Recently, Odisha has started preparing for a possible impact from Cyclone Dana in the coastal areas.

• The cyclone will be called “Dana” (a beautiful, precious pearl in Arabic), a name given by Qatar.
• Cyclone Dana is expected to make a landfall over the coastal states of West Bengal and Odisha

About Cyclones and Circulation Patterns

• A cyclone is a large-scale air mass rotating around a strong centre of low atmospheric pressure.
• These can be classified on the basis of their origin into tropical and extratropical cyclones.
• The wind around a low-pressure system in a cyclone is called cyclonic circulation, while around a high-pressure system, it’s called anticyclonic circulation.
• Types of Cyclones: Cyclones fall into two main categories
  • Tropical Cyclones: form between the Tropics of Capricorn and Cancer, developing over tropical or subtropical waters, where they organize into surface wind circulation patterns.
  • Extra-tropical cyclones (Temprate cyclones): typically occur in temperate and high-latitude regions, originating even from the Polar Regions.
• The table given below shows Pressure Systems and Wind Circulation Patterns.

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About Tropical Cyclone

• They are confined to the area lying between 30° N and 30° S latitudes in the atmosphere.
• Cyclones in India:  Tropical cyclones in the North Indian Ocean region develop during the pre-monsoon (April to June) and post-monsoon (October to December) periods.
• Required condition for a Cyclone:
• • Sea surface with high temperature (above 27^0).
  • Presence of coriolis effect for the creation of a cyclonic vortex.
  • Small variations in the vertical wind speed.
  • Latent heat for driving storm’s energy
  • Upper level divergence above the Sea Level System.

Characteristics of Tropical Cyclone

• It is a Violent Storms originate over oceans in tropical areas.
• Eye of a Tropical Cyclone: Eye has the lowest surface pressure and warmest temperatures and air descends at the centre. 
  • At the centre: Roughly circular calm area of comparatively light winds and fair weather 
  • Temperature: Only 0-2°C warmer at the surface in the tropical cyclone
• Driving Force: Latent Heat of Evaporation released by the condensation of moist rising air over oceans is the driving engine 
• Path: They move in a parabolic path towards the west under the influence of trade winds.

Cyclone Naming Protocol

• Rotational Basis: Cyclone names are assigned on a rotational basis by countries in a pre-determined list. 
• Regional Meteorological Centers: Worldwide, Six specialized regional meteorological centers (RSMCs) and five regional Tropical Cyclone Warning Centres (TCWCs) are mandated for issuing advisories and naming tropical cyclones.
• IMD’s Role: Indian Meteorological Department (IMD) is one of the RSMCs providing advisories and naming for the north Indian Ocean Including the Bay of Bengal and the Arabian Sea.
• Member Countries: IMD serves 13 member countries under the WMO/Economic and Social Commission for Asia-Pacific (ESCAP) Panel.
• • These are Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, United Arab Emirates, and Yemen.
• Current list has a total of 169 names including 13 names each from 13 WMO/ESCAP member countries. 

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Worldwide Terminology of Tropical Cyclones

• Typhoons: China Sea & Pacific Ocean; 
• Hurricanes: West Indian islands in the Caribbean Sea & Atlantic Ocean; 
• Tornados: Guinea lands of West Africa and southern USA; 
• Willy-willies: North-western Australia 

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