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Rise in frequency and intensity of cyclones in Arabian Sea

GS Paper 1

Topics Covered: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc.

 

Context:

The frequency and intensity of cyclones developing over the Arabian Sea has increased in the last two decades, while fewer such storms have been seen over the Bay of Bengal.

 

Key changes:

  • A 52% increase was noticed in the frequency of cyclones over the Arabian Sea between 2001 and 2019 , and an 8% decrease over the Bay of Bengal.
  • The number of very severe cyclones in the Arabian Sea has gone up by 150% during the last two decades.

 

Factors responsible for this:

  1. Surface temperatures in the Arabian Sea have increased rapidly during the past century due to global warming. Temp. Now is 1.2–1.4 °C higher than the temperature witnessed four decades ago. These warmer temperatures support active convection, heavy rainfall, and intense cyclones.
  2. The rising temperature is also enabling the Arabian Sea to supply ample energy for the intensification of cyclones.
  3. The Arabian Sea is also providing conducive wind shear for cyclones. For instance, a higher level easterly wind drove the depression of Cyclone Ockhi from the Bay of Bengal to the Arabian Sea.

 

Concerns:

This underlines the increasing risk of disasters hitting the west coast of India if the trend continues to hold over the years.

 

How are cyclones formed?

Cyclones are formed over the oceanic water in the tropical region. In this region, the sunlight is highest which results in warming of land and water surface. Due to warming of the surface, the warm moist air over the ocean rises upwards following which cool air rushes in to fill the void, they too get warm and rise — the cycle continues.

 

But what creates the spin?

Wind always blows from high pressure to low pressure areas. High pressure areas are created in the cold region while low is created in the warm regions. Polar regions are high pressure areas as the amount of sunlight here is less than the tropical region. So, wind blows from polar regions to tropical regions.

  • Then comes the Earth’s movement, which is west to east. The Earth’s rotation on its axis causes deflection of the wind (in the tropical region as the speed of spinning of Earth is higher compared to polar sides due to its spherical shape — blowing from both the polar regions. Wind coming from the Arctic is deflected to the right while Antarctic wind deflects to the left side.
  • So, the wind is already blowing in one direction. But when it reaches the warmer place, cool air starts getting attracted to the centre to fill the gap. So while moving to the centre, cool air keeps getting deflected resulting in circulation of wind movement — this process continues until the cyclone hits the land.

 

What happens when a cyclone hits the land?

Cyclone dissipates when it hits the land as the warm water that rises and creates space for cool water is no longer available on land. Also, the moist air that rises up forms clouds leading to rains that accompany gusting winds during cyclones.

 

Insta Curious:

Do you know the differences between Supercell and Mesocylone? Reference

 

InstaLinks:

Prelims Link:

  1. Factors responsible for the genesis of cyclones.
  2. Naming of cyclones in various regions of the world.
  3. Why are there more cyclones in Eastern coast of India?
  4. What is coriolis force?
  5. What is the latent heat of condensation?

Mains Link:

Discuss the factors responsible for the formation of tropical cyclones.

Sources: Indian Express.