Q:7:Differentiate between Tropical and Extra-Tropical cyclone.


Cyclone is a system in which winds are rotating inwards to an area of low barometric pressure, with an anticlockwise (northern hemisphere) or clockwise (southern hemisphere) circulation. In simple, it is a weather system in which winds rotate inwardly to an area of low atmospheric pressure.

There are two types of cyclones:

  1. Tropical cyclones
  2. and Extra Tropical cyclones (also called Temperate cyclones or middle latitude cyclones or Frontal cyclones or Wave Cyclones).
Tropical cycloneExtra-Tropical cyclone
  • Tropical cyclones develop in the region between the Tropics of Capricorn and Cancer.
  • These are intensified over warm tropical oceans and required temperature higher than 27° C, presence of the Coriolis force, small variations in the vertical wind speed, a pre-existing weak low- pressure area or low-level-cyclonic circulation and upper divergent above the sea level system. (Thermally originated).
  • Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large-scale destruction caused by violent winds, very heavy rainfall and storm surges. (high speed wind, violent storms)
  • Extra tropical cyclones occur in temperate zones and high latitude regions, though they are known to originate in the Polar Regions. (between 35° and 65° latitude in both the hemispheres)
  • It is in these latitude zones the polar and tropical air masses meet and form fronts. The temperature contrasts help to provide the forcing and instability needed for storm development in the form of frontal systems. (Frontal origin)
  • These are comparatively less-violent in nature. They are originated both over land and water. (Static, not violent)
  • Tropical cyclone winds are derived from the release of energy in the form of latent heat.
  • Tropical cyclones have their strongest winds near the surface of the Earth.
  • Tropical cyclones have acute low pressure in centre (average: 960 millibar)
  • Strong Pressure Gradient Force
  • Average diameter: 150-300 km
  • It moves from east to west (as trade wind)
  • The World Meteorological Organisation uses the term ‘Tropical Cyclone’ to cover weather systems in which winds exceed ‘Gale Force’ (minimum of 63 km per hour).
  • Prominent feature: Eye of cyclone (pressure lowest-air descends)
  • An extratropical cyclone gets its energy from the horizontal temperature contrasts that exist in the atmosphere.
  • Extratropical cyclones have their strongest winds near the tropopause.
  • Extra-tropical cyclones have low pressure in the centre but not acute low pressure.
  • Weak pressure gradient force
  • Very extensive system (800-1600 km diameter)
  • It moves from west to east (as westerlies wind)
  • As the pressure gradient is smaller, the velocity is moderate around 30 to 40 km per hour.
  • No such eye feature is found in extra-tropical climate.

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(the above pictures depicting both tropical and extra-tropical cyclone)

As far as the similarities between the two, tropical cyclones and extratropical cyclones are both symmetrical. They also have surface areas of low pressure with winds that rotate counter clockwise. Furthermore, both produce very heavy precipitation and often times results in flooding. Both tropical cyclones and mid-latitude cyclones can last for several days, and sometimes as long as a week or more.

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