How does a cyclone affect the monsoon’s onset?

Context
The cyclone ‘Biparjoy’ formed in Arabian Sea is declared as ‘very severe cyclone’, and climatologists suggest that it can affect onset of Monsoon in India.
  • As the effect of Global warming, the occurrence of cyclones in Indian Ocean and typhoons in North-western Pacific Ocean is changing, which has a significant impact on onset and withdrawal of monsoon in India.
Changing scenario:
  • Against the conventional pattern of occurrence of cyclones usually post-monsoon (October-November) has shifted to pre-monsoon times (April-May).
  • This unusual occurrence of cyclones either in Arabian Sea or Bay of Bengal affects the monsoon showers over Indian subcontinent.
  • As we know that, the course of monsoon usually is affected by the three tropical oceans – Indian, Atlantic, and Pacific.
About Monsoon:
  • The “monsoon” climate is related to the seasonal reversal of wind direction.
  • The monsoons are a seasonal wind pattern that travels from the sea to the land in the summer and from the sea to the land in the winter.
  • The Indian subcontinent, central-western Africa, Southeast Asia, and a few other regions all have monsoons, but the winds are highest in the Indian subcontinent.
Onset of the Monsoon:
  • In April and May, when the sun shines vertically over the Tropic of Cancer, the huge continent to the north of the Indian Ocean gets exceedingly hot.
  • This causes an intense low-pressure system to build in the north western section of the subcontinent.
  • Because the pressure in the Indian Ocean to the south of the landmass is high due to the slow heating of water, the low-pressure cell attracts southeast trades over the Equator.
  • These factors help the ITCZ to move northward.
  • The southwest monsoon can be considered as a continuation of the southeast trades deflected towards the Indian subcontinent after crossing the Equator.
  • These winds cross the Equator between 40°E and 60°E longitudes.
  • The southwest monsoon arrives on the Kerala coast on June 1st and sweeps fast through Mumbai and Kolkata from June 10th to June 13th.
  • By mid-July, the southwest monsoon has engulfed the whole subcontinent.
How position of cyclone affects Monsoonal winds?
  • For Cyclones in North Indian Ocean:
    • Since the circulation of winds around the cyclones is in the anticlockwise direction, the location of the cyclone is critical as far as the cyclone’s impact on the transition of the monsoon trough is concerned.
    • The monsoon trough is a low-pressure region that is a characteristic feature of the monsoons.
    • For example, if a cyclone lies further north in the Bay of Bengal, the back-winds blowing from the southwest to the northeast can pull the monsoon trough forward, and assist in the monsoon’s onset.
  • South-westerly winds over the Arabian Sea are positive for onset as they bring large quantities of moisture onto the Indian subcontinent.
  • On the other hand, south-westerly winds over the Bay of Bengal are bad news for the monsoon.
Monsoon Trough:
  • A trough is a belt of low pressure extending to large area. This trough seen during monsoon period, hence known as Monsoon trough.
  • Monsoon trough is a part of the Inter Tropical Convergence Zone (ITCZ) where the northern hemisphere and southern hemisphere winds meet.
  • This is normally shown as a line connecting the location of monsoon low pressure areas.
  • These troughs run across continents during peak monsoon periods.
 Impacts of early or delays in Monsoon:
  • On Agriculture:
    • The early arrival of monsoon rains in central and northern India will help farmers accelerate sowing of summer-sown crops such as paddy rice, cotton, soybean and pulses, and may boost crop yields too.
    • The early arrival of monsoon rains in central and northern India will help farmers accelerate sowing of summer-sown crops such as paddy rice, cotton, soybean and pulses, and may boost crop yields too.
  • On Climate:
    • These variations are generally considered normal, given the complexity of the monsoon.
    • However, climate experts have linked extreme weather events like intense rainfall over a region within a short time span or prolonged dry spell during the four months (June-September) as indications of climate change.
  • On Economy:
    • A healthy monsoon season increases farm productivity, which raises rural households’ income and the demand for consumer items.
    • Poor monsoon conditions, on the other hand, reduce demand for rural homes, tractors, and FMCG goods. Additionally, it pushes the government to spend money on food imports and implement policies like waiving farm loan payments.

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