What are the monsoon characteristics of India? And why is the onset of southwest monsoon over Kerala delayed for a few days?
What is Indian Monsoon?
Monsoons are the seasonal return of winds that bring moisture-laden winds to the Indian subcontinent and cause rainfall.
It can also be described as seasonal changes in atmospheric circulation and precipitation due to annual latitudinal fluctuations of the Intertropical Convergence Zone (ITCZ) between north and south of the equator.
Indian monsoon features:
Dry spells and wet spells: Monsoon in India clearly has a wet phase and a dry phase, characterized by weeks in which there is no rainfall.
Uneven distribution: Monsoons are unevenly distributed and the peninsular part of India receives more rainfall than the plains.
Influence of Topography: Monsoons are influenced by topography. The western part of the Western Ghats receives heavy rainfall while the eastern side is deficient.
Fixed schedule: Monsoons in India usually have a fixed schedule. It usually starts in the first week of June and ends by September.
How does a monsoon work?
Importance of monsoon
Source of Water: Monsoons account for approximately 80% of India's rainfall. It is in charge of supplying the country's exhausted water resources.
Irrigation: Majority of India depends on monsoon rains to irrigate its crops. This makes it vital for India's food security.
Economy: India is predominantly an agrarian economy with the majority depending on agriculture for livelihood. Monsoon delays can disrupt economic growth and can have a domino effect.
Sustained flora and fauna: India's vast biodiversity is supported by the rains of the monsoon season. Monsoons are responsible for maintaining the ecological balance.
Monsoon mechanism
During summer, the northward shift of the ITCZ helps create a low pressure area over Asia as well as north and northwest India.
A high pressure system develops over the southern Indian Ocean at the same time.
The low pressure system over the land of India attracts the south-easterly trade winds of the Southern Hemisphere, resulting in a rightward rotation of the Coriolis force towards the low pressure areas over the Indian subcontinent.
These south-westerly winds enter peninsular India as south-west monsoons. Since they blow over warm oceans, they bring a lot of moisture to the subcontinent.
After 100-120 days, the low pressure system over north and northwest India weakens due to southward shift of ITCZ. This leads to the withdrawal of monsoons.
Conditions affecting the monsoon
Mascarene high: The presence of this high pressure area near Madagascar helps to disperse moisture-laden winds towards the Indian subcontinent.
Low pressure in the Tibetan Plateau: During the summer, the Tibetan Plateau heats up greatly, resulting in a low pressure area that attracts the trade winds.
Northward shift of the Intertropical Convergence Zone (ITCZ): The northward shift of the ITCZ over north and northwest India creates a low pressure area called the monsoon trough.
Differential cooling of land and sea: Differential cooling creates a low pressure over the land of India while the surrounding seas experience relatively high pressure.
Western jet stream shift: This shift to the north of the Himalayas creates the necessary temperature for monsoons to enter.
Southern Oscillation: El Nino or La Nina conditions strengthen or weaken the Indian monsoon depending on the occurrence.
Monsoon characteristics of India
The onset and progression of monsoons
The onset of the monsoon over Kerala marks the beginning of the four-month southwest monsoon season (June–September), which is responsible for supplying 70% of India's annual rainfall.
However, the start does not mean the first rain of the season. The first rains start even before the start is announced in certain places.
Delay or early onset of monsoon does not affect the quality or amount of rainfall or its regional distribution across the country.
The onset of the monsoon occurs when there is a significant change in the large-scale atmospheric and oceanic circulations in the Indo-Pacific region.
Before the IMD declares the onset of monsoon in India, certain conditions must be met:
rainfall intensity
The start is declared when at least 60 percent of the 14 designated weather stations in Kerala and Lakshadweep record at least 2.5 mm of rain for two consecutive days after May 10.
These stations include Amini, Minikoi, Thiruvananthapuram, Punalur, Kollam, Alappuzha, Kochi, Kottayam, Thrissur, Kozhikode, Thalassery, Kannur, Kasaragod and Mangalore.
The start in Kerala will be announced on the second day, if certain wind and temperature criteria are also met.
wind conditions
Westerlies should be as deep as 600 hPa in the area bounded by the equator at latitude 10°N and from longitude 55°E to 80°E.
The zonal wind speed over the area limited to latitude 5-10°N (Maldives to Kochi) and longitude 70-80°E (Arabian Sea to Chennai) should be of the order of 15-20 knots at 925 hPa.
heat
The amount of outgoing longwave radiation (OLR), which is the combined value of energy emitted into space from the land surface, oceans and atmosphere, should be less than 200 W/m2 in the area between latitudes 5°N and 10°N and 70°E and be eastern Longitude 75 degrees east... Read more at: https://www.studyiq.com/articles/characteristics-of-indian-monsoon/#
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