Global Geological And Climatic Events

Cyclone Dana

Note4Students

From UPSC perspective, the following things are important :

Prelims level: Tropical Cyclone, Landfall

Why in the News?

West Bengal and Odisha experienced heavy rainfall as Tropical Cyclone Dana is anticipated to make landfall later tonight.

What are Cyclones?

  • Cyclones are wind systems rotating inwardly towards an area of low atmospheric pressure. They are categorised into Tropical (Temperature-induced) and Temperate (extra-tropical) cyclones (airmass-induced).
  • Formation Conditions: Tropical cyclones originate in warm regions, requiring conditions such as
  1. Warm sea surface (> 27°C),
  2. Coriolis Force,
  3. Pre-existing low-pressure systems,
  4. Small vertical wind speed differences, and
  5. Upper air divergence.

Characteristics of Tropical Cyclones:

  • They form over warm water bodies due to energy derived from the condensation of warm water within cumulonimbus clouds.
  • Wind rotation is influenced by the Coriolis force, resulting in anti-clockwise rotation in the northern hemisphere and clockwise in the southern hemisphere.
  • By 30° latitude, the diminished warmth halts cyclone activity.

What is the “Landfall” of a Cyclone?

  • Landfall occurs when a tropical cyclone moves from the sea onto the land.
  • As per the IMD, a cyclone makes landfall when the centre of the storm, or its eye, crosses the coast.
  • Landfall should not be confused with a “direct hit”, where the eyewall (area of high winds) hits land but the eye of the cyclone remains offshore.
  • According to the National Oceanic and Atmospheric Administration (NOAA), a cyclone’s strongest winds may still impact land even if the centre of the storm does not reach the coast.

How long does a Cyclone Landfall last?

  • The duration of landfall typically lasts a few hours, depending on the wind speed and size of the storm.
  • For cyclone Dana, the landfall process is expected to last five to six hours with wind speeds around 125 km/h, impacting a wide region.
  • Cyclones usually weaken after landfall as they lose their moisture supply and experience increased surface friction.
  • While landfall is often the most destructive phase of a cyclone, it also signals the beginning of the cyclone’s dissipation.

PYQ:

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

(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

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