How marine heatwave fuelled super cyclone Amphan

Context

A new study has suggested that warm subsurface waters in the Bay of Bengal likely helped fuel the 2020 Amphan super cyclone.

About

Marine heatwaves:

First described in 2011: The term “marine heatwave” was initially used to describe an extreme surface warming event off the west coast of Australia during 2010-11 austral summer.
Marine heatwaves like The Blob has resulted in mass mortalities in marine mammals and birds, and collapse of fisheries and aquaculture in the US, Korea, etc.
Marine heatwaves are periods of extremely high temperatures in the ocean (above the 90th percentile).
These events cause marine habitat destruction due to coral bleaching, seagrass destruction, and loss of kelp forests, affecting the fisheries sector adversely.
Impact on the Monsoon
The marine heatwaves in the western Indian Ocean and the Bay of Bengal are found to result in dry conditions over the central Indian subcontinent.
There is an increase in rainfall over south peninsular India in response to the heatwaves in the Bay.

What causes marine heatwaves?

Marine heatwaves can be caused by a whole range of factors, and not all factors are important for each event.
The most common drivers of marine heatwaves include ocean currents which can build up areas of warm water and air-sea heat flux, or warming through the ocean surface from the atmosphere.
Winds can enhance or suppress the warming in a marine heatwave, and climate models like El Niño can change the likelihood of events occurring in certain regions.

Trends:

Bay of Bengal recorded surface temperatures of 32-34°C, before Cyclone Amphan.
93% of the heat from global warming goes into the oceans.
Warm waters are an energy source for cyclones.
As the Arabian Sea warms, the number and intensity of cyclones and heavy rains increase.
Over the Arabian Sea,
150% rise in the number of very severe cyclones
80% rise in the total duration of cyclones
20%-40% rise in the intensity of cyclones Over the Bay of Bengal, rapid intensification may be occurring more.

Key findings about Marine heatwave and Cyclone:

The heat content in the subsurface ranged between 135 and 150 kilojoules per square centimetre before the cyclone.
Warm subsurface waters could intensify cyclones by allowing heat to flow between the sea and atmosphere. Warmer waters fuel cyclones.
The subsurface water may have warmed because of the high sea level anomaly, which is the difference between the total and average sea level.
An increase in sea level is brought about by anticyclonic eddies, which is a circular movement of water.