Why in news?

Severe Cyclonic Storm Dana made landfall on the Odisha coast on the night of October 24. The storm made landfall at a speed of 100 to 110 kmph gusting at 120 kmph.

What’s in today’s article?

• Tropical Cyclone
• Naming of cyclone
• Landfall of cyclone

Tropical Cyclone

• About
  • Cyclones that develop in the regions between the Tropics of Capricorn and Cancer are called tropical cyclones. 
  • The World Meteorological Organisation uses the term 'Tropical Cyclone’ to cover weather systems in which winds exceed ‘Gale Force’ (minimum of 34 knots or 63 kph).
  • Tropical cyclones are the progeny of ocean and atmosphere, powered by the heat from the sea; and driven by easterly trades and temperate westerlies, high planetary winds and their own fierce energy.
• Formation of cyclones
  • 
  • Tropical Cyclone is a weather phenomenon, which is formed only over warm ocean waters near the equator.
• Characteristics of a Tropical Cyclone:
  • The centre of a cyclone is very calm and clear with very low air pressure. The average speed is 120 kmph.
  • They have closed isobars which leads to greater velocity.
    • Isobars are imaginary lines on a weather map that connect locations with equal atmospheric pressure.
  • They develop over oceans and sea only.
  • They move from east to west under the influence of trade winds.
  • They are seasonal in nature.
• Classification of cyclones
  • Cyclones are classified on the basis of wind speed by the Indian Meteorological Department (IMD):
    • Depression: Wind speeds of between 31–49 km/h
    • Deep Depression: Between 50-61 km/h
    • Cyclonic Storm: Between 62–88 km/h
    • Severe Cyclonic Storm: Between 89-117 Km/h
    • Very Severe Cyclonic Storm: Between 118-166 Km/h
    • Extremely Severe Cyclonic Storm: Between 167-221 Km/h
    • Super Cyclonic Storm: Above 222 Km/h
• Category of a tropical cyclone
  • The category of a tropical cyclone is determined by its sustained wind speed, as measured by the Saffir-Simpson Hurricane Wind Scale.
  • It is classified into five categories — Category 1 to Category 5.
  • While Category 1 tropical cyclones bring winds of 119 to 153 kmph, Category 5 tropical cyclones, which are the strongest, have winds of 252 kmph or higher.
    • Storms that reach Category 3 and higher are considered major tropical cyclones due to their potential to inflict significant damage.
• Tropical cyclones are known by different names in various regions
  • Hurricanes – In the in the West Indian islands in the Caribbean Sea and Atlantic Ocean.
  • Tornados - In the Guinea lands of West Africa and southern USA
  • Typhoons – In the Northwest Pacific Ocean, particularly affecting East and Southeast Asia (e.g., Japan, Philippines, China, Taiwan).
  • Cyclones – In the Southwest Indian Ocean (off the coast of Africa, Madagascar), the Southeast Indian Ocean, and the Southwest Pacific Ocean.
  • Willy-Willies – An informal term used for tropical cyclones in Australia.

Naming of Cyclones

• Cyclone Dana
  • The name Dana was suggested by Qatar to the World Meteorological Organisation/United Nations Economic and Social Commission for Asia and the Pacific (WMO/ESCAP).
• Process of naming
  • Worldwide, there are six regional specialised meteorological centres (RSMCs) and five regional Tropical Cyclone Warning Centres (TCWCs) mandated for issuing advisories and naming of tropical cyclones.

• The five regional Tropical Cyclone Warning Centres (TCWCs) are:
• ESCAP/WMO Typhoon Committee,
• WMO/ESCAP Panel on Tropical Cyclones
  • It is responsible for naming of cyclones in the Indian Ocean.

• RA(Regional Association) I Tropical Cyclone Committee,
• RA IV Hurricane Committee,
• RA V Tropical Cyclone Committee.

• IMD is one of the six RSMCs to provide tropical cyclone and storm surge advisories to under the WMO/Economic and Social Commission for Asia-Pacific (ESCAP).
  • WMO/ ESCAP is an inter-governmental regional body jointly established by the World Meteorological Organization (WMO) and the United Nations Economic and Social Commission for Asia-Pacific (ESCAP) in 1972.
  • Members – It has 13 countries as its members.
    • Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Qatar, Saudi Arabia, Sri Lanka, Thailand, United Arab Emirates and Yemen.
  • They contribute to a set of names which are assigned sequentially whenever a cyclonic storm develops.
    • The list of 169 cyclone names released by IMD in 2020 was provided by these countries — 13 suggestions from each of the 13 countries.
  • So, the tropical cyclones forming over different Ocean basins are named by the concerned RSMCs & TCWCs.

What is landfall of a cyclone?

• Landfall is the event of a tropical cyclone coming onto land after being over water.
• As per the IMD, a tropical cyclone is said to have made a landfall when the center of the storm – or its eye – moves over the coast.
  • The "eye" of a cyclone is a region of relatively calm weather found at the center of the storm.
  • Within the eye, winds are light and variable, often with clear or only partially cloudy skies.
  • The size of the eye can vary significantly, ranging from a few kilometers to over 50 kilometers (30 miles) in diameter in larger cyclones.
• During landfall, the outer bands of the storm may have already reached the coast, bringing strong winds, heavy rain, and storm surge.
• Landfall marks the moment when the cyclone officially reaches the land.
  • A landfall should not be confused with a ‘direct hit’, which refers to a situation where the core of high winds (or eyewall) comes onshore but the centre of the storm may stay remain offshore.