Context: The Cyclonic Storm ‘HIKAA’ arrived over the northeast and adjoining east-central Arabian sea recently.
Prelims: Current events of national and international importance.
Mains: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone, etc.
What are tropical cyclones?
Tropical cyclones are regarded as one of the most devastating natural calamities in the world. They originate and intensify over warm tropical oceans. These are ferocious storms that originate over oceans in tropical areas and move over to the coastal areas causing violent winds, very heavy rainfall, and storm outpourings.
The main features of tropical cyclones are as follows:
- Size and Shape: Tropical cyclones have symmetrical elliptical shapes (2:3 ratio of length and breadth) with steep pressure gradients. They have a compact size—80 km near the center, which may develop up to 300 km to 1500 km.
- Wind Velocity and Strength: Wind velocity, in a tropical cyclone, is more in poleward margins than at center and is moreover the oceans than over land masses, which are scattered with physical barriers. The wind velocity may range from nil to 1200 km per hour.
- Path of Tropical Cyclones: These cyclones start with a westward movement but turn northwards around 20° latitude. They turn further north-eastwards around 25° latitude, and then eastwards around 30° latitude. They then lose energy and subside. Tropical cyclones follow a parabolic path, their axis being parallel to the isobars.
Coriolis force or earth’s rotation, easterly and westerly winds influence the path of a tropical cyclone.
Tropical cyclones die at 30° latitude because of cool ocean waters and increasing wind shear due to westerlies.
Conditions for the formation of Tropical Cyclone:
The conditions which favour the formation and intensification of tropical cyclone storms are:
- Large sea surface with a temperature higher than 27° C
- Presence of the Coriolis force
- Small differences in the vertical wind speed
- A pre-existing weak- low-pressure area or low-level-cyclonic circulation
- Upper divergence above the sea level system
How are tropical cyclones named?
- Tropical cyclones and subtropical cyclones are named by various warning centers to provide ease of communication between forecasters and the general public regarding forecasts, watches, and warnings. The names are intended to reduce confusion in the event of concurrent storms in the same basin. Generally, once storms produce sustained wind speeds of more than 33 knots (61 km/h; 38 mph), names are assigned in order from predetermined lists depending on which basin they originate.
- There is a strict procedure to determine a list of tropical cyclone names in an ocean basin(s) by the Tropical Cyclone Regional Body responsible for that basin(s) at its annual/biennial meeting.
- There are five tropical cyclone regional bodies, i.e. ESCAP/WMO Typhoon Committee, WMO/ESCAP Panel on Tropical Cyclones, RA I Tropical Cyclone Committee, RA IV Hurricane Committee, and RA V Tropical Cyclone Committee.
- The WMO/ESCAP Panel on Tropical Cyclones at its twenty-seventh Session held in 2000 in Muscat, Sultanate of Oman agreed in principle to assign names to the tropical cyclones in the Bay of Bengal and the Arabian Sea. After long deliberations among the member countries, the naming of the tropical cyclones over the north Indian Ocean commenced from September 2004. Eight countries — India, Pakistan, Bangladesh, Maldives, Myanmar, Oman, Sri Lanka, and Thailand participated in the panel and came up with a list of 64 names.
- The Panel member names are listed alphabetically country wise. The names will be used sequentially column-wise. For instance, the first name will start from the first row of column one and continue sequentially to the last row in column eight. For example, Onil, Hibaru, Pyar, Baaz and so on.
- In the event of a tropical cyclone/storm, the Regional Specialized Meteorological Centre, New Delhi, selects a name from the list.