Interdecadal variability of intensity of the Madden–Julian oscillation

Abstract

The interdecadal variability of intensity of the Madden-Julian oscillation (MJO) during boreal winter was investigated based on two reanalysis datasets (NOAA 20CR and ERA-20C). Both the reanalysis datasets reveal statistically significant power spectrum peaks at 12-20-year periods. A composite analysis shows that during the active interdecadal phase, eastward propagating MJO activity was strengthened over the equatorial warm pool expanded from the Indian Ocean (IO) to the western Pacific (WP). The cause of the enhanced MJO variability was attributed to the interdecadal change of background mean precipitation in situ. A further diagnosis shows that the increase of the background precipitation over the Maritime Continent and the WP was attributed to interdecadal warm sea surface temperature (SST) anomalies in situ, whereas the increase of the precipitation over the IO resulted from the local convective instability due to the increase of wind induced surface evaporation and moisture. The strengthened background precipitation impacted the MJO strength through the increase of the interdecadal background moisture in the lower and middle troposphere induced by anomalous vertical moisture advection. K E Y W O R D S interdecadal variability, Madden-Julian oscillation, modulation of MJO strength by interdecadal background mean state