Nature and causes of cyclone

September 26, 2014 4:02 PM |

4GA9936 CroppedCyclones, Hurricanes, Typhoons are the same. In the Indian seas it is called cyclones, in the Atlantic and eastern pacific ocean it is called Hurricanes, and in the western pacific it is called Typhoons.

In the Indian seas the various stages of development of a cyclonic storm are:-

  • Low pressure
  • Well marked low pressure
  • Depression (winds at 36-54 km/hr)
  • Deep Depression (winds at 54-66 km/hr)
  • Cyclonic storm (winds at 66-94 km/hr)
  • Sever cyclonic storm (winds at 94-126 km/hr)
  • Very sever cyclonic storm (winds at 126-240 km/hr)
  • Super Cyclonic Storm (winds at 240 km/hr and above)


Cyclones are formed from simple thunderstorms. However, these thunderstorms can  grow to cyclone strength only with warm ocean waters and moist atmospheric conditions. First of all, the ocean waters have to be warmer than 26 degrees Celsius . The heat and the moisture from warm waters is the source of energy for cyclones. Cyclones will weaken rapidly as they travel over land or colder ocean waters where there is less of warmth and moisture. Not only, to having warm ocean water, high humidity levels in the lower and middle troposphere are also required for cyclone development.

The vertical wind shear in a tropical cyclone's environment is also important. Wind shear is defined as the amount of change in the wind's direction or speed with increasing altitude.

A weak wind shear means that the cyclone grows vertically, and the latent heat from condensation is released into the air directly above the storm, aiding in its development. A stronger wind shear means that the cyclones become more slanted and the latent heat release is dispersed over a much larger area.

Stages of Development

Stages of Development from tropical depression to cyclone

A tropical disturbance in time can grow to a more intense stage by attaining a specified sustained wind speed.

Cyclones can last for more than a week, depending upon their sea travel duration. They usually give rise to a cluster of clouds bringing thunderstorms over the tropical ocean waters. Once a disturbance has graduated to a tropical depression status, the amount of time that its takes go to the next stage i.e. a tropical storm, usually half a day up to a couple of days. Also it may not happen at all. The amount of moisture and warmth of the ocean waters play a major role in determining these events.

Movement of Cyclones

Movement of Cyclones is steered by the zonal winds

The location of a cyclone in these wind belt decides its path. a cyclone originating in the easterly zonal wind area is driven westward by easterly winds in the tropics.

Most storms in the tropics move northwestward initially. They re-curve and travel northeastward on entering the region of strong westerlies.

The energy of the cyclone depends upon warm surface water of the tropics which is why cyclones dissipate rapidly over cold water. Also, the tropical storms do not develop in the proximity of equator.




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