Analysis of the role of Quasi-Biennial Oscillation on MJO eastward propagation through the Maritime Continent

One region particularly susceptible to enhanced convective activity during the Madden Julian Oscillation (MJO) active phase is the Maritime Continent (MC). As the ascending branch of the MJO envelope reaches the MC, the convective signal sometimes propagates eastward and reaches the Western Pacific Ocean (a propagating event). However, the convective envelope may also decouple from zonal wind anomalies and weaken over the MC, not reaching the Western Pacific Ocean (a non-propagating event). Propagation of the MJO across the MC is currently an active area of research.

In this study, anomalies of specific humidity, lower and upper tropospheric u and v wind components, and atmospheric temperature from the European Centre for Long-Range Weather Forecasts (ECMWF) ERA-Interim Reanalysis were compared for propagating and non-propagating MJO events. Of particular emphases were differences in the mean states of those variables for easterly, westerly and neutral QBO phases. Equatorial zonal wind anomalies over the Maritime Continent at 50 hPa were used to define QBO phase. The Wheeler-Hendon Realtime Multivariate (RMM) MJO Index was used to classify and categorize the geographic location (e.g. phase) and intensity (e.g. amplitude). The goal of this work was to better understand the physical mechanisms that favor MJO propagation across the MC.