Samson M Hagos — Pacific Northwest National Laboratory
Zhe Feng — Pacific Northwest National Laboratory
Chuck N. Long — NOAA- Earth System Research Laboratory
Category
MJO: Madden-Julian Oscillation
Description
Precipitation (mm/day) (a) simulated by the WRF CSRM run at 3km grid spacing and (b) from TRMM 3B42 observation. The dashed line marks the longitude of the Island of Gan at which many of the AMIE/DYNAMO field campaign measurements were made.
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. Regional Cloud system resolving model (RCSRM) simulations and observations during the 2011 AMIE/DYNAMO field campaign over the Indian Ocean are used to study the moistening process. Shallow to deep transitions of individual cloud systems simulated by the RCSRM are identified and tracked and the spatial structure of relative humidity and hydrometeor concentration several hours before the transition are documented. Similar analysis is performed for the temporal evolution of these variables from the field campaign data. We show that moisture from falling, evaporating snow and ice particles of previous deep convection provide the mid-tropospheric moistening that leads to rapid shallow to deep transition. Successions of evaporative moistening and transitions to deep convection link MJO initiation and propagation to the Inter-tropical Convergence Zone.
Lead PI
Samson M Hagos — Pacific Northwest National Laboratory
