Cyclones – UPSC GS1

What is polar front? How does cyclone develop along this front? Describe the weather condition associated with it. (150 Words)
A polar front is the boundary between the polar cell and the ferrel cell in each hemisphere i.e. North and South. According to the polar front theory the development of cyclone along this front occurs in the mid latitudes boundaries between warm tropical and cold air.
The collision of the two air masses results in the uplift of the warm air into the upper atmosphere creating a cyclonic spin around a low pressure center. This cyclone is usually known as mid- latitude cyclones because of its usual occurrence in the mid latitude. The life cycle of the storm is known as cyclogenesis. The weather condition associated with it are:
  • It causes stormy weather in winter mostly in East Green land ,Canada and United States.
  • It also causes chill biting blizzards at minus degree Celsius.
  • It is also responsible in creating different types of precipitation which include rain, freezing rain, hail ,sleet, snow pellets and snow.
  • When the storm is near its end stage which usually occurs in east green land the cold front catches up with the warm front causing a condition called occlusion.
  • The movement of the weather system is controlled by the polar jet stream in the troposphere.


Discuss critically the characteristics of tropical cyclones and analyse the extent to which they differ from the temperate cyclones. (150 Words)
Tropical cyclone develops between tropics of Capricorn and Cancer. Their size varies considerably and they advance with varying velocities. They move with vigorous speed and high velocity over the oceans but become weak and feeble while moving over land. The center of cyclone is characterized by extremely low pressure.
There is no temperature variation in their different parts. Mostly, rainfall cells are same. The tracks of tropical cyclones vary considerably in different parts. Normally they move from east to west under the influence of trade winds. They mainly occur in summer.
Temperate Cyclones differs from tropical cyclones in following ways:
  1. They are found on land and sea.
  2. They have a low pressure gradient. Their wind speed is low and never strong.
  3. They occupy areas measuring thousands of square kms. They travel from west to east. Rainfall is slow, but sometimes heavy showers takes place and continues for days.
  4. There are two fronts in energy Cyclones. More cyclones are produced in winter than in summer.
  5. The directions of wind are rapidly changed at the front. Veering and backing of winds take place.


Why there are fewer cyclones over the Arabian Sea as compared to the Bay of Bengal? Why there are very few Tropical Cyclones during southwest monsoon season? (150 Words)
Cyclones are fed by availability of water vapour in the atmosphere. The amount of water vapour in the atmosphere depends on the difference in temperature between the water surface and the air.
The Bay of Bengal has a lot of fresh water due to the major rivers in the region. Since freshwater is lighter than the salty waters in the Bay, it forms a thin layer on the surface. This thin layer of fresh water is heated more easily than the extremely salty waters in the Arabian Sea.
The tropical easterly jet stream extends far to the north of Tibet and the air flow is roughly along the Kolkata-Bangalore axis. These upper air easterlies descend into the permanent high pressure area formed over the southern Indian Ocean. The Tropical Easterly Jet (TEJ) shifts its position with the position of the ITCZ. By the end of September it is firmly establishes along an east to west direction and begin to flow towards the west, i.e. eastern coast on India.
Therefore, the Bay is more conducive to cyclone formation than the Arabian Sea.


Why is Coriolis Force zero at the Equator? Also explain why cyclones rotate clockwise in Northern Hemisphere? (150 Words)
The Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. The Coriolis effect is the one that makes low pressures rotate anti-clockwise in the northern hemisphere and clockwise in the southern. At the equator, the forces cancel each other out. That’s why the direction of rotation changes between the two hemispheres.
The reason is that the earth’s rotation sets up the Coriolis force that pulls the winds to the right in the Northern Hemisphere. So when a low pressure starts to form north of the equator, the surface winds will flow inward trying to fill in the low and will be deflected to the right and a counter-clockwise rotation will be initiated. The opposite (a deflection to the left and a clockwise rotation) will occur south of the equator. Thus, tropical cyclone in northern hemisphere rotates clockwise.