Cyclone’s effect on monsoon onset

Source: The post is based on the article “Cyclone’s effect on monsoon onset” published in The Hindu on 9th June 2023

What is the News?

Cyclone formations in the pre-monsoon cyclone season, closer to the monsoon onset, may be due to the influence of a warmer Arctic Ocean on the winds over the Arabian Sea.

What are the factors which affect the Monsoons?

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

The monsoon is 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 (Antarctic Ocean).

Note: A ‘bridge’ refers to two faraway regions interacting in the atmosphere while a ‘tunnel’ refers to two remote oceanic regions connecting within the ocean.

How Monsoon and cyclone patterns are shifting?

Monsoon: The conventional pattern of occurrence of cyclones usually post-monsoon (October-November) has shifted to pre-monsoon times (April-May).

Cyclone: There is an unusual occurrence of cyclones either in the Arabian Sea or the Bay of Bengal affects the monsoon over the Indian subcontinent. Some cyclones in the North Indian Ocean have had both positive and negative impacts on the onset of the monsoon.

Interaction between cyclone and monsoon: Both the Arabian Sea and the Bay of Bengal have warmed by more than 1º C in the pre-monsoon season. Further, the location of the cyclone is critical on the monsoon trough as the circulation of winds around the cyclones is in the anticlockwise direction.

Note: The monsoon trough is a low-pressure region that is a characteristic feature of the monsoons.

What is the recent Cyclone’s effect on monsoon?

Cyclone Mocha: It was developed in the Bay of Bengal in the first half of May. It intensified into a ‘super cyclonic storm’. Mocha’s northwest-to-east trajectory over the Bay was the result of the presence of unusual anticyclones (which rotate clockwise) over the Arabian Sea and the Bay of Bengal since March.

Cyclone Biparjoy: It was formed in the Arabian Sea. Its late birth and the late onset of the monsoon are both closely related to typhoons in the northwestern Pacific Ocean. So, Biparjoy may rapidly intensify before making landfall.

Typhoon Mawar: It is 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: It is now active just to the east of the Philippines and is likely to continue northwest before veering off to the northeast.

Both Mawar and Guchol have contributed to the Southwesterly winds that hinder the progress of the monsoon trough.

How cyclone’s effect on monsoon has impacted the prediction of the onset of monsoon?

The monsoon trough, once considered a reliable system, is now subject to the uncertainties of climate change. So, now the monsoons are now like small cars moving along the strong South-Westerly winds over the Bay of Bengal which act like highways.

The intricate interplay between global warming, cyclogenesis, and typhoon activity in the Pacific and North Indian Oceans presents challenges in accurately predicting the monsoon onset and its evolution.

However, a late monsoon onset does not necessarily indicate a deficit in rainfall.