that of Brahmaputra but it flows through Sikkim.
2. River Rangeet originates in Sikkim and it is a tributary of river Teesta.
3. River Teesta flows into Bay of Bengal on the border of India and Bangladesh.
Which of the statements given above is/are correct? (UPSC CSAT 2017)
Ans . B
Q.If you travel by road from Kohima to Kottayam, what is the minimum number of States within India through which you can travel, including the origin and the destination? (UPSC CSAT 2017)
Ans . B
Q.At one of the places in India, if you stand on the seashore and watch the sea, you will find that the sea water recedes from the shore line a few kilometres and comes back to the shore, twice a day, and you can actually walk on the sea floor when the water recedes. This unique phenomenon is seen at (UPSC CSAT 2017)
Ans . C
Q.Which of the following is geographically closest to Great Nicobar ? (UPSC CSAT 2017)
Ans . A
Q.Mediterranean Sea is a border of which of the following countries?
Jordan
Iraq
Lebanon
Syria
Select the correct answer using the code given below: (UPSC CSAT 2017)
Ans . C
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Q1:Indian Monsoon is a unique weather phenomenon due to
Q2: The low pressure zone due to intense heating is known as
Q3:Fluctuations in Indian monsoon may be due to
Q4: Cyclones make landfall in South eastern India due to
Q5:Which would contribute to high rainfall in India