Tropical Cyclone

  • Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas.
  • It brings large-scale destruction caused by violent winds, very heavy rainfall and storm surges.
  • The winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Terminology

Tropical cyclones

It varies location to location. They are known as

  • Cyclones in the Indian Ocean
  • Hurricanes in the Atlantic
  • Typhoons in the Western Pacific and South China Sea, and,
  • Willy-willies in the Western Australia.

Naming Of Cyclones

  • Adopting names for cyclones makes it easier for people to remember, as opposed to numbers and technical terms.
  • Cyclones that form in every ocean basin across the world are named by the regional specialized meteorological centers (RSMCs) and Tropical Cyclone Warning Centres (TCWCs).
  • There are six RSMCs in the world, including the India Meteorological Department (IMD), and five TCWCs.
  • The IMD is mandated to naming of cyclones as well as issuing advisories to 13 countries in the region on the development of cyclones and storms, namely Bangladesh, India, Maldives, Myanmar, Oman, Pakistan, Sri Lanka, Thailand, Iran, Qatar, Saudi Arabia, United Arab Emirates and Yemen.

Conditions favorable for the formation

  • Large sea surface with temperature higher than 27° C;
  • Presence of the Coriolis force;
  • Small variations in the vertical wind speed;
  • pre-existing weak low-pressure area or low-level-cyclonic circulation;
  • Upper divergence above the sea level system.

Characteristics

Tropical cyclones

  • The energy that intensifies the storm comes from the condensation process in the towering cumulonimbus clouds, surrounding the centre of the storm.
  • With continuous supply of moisture from the sea, the storm is further strengthened. The more time they spend over the seas, the stronger they become.
  • On reaching the land the moisture supply is cut off and the storm dissipates. The place where a tropical cyclone crosses the coast is called the landfall of the cyclone.
  • The cyclones, which cross 20o N latitude generally, re-curve and they are more destructive.
  • A mature tropical cyclone is characterized by the strong spirally circulating wind around the centre, called the eye. The diameter of the circulating system can vary between 150 and 250 km. The eye is a region of calm with subsiding air.
  • Around the eye is the eye wall, where there is a strong spiraling ascent of air to greater height reaching the tropopause. The wind reaches maximum velocity in this region, reaching as high as 250 km per hour. Torrential rain occurs here.

From the eye wall rain bands may radiate and trains of cumulus and cumulonimbus clouds may drift into the outer region.