Cyclone Dana to Hit Odisha and West Bengal

Syllabus: GS1/ Geography

Context

• According to the Indian Meteorological Department Cyclone Dana will intensify into a severe cyclonic storm and make landfall in West Bengal and Odisha coast.

What is a Cyclone?

• A cyclone is a large-scale system of air that rotates around the center of a low-pressure area. 
  • It is usually accompanied by violent storms and bad weather. 
• A cyclone is characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
• The National Disaster Management Authority (NDMA) classifies cyclones broadly into two categories: extratropical cyclones and tropical cyclones.

What are Extratropical Cyclones?

• Extratropical cyclones also known as mid-latitude cyclones occur outside of the tropics. 
• They have cold air at their core, and derive their energy from the release of potential energy when cold and warm air masses interact.
• Such cyclones always have one or more fronts — a weather system that is the boundary between two different types of air masses.
  • One is represented by warm air and the other by cold air — connected to them, and can occur over land or ocean.

What are Tropical Cyclones?

• Tropical cyclones are those which develop in the regions between the Tropics of Capricorn and Cancer. 
  • They are the most devastating storms on Earth. 
• Such cyclones develop when thunderstorm activity starts building close to the center of circulation, and the strongest winds and rain are no longer in a band far from the center.
• The core of the storm turns warm, and the cyclone gets most of its energy from the “latent heat” released when water vapor that has evaporated from warm ocean waters condenses into liquid water, the agency added.
  • Moreover, warm fronts or cold fronts aren’t associated with tropical cyclones.
• Tropical cyclones have different names depending on their location and strength.
  • Hurricanes: Caribbean Sea, the Gulf of Mexico, the North Atlantic Ocean, and the eastern and central North Pacific Ocean. 
  • Typhoons: In the western North Pacific.

Favorable Conditions for Tropical Cyclones

• Very Large Body of water: It provides a continuous source of water to the storm.
• Presence of Coriolis force: It is caused by the Earth’s rotation, and is responsible for giving the cyclone its characteristic circular motion.
  • This force deflects the winds, making them spiral towards the low-pressure center of the storm.
• Pre-existing low-Pressure circulation: Tropical cyclones are defined by a low-pressure center, commonly referred to as the Eye of the Cyclone.
  • Surrounding this eye, air converges, rises, and cools, leading to the formation of clouds and heavy rainfall. 
• Warm Sea temperature:  The warm surface water  (above 26°C) heats the air above it, causing the air to rise and form the core of the storm. 

IMD Classification of Cyclones

• The India Meteorological Department (IMD) classifies cyclones based on the sustained wind speeds associated with them
  • Cyclonic Storm: 62-88 kmph
  • Severe Cyclonic Storm: 89-117 kmph
  • Very Severe Cyclonic Storm: 118-167 kmph
  • Extremely Severe Cyclonic Storm: 168-221 kmph
  • Super Cyclonic Storm: Greater than 222 kmph

Source: IE