Different Responses of the Madden‐Julian Oscillation to the Fast and Slow Decaying El Niño in Spring

This study investigates the modulation of the Madden‐Julian Oscillation (MJO) by El Niño during decaying springs, using reanalysis data. El Niño events are categorized into fast‐decaying (FD) and slow‐decaying (SD) types based on their decaying rate. In FD El Niño decaying springs, MJO circulation and convection weaken significantly over the central Pacific. In contrast, they are substantially enhanced under SD El Niño conditions. The stronger westerly anomalies, positive moisture anomalies, and anomalous ascending motion over the central Pacific induced by SD El Niño result in a weaker low‐frequency background moisture zonal gradient and a stronger MJO circulation. As a result, both zonal and vertical moisture advection are much stronger under SD El Niño conditions, leading to more pronounced lower‐tropospheric moistening east of the MJO convection center. Thus, MJO activity is enhanced over the central Pacific.