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Nature Bytes: Odisha, West Bengal brace for Amphan

Amphan Cyclone

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Amphan Cyclone
Source: This May 17, 2020, satellite image released by NASA shows Amphan Cyclone over the Bay of Bengal in India. Amphan has intensified into a super cyclone and expected to make a landfall near Sundarbans, south of Kolkata, on Tuesday evening, May 19, 2020.

In News:

  • A rapidly intensifying Category 5 super cyclone ‘Amphan’ is moving across the Bay of Bengal and heading for the India-Bangladesh border.
  • According to the India Meteorological Department (IMD), the severe cyclonic storm is likely to make a landfall somewhere between Digha in West Bengal and Hatiya Islands in Bangladesh on 20th May 2020.

News Summary:

  • The super cyclone Amphan is expected to have windspeeds of 230-240 kmph gusting to 265 kmph, bringing heavy rainfall to coastal Odisha and West Bengal.
  • Any cyclone with windspeeds of over 220 kmph is categorised as ‘super cyclonic storm’.
  • Amphan will cross West Bengal – Bangladesh coasts between Digha (West Bengal) and Hatiya Islands (Bangladesh) close to Sundarbans.
  • However, by the time it makes landfall in West Bengal, Amphan is expected to tone down into a category 4 Extremely Severe Cyclonic (ESC) storm with wind speed of 165-175 kmph and gusting to 195 kmph.
  • Amphan will cause heavy to extremely heavy rainfall over Gangetic West Bengal and heavy to very heavy rainfall over north coastal Odisha on 19th May and 20th May 2020.
  • National Disaster Response Force (NDRF) teams have been deployed in West Bengal and Odisha to undertake massive evacuation of people and to handle any emergency situation.

What is a landfall?

  • Landfall is the event of a storm or waterspout moving over land after being over water.
  • A tropical cyclone is classified as making landfall when the center of the storm moves across the coast.

About: Tropical Cyclones

Cyclones:

  • Cyclones are centres of low pressure surrounded by closed isobars and having increasing pressure outwards.
  • As air enters an area of low pressure from all directions, the Coriolis Effect bends the direction of the wind to the right of its path.
  • This creates a counter clockwise rotation around the low and convergence near the centre of the system. As the air collides near the centre it is forced aloft where divergence takes air away from the centre of the system.
  • A Cyclone is a system of low level convergence and high level divergence with a rising column of air in the centre of the rotating air mass. If the upper air is not diverging then there cannot be a cyclone present.
  • Cyclones are broadly of two types:
    1. Temperate cyclones (caused in middle and high latitudes, thus does not occur in India).
    2. Tropical cyclones.
Cyclone Zones

Tropical Cyclones:

  • Cyclones developed in the regions between the Tropic of Cancer and Tropic of Capricorn, are called tropical cyclones.
  • The weather conditions of low latitudes, mainly rainfall regimes are largely controlled by tropical cyclones.
  • Tropical cyclones usually develop in summer season in the vicinity of Inter-Tropical Convergence Zone (ITCZ) over warm ocean surface.
  • Tropical cyclones are one of the mechanisms by which surface heat energy is redistributed from the equator to the poles.
  • Tropical cyclones are known by various names in different parts of the world.
  • In the North Atlantic Ocean and the eastern North Pacific they are called hurricanes, and in the western North Pacific around the Philippines, Japan, and China the storms are referred to as typhoons.
  • In the western South Pacific and Indian Ocean they are variously referred to as severe tropical cyclones, tropical cyclones, or simply cyclones.
  • All these different names refer to the same type of storm.

Conditions necessary for development:

  • Tropical cyclone is like a heat engine which is energized by latent heat of condensation.
  • Generally, tropical cyclones are formed due to low pressure of thermal origin.
  • The conditions favorable for the formation and intensification of tropical cyclone storms are:
    1. Large sea surface with temperature higher than 27° C.
    2. Presence of the Coriolis force.
    3. Small differences 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.
  • Having these conditions met is necessary, but not sufficient as many disturbances that appear to have favorable conditions do not develop.

Categories of Tropical Cyclones:

  • Category 1: Wind and gales of 90-125 kph, negligible house damage, some damage to trees and crops.
  • Category 2: Destructive winds of 125-164 kph. Minor house damage, significant damage to trees, crops and vehicles, risk of power failure.
  • Category 3: Very destructive winds of 165-224 kph. Some roof and structural damage, some caravans destroyed, power failure likely.
  • Category 4: Very destructive winds of 225-279 kph. Significant roofing loss and structural damage, vehicles blown away, widespread power failures.
  • Category 5: Very destructive winds gusts of more than 280 kph. Extremely dangerous with widespread destruction.
Tropical Cyclones Category

Cyclones in India:

Where do cyclones occur in India?

  • More cyclones occur in the Bay of Bengal than the Arabian Sea and the ratio is approximately 4:1.
  • An analysis of the frequency of cyclones on the east and west coasts of India between 1891 and 1990 shows that nearly 262 cyclones occurred on the east coast and 33 cyclones occurred on the west coast during this period.

Which states are the most cyclone-affected in India?

  • Indian sub-continent is the worst affected region of the world, having a coastline of 7516 kms.
  • There are 13 coastal states/Union Territories encompassing 84 coastal districts which are affected by cyclones.
  • Four states – Andhra Pradesh, Odisha, Tamil Nadu and West Bengal and one Union Territory – Pondicherry on the East Coast are most vulnerable to cyclone disasters.
  • Although cyclones affect the entire coast of India, the East coast is more prone as compared to the West coast.

Reason for frequent cyclones in Bay of Bengal:

  • Cyclones are more frequent in the Bay of Bengal region because:
    1. The warmer sea surface temperature of Bay of Bengal is an ideal platform for cyclones.
    2. The Bay of Bengal is adjacent to the northwest Pacific, which is one of the world’s most active basins for typhoons. Typhoons over the Northwest Pacific move across the South China Sea into the Bay of Bengal, intensifying into cyclones.
    3. The region receives the remnants of major landfalls in the Philippines, China and South Asia.
  • In contrast, Arabian Sea cyclones are mostly their own formations and they also generally move north-west, away from India’s west coast.

Also Read: Economic Bytes: Centre to pump 40,000 crore more into NREGA for FY21

Related Article: Environmental Bytes: How tropical cyclones are named?

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