资源环境科技发展态势分析平台

Recent studies suggest that frequency of active phases of the Madden-Julian Oscillation (MJO) over the Maritime Continent and western Pacific, that is, the MJO Phases 4-6 defined by the real-time multivariate MJO (RMM) index, has increased in recent winters. A robust positive trend in MJO Phase 4-6 days during 1979-2015 winters is confirmed in this study. Our analyses, however, suggest that this trend could be exaggerated due to the blended low-frequency variability signals in the RMM. When the winter RMM is reconstructed using anomalous fields after removing their winter mean instead of the previous 120-day mean as for the original RMM, the robust trend in MJO Phase 4-6 days can no longer be detected. Therefore, cautions need to be exercised when applying the RMM for studies on the low-frequency variability and climate trend in MJO activity and using the derived MJO variability to interpret associated changes in climate systems.