Customization of RegCM3 Regional Climate Model for eastern Africa and a tropical Indian Ocean domain

Abstract

Rainfall is a driving factor of climate in the tropics and needs to be properly represented within a climate model. This study customizes the precipitation processes over the tropical regions of eastern Africa and the Indian Ocean using the International Centre for Theoretical Physics (ICTP) Regional Climate Model (RegCM3). The convective schemes of Grell with closures Arakawa-Schubert (Grell-AS)/Fritch-Chappel (Grell-FC) and Massachusetts Institute of Technology-Emanuel (MIT-EMAN) were compared to determine the most realistic spatial distribution of rainfall and partitioning of convective/stratiform rainfall when compared to observations from the Tropical Rainfall Measuring Mission (TRMM). Both Grell-AS and Grell-FC underpredicted convective rainfall rates over land, while over the ocean Grell-FC (Grell-AS) over- (under-) estimates convective rainfall. MIT-EMAN provides the most realistic pardoning and spatial distribution of convective rainfall despite the tendency for overestimating total rainfall. MIT-EMAN was used to further customize the subgrid explicit moisture scheme (SUBEX). Sensitivity tests were performed on the gridbox relative humidity threshold for cloudiness (RHmin) and the autoconversion scale factor (Cacs). An RHmin value of 60% (RHmin-60) reduced the amount of total rainfall over five heterogeneous rainfall regions in eastern Africa, with most of the reduction coming from the convective rainfall. Then, Cacs sensitivity tests improved upon the total rainfall amounts and convective stratiform partitioning compared to RHmin-60. Based upon all sensitivity simulations performed, the combination of the MIT-EMAN convective scheme, RHmin-60, and halving the model default value (0.4) of Cacs provided the most realistic simulation in terms of spatial distribution, convective partition, rainfall totals, and temperature bias when compared to observations. © 2009 American Meteorological Society.