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Ecology & Environment
Mahesh

15/05/22 16:54 PM IST

Twin Cyclones

In News 
  • Recent satellite images have shown a pair of cyclones in the Indian Ocean region, one in the northern hemisphere and one in the southern hemisphere.
  • Named cyclone Asani and cyclone Karim respectively, these are twin cyclones originating in the same longitude and now drifting apart. 
Twin Cyclones 
  • The interplay of the wind and the monsoon system combined with the Earth system produces twin cyclones.
  • They are basically caused by equatorial Rossby waves.
  • Rossby waves are named for famous meteorologist Carl-Gustaf Rossby who was the first to explain that these waves arose due to the rotation of the Earth.
  • They are huge waves in the ocean with wavelengths of around 4,000–5,000 kilometres.
  • This system has a vortex in the northern hemisphere and another in the southern hemisphere, and each of these is a mirror image of the other.
  • The vortex in the north spins counterclockwise and has a positive spin, while the one in the southern hemisphere spins in the clockwise direction and therefore has a negative spin.
Twin Cyclones Formation 
  • When the vorticity is positive in both Northern and Southern hemispheres, as is the case with Rossby waves, the air in the boundary layer, whichis moist, is lifted slightly. That is enough to set off a feedback process.
  • When the air is lifted slightly, the water vapour condenses to make clouds. As it condenses, it lets out the latent heat of evaporation.
  • The atmosphere warms, this parcel of air rises, and a positive feedback is set off by this process.
  • The warmer parcel of air can rise further because it is lighter than the surrounding air, and it can form deeper clouds.
  • Meanwhile, moisture comes in from both sides. This leads to the formation of a cyclone if certain conditions are present.
Source-The Hindu 

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