Cyclone’s effect on monsoon onset

General Studies Paper 1

Context-

• Global warming’s effects on cyclogenesis over the Pacific and North Indian Oceans, the warming over the North Indian Ocean and the late pre-monsoon cyclones and typhoons are another monkey wrench in the monsoons’ dynamics – and in the predictions of the monsoon’s onset and its evolution through the season.

The impact

• We are 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 the winds over the Arabian Sea.
• 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.

Importance of a cyclone’s position

• 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.
• 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 as evident with Cyclone Mocha which developed in the first half of May and intensify briefly into a ‘super cyclonic storm.
• One severe consequence of the anomalous anticyclones since March is that both the Arabian Sea and the Bay of Bengal have warmed by more than 1º C in the pre-monsoon season.

Mawar, Biparjoy, and Guchol

• Cyclone Biparjoy is not interacting much with the monsoon trough at this time. However, its late birth as well as the late onset of the monsoon are both closely related to typhoons in the northwestern Pacific Ocean.
• On May 19, Typhoon Mawar was born and dissipated by June 3. 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. These powerful typhoons are thirsty beasts and demand moisture from far and wide.

 Southwesterly winds

• Cyclone Mawar pulled winds across the equator into the North Indian Ocean, setting up south-westerly winds over parts of the Arabian Sea and the Bay of Bengal.
• Southwesterly’ means blowing from the southwest.
• 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.
• The monsoon winds over the southern Bay of Bengal sweep in from the southwest and west, but they turn around and head northwest towards India from the southeast.

Conclusion

• This complicated dance of global warming affecting cyclogenesis over the Pacific and North Indian Oceans, the warming over the North Indian Ocean and the late pre-monsoon cyclones and typhoons together is just another monkey wrench in the monsoons’ dynamics — and in the predictions of the monsoon’s onset and its evolution through the season. Once seen as a very reliable system, with its annual migration north-westward and the withdrawal south-eastward, the monsoon trough is now being kicked around in the game of climate-change football.