Answer:
The atmospheric disturbances which involve a closed circulation about a low pressure centre, anticlockwise in the northern atmosphere and clockwise in the southern hemisphere, are called cyclones.
They fall into the following two broad categories: (a) Extra-tropical and (b) tropical cyclones. The differences between the two are stated below:
Tropical Cyclone
Origin It has thermal origin and derives its energy from the latent heat of condensation
Latitude It is confined to 10o – 300 N and S of equator.
Formation It requires sea surface temperature more than 26-27oC. It dissipates on reaching the land.
Size It is limited to small area. Its typical size is 100 – 500 kms in diameter. It varies with the strength of the cyclone.
Rainfall Rainfall is heavy but does not last beyond a few hours. If the cyclone stays at a place, the rainfall may continue for many days.
Wind Velocity Wind velocity is much higher (100 – 250 kmph)
Isobars Complete circles and the pressure gradient is steep.
Life time Doesn’t last for more than a week Calm region The center of a tropical cyclone is known as the eye. The wind is calm
at the center with no rainfall.
Influence of Jet streams
The relationship between tropical cyclones and the upper level airflow is not very clear.
Movement It moves from east to west
Temperate Cyclone
It has dynamic origin involving coriolis force and movement of air masses. The energy of a temperate cyclone depends on the densities of air masses.
It is confined to 350 – 650 N and S of equator. It is more pronounced in Northern hemisphere due to greater temperature contrast.
It can form both on land as well as seas. Its formation is due to frontogenesis.
It covers a larger area. Its typical size is 300 – 2000 kms in diameter
Rainfall is slow and continues for many days, sometimes even weeks.
Wind velocity is comparatively low. Typical range: 30 – 150 kmph.
Isobars are usually ‘V’ shaped and the pressure gradient is low.
Last for 2-3 weeks.
There is not a single place where winds and rains are inactive.
It has a distinct relationship with upper level air flow (jet streams, Rossby waves etc.)
It moves from west to east
