Warmer subsurface waters in Bay of Bengal

Warmer subsurface waters in Bay of Bengal

Subject: Geography

Section: Physical geography

Context:

• Warm subsurface waters in the Bay of Bengal likely helped fuel the 2020 Amphan super cyclone, a new study has suggested.
• This shows a link between marine heatwaves and cyclones.

Impacts of Warm subsurface waters:

• Warmer surface waters may have also helped sustain marine heatwaves — prolonged high sea temperatures.
• Marine heatwaves also likely helped intensify the cyclone from Category 1 (cyclonic storm) to Category 5 (super cyclone) in less than 36 hours, the study published in Frontiers in Climate, reported.
• Amphan was the first super cyclone in the Bay of Bengal in the last 21 years. It was also the costliest tropical cyclone on record in the North Indian Ocean.

Link between marine heatwaves and cyclones.

• Cyclones are an extreme event, and so are marine heat events.
• Researchers from France, Australia and India investigated the events that led to the formation of the Amphan super cyclone.
• The sea surface temperature in the southern and northern portions of the Ocean was close to 1.5 and 2°C above the average of 30.2 and 29.7°C, respectively, the study noted.
• A strong marine heatwave covered close to 300,000 square kilometres of the basin.
• Warm subsurface waters could intensify cyclones by allowing heat to flow between the sea and atmosphere. Warmer waters fuel cyclones
• The sea temperatures cooled as the cyclone approached the coast. Subsurface warming also went down, bringing the marine heatwave event to a close.
• Future studies can evaluate how the atmosphere helps marine heatwave fuels cyclones.

What are Tropical Cyclones ?

• Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction due to violent winds, very heavy rainfall and storm surge.
• They are irregular wind movements involving closed circulation of air around a low pressure center. This closed air circulation is a result of rapid upward movement of hot air which is subjected to Coriolis force.

Conditions Favourable for Tropical Cyclone Formation

• Large sea surface with temperature higher than 27°C.
• Presence of the Coriolis force, enough to create a cyclonic vortex.
• Small variations in the vertical wind speed.
• A pre-existing weak low-pressure area or low-level-cyclonic circulation.
• Upper divergence above the sea level system.