Cyclone Ditwah

Context:

Cyclone Ditwah weakened on Sunday while moving northward over the Bay of Bengal, parallel to Tamil Nadu and Puducherry coasts.

UPSC Relevance:

Geography

UPSC PYQ:

1. Consider the following statements:

1. Jet streams occur in the Northern Hemisphere only.
2. Only some cyclones develop an eye.
3. The temperature inside the eye of a cyclone is nearly 10°C lesser than that of the surroundings.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 and 3 only

(c) 2 only

(d) 1 and 3 only

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

About Cyclone:

Cyclones are rapid inward air circulation around a low-pressure area. The air circulates in an anticlockwise direction in the Northern hemisphere and clockwise in the Southern hemisphere.

•  The word Cyclone is derived from the Greek word Cyclos meaning the coils of a snake. It was coined by Henry Peddington because the tropical storms in the Bay of Bengal and the Arabian Sea appear like coiled serpents of the sea.

Several favorable environmental conditions:

• Low values (less than about 23 mph / 37 km/h) of vertical wind shear between the surface and the upper troposphere. Vertical wind shear is the change in wind speed with height.
• Warm ocean waters (at least 80°F / 27°C) throughout a depth of about 150 ft. (46 m).
• An atmosphere which cools fast enough with height such that it is potentially unstable to moist convection.
• Relatively moist air near the mid-level of the troposphere (16,000 ft. / 4,900 m).
• Generally, a minimum distance of at least 300 miles (480 km) from the equator.
• A pre-existing near-surface disturbance.

Stages of Formation: 

Formation and Initial Development Stage

• Cyclone formation depends on the transfer of water vapour and heat from the warm ocean to the atmosphere.
• Strong evaporation from the sea surface adds moisture and heat to the overlying air.
• Warm, moist air rises due to convection, forming large cumulus clouds.
• As the rising air cools, condensation occurs, releasing latent heat, which further fuels the system.
• This continuous heat release deepens the low-pressure zone, leading to the early structure of a developing cyclonic storm.

Mature Stage

• As the tropical storm intensifies, air rises violently in deep convective thunderstorms.
• At the tropopause level, the rising air spreads outward horizontally.
• This outward spreading of air creates a positive pressure (high pressure) at upper levels.
• The upper-level high pressure forces air to descend in the centre → Subsidence.
• Descending air warms by compression, forming the warm Eye (low-pressure centre).
• A mature cyclone displays a concentric pattern of giant, turbulent cumulonimbus cloud bands spiralling around the eye.
• Wind speeds are at their highest, and the cyclone reaches its maximum intensity.

Modification and Decay Stage

• A tropical cyclone begins to weaken when its main energy source — warm, moist air — is reduced or cut off.
• This happens when:
  • The cyclone makes landfall, where moisture availability is low, or
  • It travels over cold ocean waters, where evaporation is minimal.
• As a result:
  • The central low pressure rises,
  • The internal heat decreases,
  • The wind speeds gradually reduce.
• Eventually, the cyclone dissipates into a low-pressure area or depression.

Cyclone Ditwah:

• Sri Lanka Impact — Very High Casualties:
  • 334 dead, 370 missing due to heavy rain, landslides, and floods.
  • Most affected districts:
    • Badulla, Kandy, Nuwara Eliya, Matale
• These are hilly districts → vulnerable to landslides.