Editorial 2 : How the Madden-Julian Oscillation helped trigger the early onset of the monsoon
Context
The southwest monsoon arrived in Kerala on May 24, eight days earlier than the normal onset date, it reached Mumbai two weeks in advance on May 26.
The phenomenon behind
- Several large-scale atmospheric-oceanic and local factors developed and favoured the early monsoon onset but one of the key drivers was the Madden-Julian Oscillation (MJO), according to the India Meteorological Department (IMD).
- The phenomenon takes its name from the two scientists who identified it in 1971 — Roland Madden and Paul Julian.
What is MJO?
- The MJO is a moving system of winds, cloud, and pressure that brings rain as it circles around the equator.
- The system typically travels eastward at a speed of 4-8 metres per second. It goes around the globe in 30-60 days on average, but can sometimes take 90 days.
- As it moves, strong MJO activity often splits the planet into two parts — one in which the MJO is in active phase and brings rainfall, and the other in which it suppresses rainfall.
- In the active phase, MJO results in higher-than-average rainfall for that time of the year, while in the suppressed phase, the area receives less than average rainfall.
- An active phase is generally followed by a weak or suppressed phase, in which there is little MJO activity.
Typical Features of MJO
- The MJO is characterised by an eastward-moving ‘pulse’ of cloud, wind, and rainfall near the equator.
- The MJO typically recurs every 30 to 60 days.
- The MJO is most prominent over the Indian and Pacific Oceans.
- The MJO influences tropical and subtropical weather patterns, affecting rainfall and storm activity.
- The oscillation has distinct phases, each associated with weather patterns and cloud cover variations and precipitation variations.
Effect in tropical region
- The effect of the MJO is witnessed mainly in the tropical region, in the band between 30 degrees North and 30 degrees
- South of the equator, even though the mid-latitude regions in both hemispheres also feel its impact.
- India falls in this band. As the MJO cycle lasts only 30-60 days, there can be multiple MJO events in a season.
MJO and El Nino
- There is some evidence that the MJO and El Niño — the unusual warming of sea-surface Pacific waters off the South American coast — are correlated.
- Thus, strong MJO activity, like this year, is witnessed in a year of strong El Niño.
- However, the correlation is not exclusive: a strong El Niño year — the strength being a measure of the increase of temperature of sea surface water — is generally associated with a bad monsoon.
Influence on the Indian Monsoon
- The Indian Ocean Dipole (IOD), El Nino, and MJO are all oceanic and atmospheric phenomena that affect weather on a large scale.
- IOD only pertains to the Indian Ocean, but the other two affect weather globally up to the mid-latitudes.
- While the Indian Ocean Dipole (IOD) and El Niño remain fixed in their respective positions, the Madden-Julian Oscillation (MJO) is a traversing phenomenon that progresses through eight phases.
- When the Madden Julian Oscillation is over the Indian Ocean during the monsoon season, it enhances rainfall across the Indian subcontinent.
- On the other hand, when it witnesses a longer cycle and stays over the Pacific Ocean, the Madden Julian Oscillation brings bad news for the Indian Monsoon.
- It is linked with enhanced and suppressed rainfall activity in the tropics and is very important for the Indian monsoonal rainfall.
Conclusion
MJO significantly affects weather patterns on a global scale by modulating rainfall and storm activity across the tropics. Understanding the Madden Julian Oscillation behaviour is crucial for accurate weather forecasting, climate prediction, and managing the impacts of extreme weather events.