Twin Cyclones

• 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.

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.