Diurnal and MJO-scale variations in rain-rate in the Maritime Continent: Modelled and observed

Intraseasonal variability and the diurnal cycle have been shown to play a major role in modulating rain-rates over the land and sea in the Maritime Continent. Moreover, there is an interscale interaction between these two time-scales. Here, we present a 10-year climatology of modelled and observed rain-rates over the Maritime Continent in the Austral summer, using the WRF model with a horizontal grid spacing of 4 km, and satellite precipitation estimates TRMM 3B42 and CMORPH. Rain-rates and rain variability are aggregated on both MJO and diurnal scales.It is shown that despite an amplified diurnal cycle in the WRF model simulations relative to the satellite precipitation estimates, there is strong consistency between the model and satellite estimates in the timing and spatial variation in the average diurnal precipitation maximum. In general, the modelled average diurnal precipitation maximum leads the observed maximum by several hours, with largest differences on the slopes of the steepest topography.The diurnal precipitation cycle over the land has maximum amplitude 1-2 MJO phases ahead of the main convective envelope of the MJO in both the simulations and satellite estimates, with a weaker secondary maximum just after the main convective envelope. However, this variation in diurnal cycle with MJO phase is suppressed in the model relative to the satellite estimates, suggesting that forcing from the complex topography of the Maritime Continent is playing an over-active role in the model relative to large scale moisture variations. Over the land, the simulated rain-rates decrease rapidly after the afternoon peak, while the satellite estimates show a flatter curve or secondary evening peak, indicative of a transition to stratiform precipitation. This suggests deficiencies in the model's convective-stratiform transition in the tropics.