The Role of Large-Scale Environment and Convective Diurnal Cycle in the Propagation of the MJO over the Maritime Continent

The Madden-Julian Oscillation (MJO), a large-scale disturbance of heavy rainfall that propagates eastward from the tropical Indian Ocean to the West Pacific on a timescale of 30-60 days, has profound impacts on downstream weather across the western hemisphere. About 50% of the time MJOs stall over the Maritime Continent (MC). Such a barrier effect of the MC on MJO is poorly represented in current weather and climate models, severely limiting their subseasonal-to-seasonal (S2S) forecast capabilities. We have analyzed satellite observations of sea surface temperature (SST), tropospheric temperature and moisture profiles, precipitation and cloud structure including diurnal cycle for a crossing MJO and a blocking MJO over the MC. Convection-permitting WRF simulations are conducted for both events. WRF simulations approximately capture the different propagation characteristics of the two events but with weaker amplitude in precipitation. We find that the crossing MJO is associated with warmer SST and higher water vapor over the open water in the MC than the blocking MJO, while the land surface temperature exhibits inhomogeneous mixed differences between the two events. Over the water, the crossing MJO is associated with much stronger diurnal variation of rainfall than the blocking MJO. Over the land, the diurnal variations are similar for both MJOs in observations, but the WRF model produces a noticeably stronger diurnal convection over the land during the blocking MJO than during the crossing MJO. Further analyses of the observations and model simulations are being conducted to understand the role of large-scale environment and convective diurnal cycle in the MJO propagation over the Maritime Continent.