Tropical rainfall diurnal variation in a 20km-mesh atmospheric GCM

Tropical rainfall diurnal variation simulated by a super high resolution (about 20km-mesh) atmospheric general circulation model (MRI/JMA-TL959) is examined. Over continental and basin domain, the MRI/JMA-TL959 simulates observed rainfall diurnal variation in terms of peak time and a ratio of evening rain to morning rain. The model shows a few hours earlier peak rainfall than the observed. This feature is seen in the same model with lower (TL159 and TL95) horizontal resolution. Its very high horizontal resolution enables the MRI/JMA-TL959 to represent spatio-temporal characteristics of observed rainfall diurnal variation over the Indonesian Maritime Continent. Over Sumatra Island and the surrounding sea, for example, the MRI/JMA-TL959 simulates rainfall area migrating from the southwestern coastline toward inland in the daytime and toward offshore in the nighttime as seen in the observation. The speed of this rainfall migration is consistent with that of a gravity current. The model also seems to simulate local circulations such as land-sea breezes. We plan to investigate atmospheric circulations accompanied by rainfall diurnal cycle and dependency of ability to simulate observed rainfall diurnal cycle on horizontal resolution of topography and mountain height.