• Cyclones are centres of low pressure surrounded by closed isobars and having increasing pressure outwards.
  • As air enters an area of low pressure from all directions, the Coriolis Effect bends the direction of the wind to the right of its path.
  • This creates a counter clockwise rotation around the low and convergence near the centre of the system. As the air collides near the centre it is forced aloft where divergencetakes air away from the centre of the system.
  • A Cyclone is a system of low level convergence and high level divergence with a rising column of air in the centre of the rotating air mass. If the upper air is not diverging then there cannot be a cyclone present.

Cyclones are broadly of two types:

  1. a) Temperate cyclones ( caused in middle and high latitudes, thus does not occur in India)
  2. b) Tropical cyclones.

Tropical Cyclones

  • Cyclones developed in the regions between the Tropic of Cancer and Tropic of Capricorn, are called tropical cyclones.
  • The weather conditions of low latitudes, mainly rainfall regimes are largely controlled by tropical cyclones.
  • Tropical cyclones usually develop in summer season in the vicinity of Inter-Tropical Convergence Zone (ITCZ)over warm ocean surface.
  • Tropical cyclones are one of the mechanisms by which surface heat energy is redistributed from the equator to the poles.

Conditions necessary for development

  • Tropical cyclone is like a heat engine which is energized by latent heat of condensation. Generally, tropical cyclones are formed due to low pressure of thermal origin.
  • The conditions favourable for the formation and intensification of tropical cyclone storms are:
    • Large sea surface with temperature higher than 27° C
    • Presence of the Coriolis force
    • Small differences in the vertical wind speed
    • A pre-existing weak- low-pressure area or low-level-cyclonic circulation
    • Upper divergence above the sea level system
  • Having these conditions met is necessary, but not sufficient as many disturbances that appear to have favorable conditions do not develop.

Cyclone in India

  • India has a very long coastline which is exposed to tropical cyclones arising in the Bay of Bengal and Arabian Sea.
  • Indian Ocean is one of the six major cyclone-prone regions in the world. In India cyclones occur usually in April-May, and also between October and December.
  • The Eastern coastline is more prone to cyclones as about 80 percent of total cyclones generated in the region hit there.
  • The worst hitting cyclones have been the Andhra Pradesh cyclone of November 1977 and the super cyclone of Odisha in the year 1999.
  • The impact of the cyclones is mainly confined to the coastal districts, the maximum destruction being within 100 Km. from the centre of the cyclones and on either side of the storm track.
  • The principal dangers from a cyclone include the gales and strong winds; torrential rain and high tidal waves (storm surges).
  • Most casualties are caused by coastal inundation by tidal waves and storm surges.


Destruction caused by Cyclones:

  • There are three elements associated with cyclones which cause destruction during its occurrence. These are:
      • Strong Winds/Squall:
      • Torrential rains and inland flooding:
      • Storm Surge:


Benefits of Tropical Cyclones:

  • Although Tropical cyclones are known for destruction they cause, when they strike they also bestow certain benefits to the climatic conditions of that area such as
      • Relieve drought conditions.
      • Carry heat and energy away from the tropics and transport it towards temperate latitudes, thus helps to maintain equilibrium in the Earth’s troposphere and
      • Maintain a relatively stable and warm temperature worldwide.

Management of Cyclones:

  • There are many structural and non-structural measures for effective disaster management of cyclones.
  • The structural measures include construction of cyclone shelters, construction of cyclone resistant buildings, road links, culverts, bridges, canals, drains, saline embankments, surface water tanks, communication and power transmission networks etc.
  • Non-structural measures like early warning dissemination systems, management of coastal zones, awareness generation and disaster risk management and capacity building of all the stakeholders involved.
  • These measures are being adopted and tackled on State to State basis under National Cyclone Risk Mitigation Project (NCRMP) being implemented through World Bank Assistance.
Section : Environment & Ecology