The role of detrained moisture from ITCZ in the initiation of deep convection in Madden-Julian Oscillation

One of the unsolved mysteries of the Madden-Julian Oscillation (MJO) is the large-scale evolution from shallow to deep convection during its initiation over the Indian Ocean. While the ubiquitous shallow as well as congestus clouds gradually moisten the lower troposphere, the relatively rapid transition to deep convection suggests some other more effective mechanism of moistening the mid-troposphere might be in play. Using cloud system resolving model simulations and observations during the 2011 AMIE/DYNAMO field campaign over the Indian Ocean, we show that advection of moisture from falling, evaporating snow and ice particles of previous deep convection can provide this moistening. Successions of advective mid-tropospheric moistening and transitions to deep convection link the initiation of MJO to the Inter-tropical Convergence Zone.