Tracking the MJO Eastward Propagation and Its Relationship with Dry Air Intrusion over the Equatorial Indian Ocean

The Madden-Julian Oscillation is the most prominent mode of variability on the time scale of weeks to months in the tropics. The canonical MJO is associated with a large-scale (e.g., thousands of km persisting >1 week) envelope of deep convection which initiates in the Indian Ocean and propagates eastward to the Indo-Pacific Maritime Continent (MC). The physical processes responsible for the eastward propagation of the MJO convection remains an active topic of research. Previous results based on three MJO events during the 2011-2012 CINDY/DYNAMO field campaign have suggested that dry air intrusion from the subtropics into the equatorial region associated with the Rossby-wave-like synoptic gyres can help reduce the convection on the west side of the MJO convective envelope, which is viewed as being more favorable for eastward propagation across the Indian Ocean. In this study, we examine the generality of these findings using large-scale precipitation tracking (LPT) to track MJO convective envelopes for October – April, 1998 – 2016 and identify events with dry-air intrusions. An empirical dry air intrusion index is developed to relate dry air intrusion on the west side of the envelope to eastward propagation. Then, the index is applied to a global model ensemble prediction of the November 2011 CINDY/DYNAMO event, to see whether the index distinguishes between relatively successful and unsuccessful MJO predictions. Preliminary results suggest that both too weak and too strong dry air intrusion is unfavorable for MJO eastward propagation.