Successive MJO propagation in MERRA‐2 reanalysis

Composite circumnavigating Madden‐Julian oscillation (MJO) events in Version 2 of the NASA Modern Era Reanalysis for Research and Applications (MERRA‐2) reanalysis propagate as convectively coupled Kelvin waves over the Western Hemisphere and moisture waves like that described by Adames and Kim (2016) over the warm pool. Estimated zonally variable phase speeds of coupled Kelvin waves in the tropics are calculated by determining the “effective static stability” experienced by the wave. The wave is structured similarly to a classically derived deep tropospheric Kelvin wave, and its phase speed is up to 33 m s−1 or 40 m s−1 over the central/eastern Pacific or Atlantic/equatorial Africa, respectively, during boreal winter. Theoretically, estimated phase speeds of convectively coupled Kelvin waves over the tropical warm pool are greater than 15 m s−1, much faster than the propagation of the reanalyzed MJO. A complete theory for MJO propagation around the globe must allow both coupled Kelvin waves and moisture waves. Key Points The MJO propagates like a convectively coupled Kelvin wave over the Western Hemisphere A holistic MJO theory must accommodate moisture waves and convectively coupled Kelvin waves Propagation is much slower over Pacific for strong MJO events during boreal summer