Investigating Recent Changes in MJO Precipitation and Circulation in Two Reanalyses

Abstract:

Recent work using CMIP5 models under RCP8.5 suggests that individual multimodel-mean changes in precipitation and wind variability associated with the Madden-Julian oscillation (MJO) are not detectable until the end of the 21st century. However, a decrease in the ratio of MJO circulation to precipitation anomaly amplitude is detectable as early as 2021-2040, consistent with an increase in dry static stability as predicted by weak-temperature-gradient balance. Here, we examine MJO activity in two reanalyses (ERA5 and MERRA-2) and find a detectable decrease in the ratio of MJO circulation to precipitation anomaly amplitude over the observational period, consistent with the change in dry static stability. MJO wind and precipitation anomalies individually increase in strength relative to the start of the record, but these changes are non-monotonic. These results suggest that weak-temperature-gradient theory may be able to help explain changes in MJO activity in recent decades.