Madden-Julian Oscillation
The Madden–Julian Oscillation (MJO) is a major fluctuation in tropical weather on weekly to monthly timescales. It can be characterized as an eastward propagating ‘pulse’ of cloud and rainfall near the equator that typically recurs about every 30 to 60 days.
Features
Key features of the MJO include:
- Eastward moving pulse of clouds, rainfall, winds and pressure
- Most prominent over the Indian and Pacific Oceans
- Complete cycle takes 30-60 days
- Causes variations in strength of monsoons
Phases
The MJO has two distinct phases as it propagates:
- Enhanced rainfall phase: Rising air motion increases clouds and rainfall
- Suppressed rainfall phase: Sinking air motion suppresses convection and rainfall
This cycling between enhanced and suppressed phases drives variations in tropical weather as it progresses eastward.
Effect on the Indian Monsoon
The MJO can significantly influence the Indian monsoon rainfall:
- Brings abundant rainfall when MJO rainfall phase is over Indian Ocean
- Leads to weak monsoon if longest cycle that misses the Indian Ocean
- Periodicity is key – shorter cycles associated with better monsoons
- Can compound impacts of El Niño and La Niña events
Forecasting and modeling the MJO is thus critical for monsoon predictions.
Difference from El Niño
While El Niño originates in the eastern Pacific, the MJO circumnavigates the globe. Also, El Niño is a seasonal phenomenon occurring every 2-7 years while the MJO persists year-round.
History
Meteorologists Roland Madden and Paul Julian identified the 30-60 day tropical wind and pressure oscillation patterns in 1971, which became known as the Madden-Julian Oscillation.
