The MJO is a 30–60 day tropical oscillation — a coherent envelope of enhanced convection (rain) and suppressed convection propagating eastward around the equator at ~5 m/s
Indian Ocean — convection suppressed over Maritime Continent
Active MJO when amplitude > 1.0. Strong events reach 2.0–3.5.
• Enhanced Atlantic hurricane activity
• Wet anomalies East Africa
• Dry anomalies SE Asia
Discovery: Roland Madden and Paul Julian (1971) found a 40–50 day oscillation in rawinsonde data from Canton Island. The MJO drives variability in monsoon onset, tropical cyclone activity, and via teleconnections — North American weather. The Wheeler-Hendon (2004) RMM index uses OLR and 850/200 hPa winds projected onto two principal components to track MJO phase in real time.