Sensitivity Experiments of Rainfall to Warm Cloud Auto-Conversion Threshold and Relative Humidity Threshold of Cloudiness in RegCM4.6 over the Maritime Continent

Abstract

ABSTRACTIn the present work, sensitivity experiments for two parameter schemes are conducted using the Regional Climate Model System, version 4.6, to improve the model capability for reproducing rainfall over the Maritime Continent (MC). One parameter is the warm cloud auto-conversion threshold in the Emanuel convective scheme, and the other parameter is the relative humidity threshold of cloudiness in the subgrid explicit moisture microphysics scheme. Our results show that using the optimized values of these two parameters can reduce the rainfall bias over land in the western MC. In addition, we also show that the choice of the sea surface temperature forcing data is important in improving the model's performance. The improvement is confirmed from extreme year simulations and the long-run simulation in both spatial and temporal characteristics. The optimized simulation shows improved model performance in both wet and dry seasons. The underestimation of the annual and interannual rainfall variability is alleviated in the optimized simulation. This indicates the model's ability to reproduce the MC's rainfall under the appropriate parameterization schemes. We expect that our optimized parameterization can be used to reproduce more reliable downscaled rainfall data to support various climate research activities over the MC.