El Niño, the warming of sea surface temperatures in the central and eastern Pacific Ocean associated with the positive phase of the El Niño Southern Oscillation (ENSO), is already known to influence India’s monsoon. A new study now suggests that ENSO may also play a significant role in determining the number of tropical cyclones that form in the Bay of Bengal during the post-monsoon season (October to December).

Scientists from the Hyderabad-based Indian National Centre for Ocean Information Services (INCOIS) found that cyclone activity in the Bay of Bengal varies considerably depending on whether El Niño, La Niña, or neutral ENSO conditions prevail.

La Niña, the negative phase of ENSO, is characterised by unusually cool sea surface temperatures in the central and eastern Pacific Ocean. During La Niña years, the tropical Indian Ocean generally remains relatively cooler, influencing large-scale ocean-atmosphere interactions that can affect cyclone formation.

The study, conducted by P. Suneeta, T.V.S. Udaya Bhaskar and S.S.V.S. Ramakrishna, analysed cyclone activity between 1995 and 2019. The researchers found that only 15 cyclones formed during nine El Niño years. In contrast, cyclone activity more than doubled during 11 La Niña years, with 33 cyclones recorded. Neutral years also witnessed relatively high activity, with 17 cyclones forming over five years.

Tropical cyclones are among the most destructive weather systems affecting countries around the Bay of Bengal, often causing widespread damage through strong winds, heavy rainfall and storm surges. Forecasting cyclone formation remains challenging because it depends on a complex interaction of atmospheric and oceanic conditions, said scientists.

To better understand these factors, the researchers examined the Genesis Potential Index (GPI), a measure used to assess how favourable environmental conditions are for cyclone formation. The study revealed significant differences in GPI values across ENSO phases.

La Niña years provided a more conducive environment for cyclone development due to lower vertical wind shear, warmer sea surface temperatures in the region and stronger air-sea interactions. Hence, GPI values during La Niña conditions were found to be nearly twice as high as those recorded during El Niño and neutral years.

The study highlights the strong influence of ENSO-driven oceanic and atmospheric changes on cyclone activity in the Bay of Bengal. The researchers believe that incorporating these large-scale climate patterns into forecasting models could improve cyclone prediction and strengthen disaster preparedness efforts.

While the findings indicate a clear association between La Niña events and increased cyclone activity, the authors emphasised that further research using longer data records is needed to better understand the mechanisms governing cyclone formation in the region. The research was carried out y INCOIS under the Ministry of Earth Sciences in collaboration with Andhra University, Visakhapatnam.