The Madden–Julian oscillation (MJO) is the largest element of the intraseasonal (30–90 day) variability in the tropical atmosphere. It was discovered in 1971 by Roland Madden and Paul Julian of the American National Center for Atmospheric Research (NCAR). It is a large-scale coupling between atmospheric circulation and tropical deep convection. Unlike a standing pattern like the El Niño Southern Oscillation (ENSO), the Madden–Julian oscillation is a traveling pattern that propagates eastward at approximately 4 to 8 m/s (14 to 29 km/h, 9 to 18 mph), through the atmosphere above the warm parts of the Indian and Pacific oceans. This overall circulation pattern manifests itself most clearly as anomalous rainfall.

The Madden–Julian oscillation (MJO) is the largest element of the intraseasonal (30–90 day) variability in the tropical atmosphere. It was discovered in 1971 by Roland Madden and Paul Julian of the American National Center for Atmospheric Research (NCAR). It is a large-scale coupling between atmospheric circulation and tropical deep convection. Unlike a standing pattern like the El Niño Southern Oscillation (ENSO), the Madden–Julian oscillation is a traveling pattern that propagates eastward at approximately 4 to 8 m/s (14 to 29 km/h, 9 to 18 mph), through the atmosphere above the warm parts of the Indian and Pacific oceans. This overall circulation pattern manifests itself most clearly as anomalous rainfall.