Intensification of Westerly Wind Bursts Caused by the Coupling of the Madden‐Julian Oscillation to SST During El Niño Onset and Development

The Madden‐Julian Oscillation (MJO) plays an important role in El Niño dynamics in connection with westerly wind bursts (WWBs) that occur in the equatorial Pacific; however, our understanding of the relationship between these climate phenomena remains incomplete. Here, we use a Lagrangian Atmospheric Model (LAM) to examine the response of the MJO and resulting WWBs to sea surface temperature (SST) anomalies similar to those observed during the onset and development of El Niño. We find that when a localized SST anomaly (≤1°C) is imposed in the western‐central equatorial Pacific between December and April (mimicking El Niño onset), the MJO convective envelope shifts from the southern hemisphere toward the equator. When an SST anomaly (≤1.5°C) is imposed in the central‐eastern equatorial Pacific between May and November (mimicking El Niño development), the MJO weakens in the northwestern Pacific, but strengthens in the central equatorial Pacific. In both experiments, the ensuing changes enhance MJO activity along the equator, facilitating WWBs. Plain Language Summary The Madden‐Julian Oscillation (MJO) is an eastward propagating planetary‐scale envelope of clouds, heavy rainfall, and winds in the tropical atmosphere. It can contribute to the development of El Niño through the generation of westerly wind bursts (WWBs). El Niño is marked by anomalously warm sea surface temperature (SST) in the central and eastern equatorial Pacific, which has profound impacts on global weather patterns. WWBs are episodic bursts of strong westerly winds in the western‐central equatorial Pacific lasting several weeks and usually observed during the onset (spring) and development (summer) stages of El Niño. As WWBs contribute to the growth of El Niño and affect its predictability, it is important to understand the mechanisms of WWBs. In this study, we use a novel numerical model to investigate how WWBs are generated by the MJO and how this process is affected by El Niño‐related SST anomalies. We find that during the onset (development) stages of El Niño, positive SST anomalies in the western (central‐eastern) equatorial Pacific draw the MJO‐induced precipitation anomalies toward the equator, facilitating WWB generation. We also find that stronger MJO events tend to generate more intense WWBs. Our results can help improve the prediction of WWBs critical to El Niño development. Key Points The Madden‐Julian Oscillation convective envelope shifts from the southern hemisphere toward th