Twin cyclones

The symmetric tropical cyclones on either side of the equator are known as Twin Cyclones.

For example Cyclone Asani in the northern hemisphere and Cyclone Karim in southern hemisphere.

Cyclone Fani over the Bay of Bengal and Cyclone Lorna over the southern Indian Ocean.

Both the cyclones were formed at almost uniform longitude.

Causes

Twin cyclones are not really rare. The interplay of the wind and the monsoon system combined with the Earth system produces these synchronous cyclones.

Rossby waves are huge waves in the ocean with

wavelengths of around 4,000–5,000 kms.

The vortex in the northern latitudes moves anticlockwise and has a positive turn, whereas the one in the southern hemisphere turns clockwise and it has a negative spin.

This structure has a whirlpool in the northern latitudes and the other in the southern region which is mirror images of one another.

Both have a positive vortex value (measure of spin). Twin cyclones are formed from these Rossby waves.