Cyclone Gulab crosses coast near Kalingapatnam in Andhra Pradesh

• Gulab was suggested by Pakistan.
• Cyclonic storm Gulab crossed the north Andhra Pradesh and south Odisha coast about 20 km north of Kalingapatnam, triggering widespread rain in the region.
• Cyclone ‘Gulab’ is likely to hit east coast of India.
• It is formed in the Bay of Bengal Region.

Cyclones formation:

• Cyclones are formed over the oceanic water in the tropical region.
• In this region, the sunlight is highest which results in warming of land and water surface. Due to warming of the surface, the warm moist air over the ocean rises upwards following which cool air rushes in to fill the void, they too get warm and rise — the cycle continues.

Classification:

• There are two types of cyclones:
• Tropical cyclones
• Extra Tropical cyclones (also called Temperate cyclones or middle latitude cyclones or Frontal cyclones or Wave Cyclones).
• The World Meteorological Organisation uses the term 'Tropical Cyclone’ to cover weather systems in which winds exceed ‘Gale Force’ (minimum of 63 km per hour).
• Tropical cyclones develop in the region between the Tropics of Capricorn and Cancer. They are large-scale weather systems developing over tropical or subtropical waters, where they get organized into surface wind circulation.
• Extra tropical cyclones occur in temperate zones and high latitude regions, though they are known to originate in the Polar Regions.

Tropical Cyclones:

• 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.
• Tropical Cyclones are one of the most devastating natural calamities in the world.
• Tropical cyclones originate and intensify over warm tropical oceans.
• The conditions favourable for the formation and intensification of tropical storms 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 weak low- pressure area or low-level-cyclonic circulation.
5. Upper divergence above the sea level system.

Stages of Formation: Tropical Cyclones

• The development cycle of tropical cyclones may be divided into three stages:
• Formation and Initial Development Stage
• The formation and initial development of a cyclonic storm depends upon the transfer of water vapour and heat from the warm ocean to the overlying air, primarily by evaporation from the sea surface.
• It encourages formation of massive vertical cumulus clouds due to convection with condensation of rising air above the ocean surface.
• Mature Stage
• When a tropical storm intensifies, the air rises in vigorous thunderstorms and tends to spread out horizontally at the tropopause level.
• Once air spreads out, a positive pressure at high levels is produced, which accelerates the downward motion of air due to convection.
• With the inducement of subsidence, air warms up by compression and a warm ‘Eye’ (Low pressure centre) is generated.
• The main physical feature of a mature tropical cyclone in the Indian Ocean is a concentric pattern of highly turbulent giant cumulus thundercloud bands.
• Modification and Decay
• A tropical cyclone begins to weaken in terms of its central low pressure, internal warmth and extremely high speeds, as soon as its source of warm moist air begins to ebb or is abruptly cut off.
• This happens after its landfall or when it passes over cold waters.