Tropical and Temperate Cyclones


Typical cyclones are elliptical arrangement of isobars having low pressure at the centre with a convergence of winds within them.

The wind direction in the cyclones is anti clockwise in the northern hemisphere and clockwise in the southern hemisphere.

Cyclones are of two types – the temperate or mid latitude cyclones and the tropical or low latitude cyclones.


Temperate Cyclones

Temperate cyclones are formed along a front in mid-latitudes between 35° and 65° N and S.

They blow from west to east and are more pronounced in winter season.

Atlantic Ocean and North West Europe are major regions of temperate cyclones.

They are generally extensive having a thickness of 9 to11 kilometers and with 1040-1920 km short and long diametres respectively.

Each such cyclone alternates with a high pressure anticyclone.

The weather associated with the cyclone is drizzling rain and of cloudy nature for number of days.

The anticyclone weather is sunny, calm and of cold waves.


Tropical Cyclones

Tropical cyclones are formed along the zone of confluence of north-east and south-east trade winds.

This zone is known as the Inter Tropical Convergence Zone (ITCZ).

Cyclones generally occur in Mexico, South-Western and North Pacific Ocean, North Indian Ocean and South Pacific Ocean.

These cyclones differ from temperate cyclones in many ways.

There are no clear warm and cold fronts as temperature seldom differs in Inter Tropical Convergence Zone.

They do not have well-defined pattern of winds and are energised by convectional currents within them.

Generally, these are shallow depressions and the velocity of winds is weak.

These are not accompanied by anticyclones.

The arrangement of isobars is almost circular.

These are not extensive and have the diametres of 160-640km. However, a few of them become very violent and cause destruction in the regions of their influence.

They are called hurricanes in the Carribean Sea, typhoons in the China, Japan and phillipines, cyclones in the Indian Ocean and willy-willies in Northern Australia.

Tropical cyclones often cause destruction on the coasts.

The steeper pressure gradient causing strong high velocity winds and torrential rainfall bursting upon a restricted area combine to create distructive storms.

However about 8 to 48 km. area around their centre called the eye of these stormy cyclones remains calm and rainless.

If this eye is detected, it is possible for the modern science to stop further development of these strong cyclones and thus protecting us from them.