Simulation of the diurnal variation of rainfall over the western Maritime Continent using a regional climate model

This study evaluates the performance of the MIT regional climate model (MRCM) in simulating the temporal and spatial structure of the diurnal variation of rainfall over the western Maritime Continent. In order to investigate the effect of model resolution, two identical simulations with 27 and 12 km horizontal resolutions are performed for a 30-year period (1982-2011). The simulated climatological features are compared with the TRMM 3B42 3-h observations. The analysis is focused on the regional characteristics of diurnal variation of rainfall in terms of phase and amplitude, with an emphasis on the difference in behaviors between land and ocean. Systematic modulation of the diurnal cycle over land and ocean characterizes the rainfall pattern over the Maritime Continent. The evening peak with strong amplitude over land and the morning peak with weak amplitude over ocean reflect the contrast in behavior between land and ocean. In general, both simulations are able to capture major features of diurnal rainfall variations with similarity in several aspects to TRMM observation. However, the improvement from increasing resolution is more apparent in the coastal and offshore areas, where rainfall processes are strongly tied with low-level wind that varies diurnally and regionally. A more realistic coastline and a sharp gradient of elevation derived from high resolution boundary conditions enhance the local circulation associated with land-sea breeze and topographic complexity, which in turn induces a favorable condition for the offshore convergence and associated rainfall occurrence. The MRCM with 12 km resolution simulates propagation of rainfall from inland to coastal or offshore areas, such as in the vicinity of western Sumatra, northern Java, and western Borneo Islands. However, further improvements can be gained from even higher resolution models, such as convection-permitting scale.