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Summary
Geography Class 28

Revision of the previous class and Doubts are taken (05:12 PM)

Tropical cyclones (05:40 PM)

  • A Tropical cyclone is a low-pressure high velocity wind system originating within the tropics over the oceans.
  • Names in different regions:
    Indian Ocean

    Cyclone
    Atlantic ocean Hurricane.
    South china sea Typhoon
    Japan Taifu
    Philippines- Bagui
    Australia Willy Willy

Stages in Tropical cyclone (05:58 PM)

  • 7 stages of Tropical Cyclones
  • a)Temperature: Above 27-degree celsius over the ocean to ensure sufficient evaporation 
  • b)Depth of warm water: The 27-degree Celcius temperature should extend up to 60-70 meters in depth.
  • c)The humidity of Air: High Humidity of 50-60 % near the surface.
  • d)Minimum vertical wind shear: So that Humid and warm air is not swept away.
  • e)Coriolis force: It causes wind deflection therefore cyclones are developed only between 5 degrees North to 25 degrees North or 5 Degree south to 25 degrees south.
  • f)Pre Existing Low-pressure conditions: These get intensified to form Cyclones.
  • g)Upper Air divergence: Causing convergence near the surface.
  • In the above, the First 5 are the necessary condition.
  • Formation
  • A strong Convection results in the build-up of huge cumulonimbus clouds 
  • The Release of Latent heat provides more energy to the system supporting further strong Convection.
  • When the wind starts to descend along the sides the entire system is stabilized.
  • The Lateral winds near to the surface start to Rotate around the Low-pressure centre due to the Coriolis force.
  • After some time some of the dense air rising near the centre starts to descend resulting in the formation of an eye.
  • Once a cyclone is formed it moves under the influence of planetary winds and deflects toward the northwest direction.
  • When a cyclone makes landfall or enters the waters of higher latitude, It dissipates and comes to an end.

Structure of the Cyclone (07:18 PM)

  • Eye: It is the centre of the storm about 5-50 km in diameter with a clear sky, Calm conditions, Lowest pressure, and Highest temperature.
  • Eye wall: A wall of thick cumulonimbus clouds with 10-20 Km of width. It has the strongest wind in the cyclone. Thunderstorm occurs in this region due to intense convection.
  • Spiral bands: AKA rain bands or feeder bands extend for 100 km and lead to Galaxy like appearance.
  • Annular Zone: A Zone of suppressed cloudiness, High temperature, and low humidity.
  • Outer convective bands: At the edge of the main cloud mass with instability and convection

Naming System of Cyclones (07:25 PM)

  • In 2004, 8 countries of the Northern Indian Ocean agreed to have a common naming system for Cyclones. Each of the countries arranged them in alphabetical order.
  • And it was submitted in a set of 8 names.
  • The Regional Specialized Meteorological centre of WMO located in New Delhi maintains the list arranged in sequential order and assigns the names when the wind speed crosses 62km/hr.
  • The suggested names shall be neutral politically, Religiously, and Culturally as well as concerning Gender.
  • It should be easy to pronounce.
  • All the names in the earlier matrix, Expired in 2019, and a new matrix suggested by 13 countries was agreed upon effective from 2020.

Recurvature of the cyclones (07:46 PM)

  • When the Air currents in the local atmosphere push the air from the poles towards the Equator and interfere with Cyclone formation the Cyclone which is about to diminish gets more wind and deflects right or eastward under the influence of westerlies this phenomenon is known as Recurvature of the cyclones.
  • Recurvature is very difficult to predict, for example, Cyclone Ockhi of 2018.

Cyclones in the Indian Ocean (07:52 PM)

  • The number of Cyclones in the Bay of Bengal is more than in the Arabian sea in a Ratio of 4:1
  • Reasons:
  • Strong Wind shear in the Arabian sea
  • Temperature is higher in the  Bay of Bengal because more rivers enter the Arabian sea.

Colour-coded warning of IMD for Cyclones (07:57 PM)

  • It is used by IMD to signify the intensity of the situation and the warning associated with it
  • Four colours are used:
  • Green-No warning
  • Yellow-Be aware
  • Orange-Be prepared.
  • Red-Take Action
  • The objective is to alert people of Hazardous weather and prepare them for handling disaster situations.
  • It is Universal and issued during floods and heavier Rainfall for cyclones it is represented through a matrix.

Difference between Tropical and Temperate cyclones (08:01 PM)

  • You Can Refer to a chart Drawn in the class

The topic for the next class: Climatic Regions