Roles of land-surface properties and terrains on Maritime Continent rainfall and its seasonal evolution

Abstract

The Maritime Continent (MC) is characterized by a seasonal evolution of rainfall distinct from other regions, due to its unique land–sea distribution and topography. In this study, the roles of surface properties and terrains in controlling the regional climatological rainfall were investigated, based on general circulation model experiments. Results show that the existence of terrain can increase the MC land (MCL) rainfall mainly through its dynamical lifting effect, but otherwise has only moderate influence on rainfall over the MC ocean (MCO). On the other hand, the impact of MC land–sea distribution on the regional rainfall is more seasonally dependent. When replacing the MC flat-land with ocean, rainfall is significantly increased over both MCL and MCO during boreal summer-to-fall, but not in the winter-to-spring season. Further inspection showed that by eliminating the MC flat-land, there is enhanced atmospheric water vapor and convective instability in the summer-to-fall period, contributing to a dramatic increase in precipitation. On the other hand, changes in convective instability and atmospheric water vapor over the MCL act to counteract each other, leading to an only moderate change in rainfall during boreal winter-to-spring. The model-based results suggest that this seasonally dependent influence of the MC flat-land on regional climate mean rainfall is not determined by its modulation on the diurnal cycle. Our results also suggest a larger sensitivity of model bias in representing land–sea distribution/fraction over the MC region during the dry season (i.e. boreal summer) than in the wet season (i.e. boreal winter).