Marine heatwave fuelled super cyclone Amphan

Marine heatwave fuelled super cyclone Amphan

Subject :Geography

Section: Climatology

Context:

• A study, published in the Frontiers in Climate, is the first study conducted in the Indian Ocean that investigates the interaction between a marine heatwave and super cyclone Amphan in the Bay of Bengal in May 2020. 

Marine heatwaves

• The high sea surface temperatures are more susceptible to generating extreme temperature conditions that persist over days to months and are termed as Marine Heat- waves (MHWs).
• Previous studies have shown that due to global warming,the tropical Indian Ocean, at the surface, is warming at a faster rate as compared to the rest of the global ocean.

Relation between Marine heatwaves and tropical cyclones:

• The anthropogenic warming of the oceans and atmosphere facilitates the generation and intensification of extreme events such as MHWs and tropical cyclones.
• The intense warming of the ocean due to MHW has severe socio-economic consequences such as fish mortality, and coral bleaching, and also has the potential to interact and modify other extreme events such as tropical cyclones.
• Both marine heat waves and tropical cyclones are the extreme events of the ocean-atmosphere coupled system.
• The co-occurrence of multiple extreme events (e.g.in our case the co-occurring marine heatwave and tropical cyclone) are termed compound extreme events.

Sea surface temperature in Bay of Bengal:

• The Bay of Bengal exhibits high sea surface temperatures (about 28°C) through-out the year and is more prone to tropical cyclones.
• The Bay of Bengal is home to about 5-7% of the total number of tropical cyclones occurring globally each year and this makes the North Indian Ocean vulnerable to the highest number of fatalities globally.
• Amphan was the first super cyclone in the Bay of Bengal in the last 21 years and intensified from category 1 (cyclonic storm) to category 5 (super cyclone) in less than 24 hours. 

Factors responsible of Super Cyclone Amphan

• It was found the presence of a strong MHW beneath the track of the cyclone with an extremely high anomalous sea surface temperature of more than 2.5°C that coincided with the cyclone track and facilitated its rapid intensification in a short period.
• The study has compared the super cyclone Amphan to a previous extremely severe cyclone Fani in May 2019 with a near similar trajectory.
• The total life span of Amphan over the ocean was five days as com- pared to Fani which was for seven days but Fani did not turn into a super cyclone as Amphan did.
• The main difference between these two cyclones was the presence of MHW in the case of Amphan, which was not there in the case of Fani. 
• The study also inferred that despite short duration and unfavourable atmospheric conditions relative to Fani, Amphan turned into a super cyclone, primarily fuelled by a strong MHW on its way. 
• Apart from the surface warming, the study also shows that ocean stratification and warming below the surface also play a crucial role during this phenomenon of compound extreme events.