How does a cyclone affect the monsoon’s onset?


  • The impact of global warming on the monsoons are manifest in the onset, withdrawal, its seasonal total rainfall, and its extremes.

  • Global warming also affects the cyclones over the Indian Ocean and the typhoons over the northwestern Pacific Ocean.

Key Details

  • We’re seeing cyclone formations in the pre-monsoon cyclone season, closer to the monsoon onset, arguably due to the influence of a warmer Arctic Ocean on winds over the Arabian Sea. A snapshot of winds over the Arabian Sea and the Bay of Bengal at 3.15 pm on June 8, 2023.

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  • The monsoon is of course also affected by the three tropical oceans – Indian, Atlantic, and Pacific; the ‘atmospheric bridge’ from the Arctic; and the oceanic tunnel as well as the atmospheric bridge from the Southern Ocean (a.k.a. the Antarctic Ocean).
  • A ‘bridge’ refers to two faraway regions interacting in the atmosphere while a ‘tunnel’ refers to two remote oceanic regions connecting within the ocean.

Why does a cyclone’s position matter?

  • Some cyclones in the North Indian Ocean have had both positive and negative impacts on the onset of the monsoon.
  • 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.
  • Earlier this year, the Bay of Bengal had Cyclone Mocha develop in the first half of May and intensify briefly into a ‘super cyclonic storm’, before weakening rapidly upon landfall.
  • The late-season cyclone Biparjoy is still chugging along in the warm Arabian Sea and may well rapidly intensify – i.e., have its wind speeds increase by 55 kmph within 24 hours – before making landfall.
  • Mawar qualified as a ‘super typhoon’ and is thus far the strongest typhoon to have taken shape in May. It is also the strongest cyclone of 2023 so far.
  • Tropical storm Guchol is now active just to the east of the Philippines and is likely to continue northwest before veering off to the northeast.
  • Southwesterly winds over the Arabian Sea are welcome news: they bring large quantities of moisture onto the Indian subcontinent. On the other hand, southwesterly winds over the Bay of Bengal are bad news for the monsoon. 

Source: TH

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