UPSC Express

Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction caused by violent winds, very heavy rainfall and storm surges.

The conditions favourable for the formation of tropical cyclones are:

1. Large sea surface with temperature higher than 27° C
2. Presence of the Coriolis force
3. Small variations in the vertical wind speed
4. A pre-existing weaklow-pressure area or low-level-cyclonic circulation
5. Upper divergence above the sea level system

Structure of Cyclone:

• The Eye: A mature tropical cyclone is characterised by the strong spirally circulating wind around the centre, called the eye. The diameter of the circulating system can vary between 150 and 250 km. The eye is a region of calm with subsiding air.
• Eye Wall: Around the eye is the eye wall, where there is a strong spiralling ascent of air to greater height reaching the tropopause. The wind reaches maximum velocity in this region, reaching as high as 250 km per hour. Torrential rain occurs here.
• Rain Bands: From the eye wall, rain bands may radiate and trains of cumulus and cumulonimbus clouds may drift into the outer region. These bands are capable of producing heavy bursts of rain and wind, as well as tornadoes.

The cyclones become more severe and destructive with rising wind speed. In such situations, there is need for comprehensive disaster risk assessment and preparedness to reduce the damages and injuries to human and animal lives and other properties.