News Excerpt:

The India Meteorological Department (IMD) has issued an “orange” alert for Tamil Nadu and coastal and interior Andhra Pradesh due to the potential landfall of cyclone Michaung.

Cyclone:

• It is a large-scale system of air that rotates around the centre of a low-pressure area.
• It is usually accompanied by violent storms and bad weather.
• As per the National Disaster Management Authority (NDMA)-
• A cyclone is characterised by inward spiralling winds that rotate anticlockwise in the northern hemisphere and clockwise in the southern hemisphere.
• It classifies cyclones broadly into two categories: tropical cyclones and extratropical cyclones.

Tropical cyclones:

• These develop in the regions between the Tropics of Capricorn and Cancer.
• They are the most devastating storms on Earth.
• According to the US National Oceanic and Atmospheric Administration (NOAA)-
• Such cyclones develop when thunderstorm activity starts building close to the centre of circulation, and the strongest winds and rain are no longer in a band far from the centre.
• The storm's core turns warm, and the cyclone gets most of its energy from the “latent heat” released when water vapour that has evaporated from warm ocean waters condenses into liquid water.
• Warm fronts or cold fronts are not associated with tropical cyclones.
• Tropical cyclones have different names depending on their location and strength.
• For instance, they are known as hurricanes in the Caribbean Sea, the Gulf of Mexico, the North Atlantic Ocean and the eastern and central North Pacific Ocean. In the western North Pacific, they are called typhoons.
• The conditions favourable for the formation and intensification of tropical storms are -
• Large sea surface with a temperature higher than 27° C.
• Presence of the Coriolis force.
• Small variations in the vertical wind speed.
• A pre-existing weak low-pressure area or low-level-cyclonic circulation.
• Upper divergence above the sea level system.

Extratropical cyclones:

• Also known as mid-latitude cyclones, extratropical cyclones occur outside the tropics, i.e., beyond the areas that fall under the Tropic of Cancer and the Tropic of Capricorn.
• According to the US National Oceanic and Atmospheric Administration (NOAA)-
• They have cold air at their core and derive energy from releasing potential energy when cold and warm air masses interact.
• Such cyclones always have one or more fronts connected to them.
• A front is a weather system that is the boundary between two kinds of air masses, where one front is represented by warm air and the other by cold air. 
• Such cyclones can occur over land and ocean

Prelims PYQ

Q. In the South Atlantic and South Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the main reason behind this? (UPSC 2015)

(a) Sea Surface temperature are low

(b) Inter Tropical Convergence Zone seldom occurs

(c) Coriolis force is too weak

(d) Absence of land in those regions

Mains PYQ

Q. Discuss the meaning of colour-coded weather warnings for cyclone prone areas given by India Meteorological Department. (UPSC 2022)

Q. Tropical cyclones are largely confined to South China Sea, Bay of Bengal and Gulf of Mexico. Why? (UPSC 2014)