Science for All | What is the Madden-Julian Oscillation?

Recently, the Bay of Bengal region saw a cyclone called Cyclone Asani that brought rain to parts of India’s east coast. This cyclone had a twin brother named Cyclone Karim in the southern hemisphere. Such double cyclones are said to be caused by the Madden-Julian Oscillation.

What is the Madden-Julian Oscillation or MJO as it is called?

The MJO is a large cluster of clouds and convection, perhaps 5,000-10,000 kilometers in size. Twin cyclones are sometimes born because of the MJO.

Not all tropical cyclones are born from the MJO. Sometimes they care about a simple Rossby wave with two vortices on either side of the equator; the MJO is a bit more complicated. The MJO is often said to be a coherent structure with a Kelvin wave to the east and a Rossby wave to the west behind. This is called the posterior side because the whole structure is moving eastwards at a slow speed of about 5 meters per second. This was discovered in the early 1970s.

The Madden Julian Oscillation is created in the Indian Ocean and decays near the International Date Line. But this is only the part of the wave that is damp. That is, the part in regions where the ocean is warm, so there are a lot of clouds. There is also the dry part of the MJO that goes around the Earth and comes back again. That is why it is called an oscillation. This repeats every 30 to 50 days. It is aperiodic, but it has a preferred time for recurrence. So in the winter season alone you have three of the MJOs that go by. “They are born in the western side of the Indian Ocean and then move east. You can see them going all the way to the middle of the Pacific Ocean, right up to the date line. They go all the way from 60 or 65 degrees east to about 150-180 degrees east, where the ocean is warm,” said Prof. Debasis Sengupta of Center for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru, who is an expert on climate studies. in the Bay of Bengal region. The warm pool in the ocean, which is the region associated with clouds, convection and heavy rain. Furthermore, the ocean is cool and the structure moves around the earth along the equator like a dry disturbance in the atmosphere. There is not enough moisture to support the clouds in these regions, where the ocean is cool. The dry MJO wave can actually be traced all over the world.

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