Anatomy of a cyclone

A FULLY DEVELOPED Tropical cyclone has a central

cloud-free region of calm winds,known as the “eye” of the cyclone,with a diameter varying from 10 to 50 km. Surrounding the eye is the “wall cloud region” characterised by very strong winds and torrential rain,which is about 10-150 km wide. Winds over this region rotate around the centre and resemble the “coils of a snake”. Wind speed falls off gradually away from this core region. The height of the cyclone is about 15 km. A mature cyclone releases energy equivalent to that of 100 hydrogen bombs.

THE WORD CYCLONE

Comes from the Greek ‘cyclos’,

meaning ‘coiling of a snake’. It was coined by Heary Piddington who worked as a rapporteur in Kolkata during the Raj. Tropical cyclones over the Atlantic are called hurricanes; those over the Pacific are called typhoons.

MAXIMUM SUSTAINED

Wind Speeds,mentioned by the

India Meteorological Department (IMD),is the strongest surface wind speed in a three-minute cycle within the cyclonic system at the standard height of 10 m (33 ft) in an unobstructed exposure. US National Hurricane Centre uses 1 minute averaging time for reporting sustained winds.

CLASSIFICATION OF

Low pressure systems in India moves from a ‘low pressure area’ with an associated wind speed of less than 17 knots (32 km/h) to a ‘supercyclonic storm’,where wind speeds reach over 119 knots (220 km/h). Phailin is a ‘Very Severe Cyclonic Storm’,with associated wind speeds of 64-119 knots (119-220 km/h).

OVER NORTH INDIAN

Ocean,tropical cyclones have

average radiuses of 300-600 km. The smallest ones have radiuses of between 50 km and 100 km,and the largest can have a radius of up to 2,000 km.

MOST INTENSE CYCLONE

Ever to hit India was the Orissa

supercyclone,which crossed the Orissa coast near Paradip on October 29,1999. It had an estimated sustained maximum surface wind speed of about 140 knots (260 km/h) at the time of landfall. The lowest estimated central pressure was 912 hPa.

LIFE OF A CYCLONE

Over the North Indian Ocean is

5-6 days. It has hurricane intensity for 2-4 days,as against the global average of 6 days. Two tropical cyclones that survived 14 days each in 1886 and 1964 were the longest lived tropical cyclones in Indian seas.

Source: IMD