Explain the formation of tropical cyclones. Also, illustrate the global distribution of these cyclones.

A tropical cyclone is a low pressure system over tropical or subtropical waters, with organised convection. The winds at lower level rotate clockwise (Southern Hemisphere) and anticlockwise (Northern Hemisphere).

Formation of tropical cyclones:

  1. Conditions conducive for formation of tropical cyclones:
    • Sea surface temperature must be greater than 270
    • Presence of high moisture content in atmosphere.
    • Presence of Coriolis force.
    • Pre-existing condition of weak low pressure area.
    • Upper air divergence above sea level.
  2. Process of formation:
    • Formed when convection causes warm, moist air above the ocean to rise.
    • The Coriolis Effect, made by earth’s rotation causes winds to rotate and warm air rises up quickly.
    • This warm moist air rises up and condenses to form large cumulonimbus clouds.
    • Release of energy from condensing of cumulonimbus clouds.
    • Continuous supply of moisture from Ocean, strengthens the cyclone.
    • Mature phase – strong spiral winds around the calm centre called ‘eye’.
    • Dissipates after landfall because supply of moisture is cutoff.

Global distribution:

  • Caribbean sea, Gulf of Mexico.
  • North-west Pacific Ocean.
  • Pacific Ocean, west of Mexico.
  • South Indian Ocean (near Madagascar)
  • North Indian Ocean and Bay of Bengal.
  • Arabian sea

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