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  • Context (DTE | IE | IT): Twin cyclones Tej (over Arabian Sea) and Hamoon (over Bay of Bengal) developed over the north Indian ocean.
  • Twin cyclones are two tropical cyclones that develop simultaneously in the same region.

Cyclone Tej: Rare Twin Cyclonic Storms In Arabian Sea And Bay Of Bengal

Reasons for Formation of Twin Cyclones

Equatorial Rossby Waves

  • Oceanic and atmospheric rossby waves (or Planetary waves) occur due to the Earth’s rotation (Coriolis Force). These waves occur in rotating fluids.
  • Oceanic rossby waves are huge waves in the ocean with wavelengths of around 4,000–5,000 kms.
  • This system consists of a vortex in the northern hemisphere mirrored by a corresponding one in the southern hemisphere.
  • The northern vortex spins counterclockwise with a positive spin, while the southern vortex spins clockwise with a negative spin.
  • Both have positive value of the vorticity which is a measure of the rotation.

Madden-Julian Oscillation

  • MJO is an eastward moving trough (series of thunderstorms) in the tropics that recurs every 30 to 60 days.
  • The MJO consists of enhanced rainfall convective phase and suppressed rainfall convective phase.
  • During enhanced phase, increased cloud cover reduces solar radiation reaching the ocean surface, leading to cooling effects.
  • Conversely, during the suppressed phase, reduced cloud cover allows more solar radiation to penetrate the ocean, leading to warming of SSTs.

Fujiwhara Effect

  • When two tropical cyclones (or hurricanes) come in close proximity, they begin to rotate around a common midpoint (which looks like a dance). It is called the Fujiwhara Effect.
  • Conditions necessary for the effect to occur:
    • Two tropical cyclones formed around the same time in the same ocean region.
    • The distance between the centres (or eyes) of the cyclones is less than 1,400 km.
    • An intensity that could vary between a depression (wind speed under 63 km/hour) and a super typhoon (wind speed over 209 km/hour).

Fujiwhara effect Fujiwhara effect

For details on Fujiwhara Effect > PMF IAS August, 2023 CA

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