MaddenJulian

The Madden–Julian Oscillation, usually abbreviated MJO, is the most prominent mode of intraseasonal variability in the tropical atmosphere. Described by Roland Madden and Paul Julian in 1971, it is an eastward-moving pattern of enhanced and suppressed tropical rainfall, accompanied by characteristic changes in winds and atmospheric circulation. The MJO typically propagates from the western Indian Ocean across the Maritime Continent to the central and eastern Pacific, completing a cycle roughly every 30 to 60 days. Its amplitude and timing vary from year to year.

The MJO is understood as a large-scale coupling of atmospheric convection and circulation. It involves alternating regions of enhanced convection and suppressed rainfall, which produce distinct anomalies in outgoing longwave radiation, wind fields, and the Walker circulation. The cycle is commonly represented in an eight-phase diagram, with phases describing where convection is strongest as the disturbance moves eastward. Modern tracking relies on indices such as the Real-time Multivariate MJO index (RMM) that combine rainfall, and 850 hPa and 200 hPa wind anomalies to locate the phase and amplitude.

Impacts and relevance include modulation of tropical cyclone activity, rainfall distribution, and monsoon behavior across the tropics. The MJO interacts with the El Niño–Southern Oscillation and can influence its onset and strength on weekly to monthly timescales, while ENSO conditions can modify the propagation and expression of the MJO. Forecasting relies on satellite data and numerical models, with MJO indicators used to anticipate precipitation patterns, flood risk, and seasonal cyclone activity.