What is Tropical Cyclone?
Tropical cyclone, representing a closed low pressure system generally having a diameter of about 650 km.
• Counterclockwise and clockwise air circulation in the northern and southern hemisphere respectively.
• Energy power equivalent to more than 10,000 atomic bombs which were hurled at Nagasaki in Japan during World War 2.
CHARACTERISTICS
• Size of tropical cyclones varies considerably. on an average, their diameters range between 80km and 300km but sometimes they become so small that their diameter is restricted to 50km or less.
• They advanced with varying velocities. Weak cyclones move at the speed of about 32km per hour while hurricanes attain the velocity of 180km per hour.
• It become more vigorous and move with very high velocity over the oceans but become weak and feeble while moving over land.
• The centre of the cyclone is characterized by extremely low pressure. The air pressure at the centre sometimes becomes as low as 650mb.
• Tropical cyclones are not always mobile. Sometimes they become stationary over a particular place for several days and yield heavy rainfall.
• They move east to west under the influence trade wind.
• The general direction is westerly up to 150 latitude from equator, pole ward between 150- 300, thereafter easterly.
• Tropical cyclones are confined to a particular period of the year, mainly during summer season.
• It become disastrous natural hazard because of their high wind speed of 180 &ndash 400km per hour, high tidal surges and high rainfall intensity.
TYPES OF TROPICAL CYCLONE
Tropical cyclones are generally classified into 4 major types.
Tropical disturbance
They are migratory wave like cyclones and are associated with easterly trade winds. They are also called easterly waves.
• Most of the easterly waves develop between 50 and 200 north latitudes in the western parts of the oceans.
• Sometimes they are so sluggish that they remain stationary over an area for several days.
• They are associated with heavy cumulus or cumulonimbus clouds which yield moderate to heavy rainfall with thunderstorms.
• They develop in the Caribbean sea and North Pacific ocean during summer months.
Tropical depressions
These are the centres of low pressure surrounded by more than one closed isobars and are very small in size.
• Velocity ranges between 40 &ndash 50 km per hour.
• They usually develop in the vicinity of intra tropical convergence but seldom develop in the trade wind belt.
• Tropical depressions generally influence the weather conditions of India and north Australia during summer.
• After being originated in the Bay of Bengal these cyclones move in north westerly and westerly directions.
Tropical storms
These are low pressure centres and are surrounded by closed isobars wherein winds move towards the centre with the velocity ranging between 40 to 120 km per hour.
• They frequently develop in the Bay of Bengal and Arabian sea during summer season.
• They also develop in the Caribbean sea and in the vicinity of Philippines.
Hurricanes and Typhoons
The extensive tropical cyclones surrounded by several closed isobars are called &ndash
Hurricanes in the USA
Typhoons in the China
Willy willy in Australia
Cyclones in Indian ocean
Bagulo in Philippines
Taifu in Japan.
• They move with average speed of more than 120km per hour.
• Hurricanes are most extensive and disastrous hazards of the entire atmospheric disturbance.
• The diameters range between 160 and 640 km.
• The pressure at the centre ranges between 900 to 950 mb. And the pressure gradient between the centre and outer margin ranges from 10 mb to 55 mb.
• The area of 6 to 48 km around the centre of Hurricane is generally dry and rainless and winds are feeble. This is called ‘eye of the cyclone’.
This article is shared by Priyanka Duta. Priyanka is a Guest Lecturer of Geography at New Alipore College, Kolkata.
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