PNNL

Abstract

Understanding the variations in the strength of Madden-Julian Oscillation (MJO) events as they propagate across the Indo-Pacific Maritime Continent (MC) has been an unmet challenge. Moisture fluxes estimated directly from precipitation show a slow eastward propagation of zonal moisture flux convergence between the Asian and Australian monsoon convergence centers from summer to winter. As individual MJO events propagate across this zonally and seasonally varying monsoonal moisture convergence, their strengths also vary. Specifically, MJO events starting in February, March and April tend to be weak over the eastern Indian Ocean but they strengthen as they propagate into the moisture convergence region over the western Pacific. During May, June and July, the moisture convergence pattern is reversed and MJO events weaken as they propagate into moisture divergence region in the western Pacific. Winter MJO events are most likely to be strong over the MC region, particularly when the Australian monsoon is strong.