What is Madden Julian Oscillation that is triggering anomalous rainfall in Kerala now

Kerala is currently witnessing a rain pattern, which is quite closer to being anomalous. Though variations in the climate pattern over the region has been emphatic in recent years, the present weather conditions have been strangely uneven over past few weeks. Met scientists have attributed this weather to a climatic phenomenon called Madden Julian Oscillation.

What is Madden Julian Oscillation
In 1971, Dr Roland Madden and Dr Paul Julian with the American National Center for Atmospheric Research (NCAR) discovered a peculiar weather phenomenon while studying tropical wind and atmospheric pressure patterns. They found that there was a regular oscillation of winds between Singapore and Canton Island. The climactic phenomenon named after the researchers as Madden-Julian Oscillation (MJO) is best understood in juxtaposition with the pattern called En Nino and the Southern Oscillation (ENSO), which impact the global seasonal-structure as well as regional weather patterns.

The intraseasonal variation is common in tropical atmospheres and is triggered by a motile pressure-variation current that is propagated eastwards above the warm parts of Indian Ocean and Pacific Ocean. It is in sharp contrast with the standing pattern of ENSO. The Madden–Julian oscillation is estimated to move at a speed between 14 to 29 kmph bringing in unusual rain and storm, which is categorised as enhanced and suppressed rainfall.

The moving disturbance of clouds, rainfall and wind moves ahead in the eastward direction across the planet through the tropical regions. It is said to take 30 to 60 days on average. Unlike ENSO, which persists for several seasons, MJO is considered as an intraseasonal climate variation that may vary on a weekly basis.

How does MJO bring in rain
The two phases of MJO are the opposing enhanced convective rainfall and suppressed convective rainfall. It's these opposite changes in clouds that direct the disturbances to move eastward. When winds converge on the surface of the Indian Ocean, the air surges up, diverges at the top and condenses again causing rain. Meanwhile, in the suppressed convective phase just the opposite happens. The winds converge on top of the west-central Pacific Ocean and the air drops down and dries suppressing the rain.

When MJO moves forward to the east, the tropical cyclone activity also shifts accordingly. And, there is a strong yearly variation in the MJO activity identified by long periods of strong activity followed by weak or no oscillation activity. Usually, the anomalous rainfall is first evident over the western Indian Ocean, and is evidently active while moving across warm ocean waters of the western and central Pacific regions. In the Bay of Bengal, the MJO activity causes cyclones and depressions culminating the effect in the Indian subcontinent.