What are Twin Cyclones

The News

• A pair of tropical cyclones, one on each side of the equator out on a show for satellites passing over the Indian Ocean.
• In second week of May, the twin cyclones (Asani & Karim) were spinning at roughly the same distance from the equator, but in opposite directions.

Read about: Cyclone Mandous

FYI

• A cyclone’s winds spin counterclockwise in the Northern Hemisphere & clockwise in the Southern Hemisphere.
• This is due to the Coriolis effect—a force driven by Earth’s rotation that deflects prevailing winds in one direction in the Northern Hemisphere and the opposite direction in the Southern Hemisphere.

FYI – How are cyclones formed?

Favourable conditions for Cyclones

1. Continuous supply of Warm moist air
2. Above 26 degree water temperature
3. Coriolis force
4. Absence of wind shear
5. Pre existing Baroclinic instability

What are Twin Cyclones?

• Twin cyclones are a pair of tropical cyclones, one on each side of the equator which are mainly formed from one source of disturbance.
• An eastward moving tropical disturbance called the Madden-Julian Oscillation coupled with Rossby waves helped fuel the twin storms by promoting convection and strong westerly winds.

Rossby Waves

• Rossby waves are oceanic and atmospheric waves that naturally occur due to the Earth’s rotation. These waves affect the planet’s weather and climate.
• Unlike waves that break along the shore, Rossby waves are huge, undulating movements of the ocean that stretch horizontally across the planet for hundreds of kilometers in a westward direction. They are so large and massive that they can change Earth’s climate conditions, some waves have wavelengths of around 4,000–5,000 kilometres.

MJO – Madden Julian Oscillation

• Madden–Julian oscillation (MJO) is the largest element of the intraseasonal (30- to 90-day) variability in the tropical atmosphere.
• It was discovered in 1971 by Roland Madden and Paul Julian of the American National Center for Atmospheric Research (NCAR).
• It is a large-scale coupling between atmospheric circulation and tropical deep atmospheric convection.
• The Madden–Julian oscillation is a traveling pattern that propagates eastward, at approximately 4 to 8 m/s through the atmosphere above the warm parts of the Indian and Pacific oceans.

MJO – Madden Julian Oscillation

MJO – Madden Julian Oscillation

FYI

• Not all twin tropical cyclones are born from the Madden Julian Oscillation.
• Sometimes it is a mere Rossby wave with two vortices on either side which can create twin cyclones.

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