Search

Capabilities of 43 models of the Coupled Model Intercomparison Project Phase 6 (CMIP6) to simulate the Madden‐Julian Oscillation (MJO) were compared in this study. Models with higher MJO simulation skills reproduce organized large‐scale convection more frequently over the equatorial western Pacific (EWP), suggesting that MJO simulations are tightly connected to organization of large‐scale precipitation over the EWP. MJO simulation skills are not significantly correlated with the mean sea surface temperature (SST) over the EWP, but tightly connected to SST threshold for convection there. The top simulations exhibit lower SST threshold and more realistic SST‐precipitation relationship over the EWP, suggesting that convection can be organized more efficiently and intensified more rapidly with the increasing SST in these simulations. Our results emphasize that reproducing the relationship between SST and large‐scale precipitation over the EWP is critical to MJO simulations. Plain Language Summary: The Madden‐Julian Oscillation (MJO) is one of the most important tropical phenomena that modulate weather and climate systems at the intraseasonal time scales. However, accurately reproducing the MJO in global climate models remains a challenge. The eastward propagation of the MJO convection is usually not well‐reproduced in models. Comparing to observations, they tend to underestimate the occurrence frequency of individual MJO events with lower amplitude and shorter propagation range. This study explore whether the MJO simulations in models are linked to the relationship between sea surface temperature (SST) and large‐scale precipitation they reproduced. It was found that MJO simulation skills are greatly dependent on the organized large‐scale precipitation over the equatorial western Pacific. We further revealed that realistically reproducing the SST‐precipitation relationship over this region is critical for simulating the MJO in models. Key Points: Madden‐Julian Oscillation (MJO) simulation skills depend on organized large‐scale precipitation over the equatorial western Pacific (EWP) reproduced in modelsModels with higher MJO simulation skills exhibit lower sea surface temperature (SST) threshold for convection over the EWPRealistically reproducing the relationship between the SST and organized large‐scale precipitation is critical to MJO simulations [ABSTRACT FROM AUTHOR]

The eastward‐moving large‐scale convective system associated with the Madden‐Julian Oscillation (MJO) significantly impact global weather and climate. Recent decades have seen notable changes in the MJO's lifecycle due to non‐uniform tropical ocean warming, with the roles of natural climate variability and anthropogenic influence still requiring quantification. This study examines observed and projected long‐term changes in the MJO phase speed using four twentieth‐century reanalyses and CMIP6 simulations. We find a substantial increase in MJO phase speed in three reanalyses during the twentieth century (0.6–1.2 m s⁻1 century⁻1) and further increase in MJO phase speed during the twenty‐first century (0.3–1.5 m s⁻1 century⁻1), with notable multidecadal fluctuations. We attribute the overall acceleration of the MJO to the global warming‐driven increase in the meridional moisture gradient around the warm pool while attributing the multidecadal variability in the MJO phase speed to changes in the zonal moisture gradient associated with the Pacific Decadal Oscillation. Plain Language Summary: The Madden‐Julian Oscillation (MJO) is a crucial phenomenon in the tropics that impacts weather and climate globally. Although earlier research has discussed the observed changes in the MJO lifecycle due to tropical ocean warming, we still need to understand the role of natural climate variability associated with the MJO lifecycle. This study uses twentieth century reanalyses and future climate model projections to investigate how the speed of the MJO propagation has changed over time. We find that the speed of the MJO's eastward propagation has increased significantly in three of the reanalyses during the twentieth century and continues rising in the twenty‐first century. We believe that the overall increase in MJO speed is due to global warming, which enhances the meridional moisture difference around the warm pool area. We also noted significant multidecadal variation in the MJO propagation speed. The multidecadal changes in MJO speed are linked to variations in the zonal moisture difference influenced by the Pacific Decadal Oscillation. Key Points: Increasing MJO phase speed is identified in three twentieth‐century reanalysesWe attribute the MJO's eastward acceleration to the long‐term changes in the meridional moisture gradientPacific Decadal Oscillation influences multidecadal variation in the MJO phase speed [ABSTRACT FROM AUTHOR]