The tropical supercyclone Amphan recently made news as it is predicted to landfall between the Sagar islands of West Bengal and the Hatiya islands of Bangladesh. This storm, born over the Bay of Bengal, has intensified into a super cyclonic storm with a maximum wind speed of 120 knots. Notably, this is the strongest storm to arise in the Bay of Bengal since a similar storm devastated Paradip in Odisha, back in 1999.
The Making of a Supercyclone
Amphan rose to power due to some unique environmental factors including higher than usual temperatures in the Bay of Bengal (BoB). Cyclones gather their energy from the heat and moisture emitted from warm ocean surfaces. BoB typically carries higher Sea Surface Temperature (SST) in comparison with the Arabian Sea, making it a conducive environment for cyclone formation. Some of the contributing factors to the high SST in the Bay of Bengal include slow-moving winds, increased rainfall, and constant influx of freshwater from the Ganga and Brahmaputra rivers.
Contribution of Global Warming
The summer of 2020 saw a significant rise in temperatures in the BoB, attached to global warming driven by fossil fuel emissions. High temperatures were also a key factor in fuelling the cyclone Fani in 2019. The first two weeks in May observed surface temperatures peaking at 32-34°C continuously, marking the highest recorded temperatures to date.
Impact of COVID-19 Lockdown
Ironically, the countrywide lockdown due to the COVID-19 pandemic indirectly influenced the creation of this super cyclone. The lockdown led to decreased particulate matter emissions, resulting in fewer sunlight reflecting aerosols such as black carbon. Every year, pollution from the Indo-Gangetic plains transports particulate matter to the BoB, forming clouds that cover the ocean. With fewer aerosols present due to the lockdown, there were fewer clouds formed and more heat accumulated, leading to a temperature rise between 1-3°C higher than normal.
The Quick Evolution of Amphan
The combination of high temperatures and minimal aerosols allowed the cyclone Amphan to rapidly strengthen from a category-1 cyclone to a category-5 in just 18 hours; an unusually quick evolution.
About Cyclones
Cyclones are systems characterized by a very low-pressure center and high-speed winds that revolve around it. Various elements including wind speed and direction, temperature, and humidity play a role in cyclone development. Hurricanes utilize energy from heated seawater and their strength can be disrupted by the presence of upper-level-winds that disrupt storm circulation.
