Daehyun Kim

Propagating vs. Non-propagating Madden-Julian Oscillation


Associated with the Madden-Julian oscillation (MJO), the planetary-scale convective 
anomaly over the Indian Ocean (IO) usually propagates eastward and reach the west 
Pacific (WP), but not always. The role of dryness over the Maritime continent (MC) and 
the WP on the propagation of the anomalous convection over the IO is investigated. 
When the convective anomaly reaches the eastern IO, dry conditions prevail over the MC 
and the WP. The strength of the dryness is not tightly coupled to the strength of the 
convective anomaly over the eastern IO, but exhibits a large variability over the events. 
All 99 MJO onset events over the eastern IO are classified into three categories based on 
the strength of the dry anomaly over the MC and the WP. We found that the IO 
convection anomaly lives longer, and makes a further propagation when the dry anomaly 
is relatively stronger. When the dry anomaly is relatively weaker, the convection anomaly 
ceases before reach the WP in most cases. The dry anomaly plays a dynamically active 
role on the propagation of the IO convection through the Rossby response to it, which 
enhances low-tropospheric easterly anomaly to the east of the convection anomaly. The 
enhanced easterly anomaly helps the propagation of the IO convection by inducing a 
stronger moisture convergence in the lower troposphere and the boundary layer to the 
east of the convection.