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

Topics: GS-I: Salient Features of World Physical Geography • GS-I: Important Geophysical Phenomena