Explained: Twin Tropical Cyclones 'Asani And Karim' Brewing In The Indian Ocean

Satellites crossing over the Indian Ocean are being entertained by two tropical cyclones, one on either side of the equator. Cyclones Asani and Karim, titled after the northern and southern hemispheres, are twin cyclones that formed at almost uniform longitude and are now sliding away.

What are twin cyclones?

The twin tropical cyclones are induced by Rossby waves near the equator, according to The Hindu. These symmetric tropical storms are created by the interaction of the wind and monsoon systems, as well as the Earth system.

Nasa Earth Observatory

Rossby waves are massive ocean surges with a wavelength range of 4,000¨C5,000 kms. These waves are termed after notable meteorologist Carl-Gustaf Rossby, who was the first to illustrate that all these waves emerged due to the earth's rotation, Debasis Sengupta, professor at the Centre for Atmospheric and Oceanic Sciences at the Indian Institute of Science, Bengaluru told The Hindu.

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

Both have a positive vortex value, which is a measure of spin. These Rossby waves frequently constitute twin cyclones.

Karim and Asani: The twin cyclone

In early May 2022, the Visible Infrared Imaging Radiometer Suite (VIIRS) recorded the two cyclones rotating in separate directions at approximately the same length from the equator.

The Coriolis effect¡ªa strength steered by Earth's axis that diverts sweeping winds in one way in the Northern Hemisphere as well as the opposite way in the Southern Hemisphere¡ªcauses cyclone winds to turn anticlockwise in the Northern Hemisphere but clockwise in the Southern Hemisphere.

AFP/Representational image

Tropical Cyclone Asani accelerated west-northwest from across the Bay of Bengal on, with peak consistent winds of 100-110 kmph (kilometers per hour). Asani is expected to decrease as it reaches southern India and turns northeast, maintaining the storm offshore all along the Andhra Pradesh-Odisha shoreline in the days ahead, according to the Indian Meteorological Department (IMD).

IMD has requested that all fishing activities in the most impacted regions be halted. Heavy rains are the most dangerous threat to the territory. Cyclone Asani might not even threaten India's east coast, however, its twin cyclone is moving clockwise just south of the equator in the Indian Ocean, while Asani turns counter-clockwise.

Tropical Storm Karim is roving in the open seas west of Australia.

Karim is a category II hurricane, with wind gusts of 112 kmph. Both originally started in the Indian Ocean. The cyclone poses no risk to major urban areas, but it may have an impact on Cocos Islands, a network of coral islands with a community of 600 people.

Seychelles, a South African nation, gave Karim its name. Sri Lanka proposed the term Cyclone Asani.

Are twin cyclones common?

The dual tropical cyclones turning north and near the equator are not uncommon!

Cyclone Fani was formed over the Bay of Bengal and Tropical Cyclone Lorna over the south part of the Indian Ocean in April 2019. Lorna was a Category 1 cyclone with an upper limit wind velocity of 70 kmph, whereas Fani became a particularly serious tropical cyclone storm with the highest wind speed of 250 kmph.

BCCL/Representational image

As shown in satellite pictures, such pairs of cyclone storms resemble reflective images of one another, rotating at approximately a similar longitude but in different directions. Such occurrences are prevalent in the western Pacific Ocean as well.

They do not emerge in the eastern Pacific or Atlantic Basins since tropical storms do not form in lower elevations south of the equator. Because of the Coriolis force, winds across low-pressure systems turn in circular paths in the Southern Hemisphere but anticlockwise in the Northern Hemisphere.

The Madden-Julian Oscillation (MJO), a disruption close to the tropical regions that flow east around the planet lasting approximately 30 to 50 days, triggered this set of cyclones, as it did in 2019. Westerly winds are believed to be powerful over the equatorial zone in the Indian Ocean for several weeks, most likely due to MJO.

The MJO is a big cloud and convection combination that spans 5,000-10,000 kilometres. It is made up of a Rossby wave and a Kelvin wave, both of which are types of wave structures found in the ocean.

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