Relationship Between Phase of the Quasi-Biennial Oscillation (QBO) and MJO Propagation Through the Maritime Continent

One region particularly favorable for 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, it 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 zonal (u) and meridional (v) wind components, geopotential height, and temperature from the European Centre for Long-Range Weather Forecasts (ECMWF) ERA-Interim Reanalysis were compared for propagating and non-propagating MJO events. 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). Of particular emphases were differences in the mean atmospheric states for easterly, westerly, and neutral QBO phases for different MJO propagating events. The goal of this work was to better understand the physical mechanisms that favor MJO propagation across the MC.