MJOs

MJOs, or Madden–Julian Oscillations, refer to the dominant mode of intraseasonal variability in the tropics, characterized by eastward-moving regions of enhanced and suppressed convection that typically cycle every 30 to 60 days. The phenomenon, named after Roland Madden and Paul Julian who identified it in 1971, is most evident over the tropical Indian and Pacific Oceans and is a key driver of weather patterns in the equatorial belt.

The MJO arises from coupled interactions between atmospheric convection, moisture convergence, and large-scale circulations such as the Walker circulation. Its activity modulates tropical rainfall, wind, and divergence, and it interacts with other climate modes, including the El Niño–Southern Oscillation. The strength and impact of MJOs depend on the background state of the tropics and can influence regional climate extremes.

MJOs generally progress through a sequence of eight phases, moving from the western Indian Ocean toward the western Pacific. These phases correspond to shifts in convective activity and cloudiness, producing a traveling wave of enhanced and suppressed rainfall across the tropics. The exact footprint and timing can vary from event to event, and multiple MJOs can occur in a season with different amplitudes.

Observation and forecasting rely on multi-parameter indices, such as the Real-time Multivariate MJO index (RMM), which combines fields like outgoing longwave radiation and zonal wind anomalies at 200 hPa and 850 hPa. Monitoring is used to anticipate rainfall anomalies, monsoon behavior, and tropical cyclone development, with forecasts extending from several days to a couple of weeks. MJOs are an essential component of tropical climate variability and a continuing focus of weather and climate prediction research.