Radiation budget in RegCM4: simulation results from two radiative schemes over the South West Indian Ocean

Abstract

One way to estimate solar resources required by the solar industry is via regional climate models (RCMs), which provide a comprehensive and physically based state-of-the-art description of the atmosphere and its interactions with the Earth's surface. Here we describe the first application of RCM simulations with Regional Climate Model Version 4 (RegCM4) for radiation fluxes over the South West Indian Ocean (SWIO). We analyzed the performance of RegCM4 on radiation fluxes, especially its radiative schemes presentation, which could provide basic information for surface solar radiation temporal-spatial variability analysis with RegCM4 over SWIO region. We used ERA-Interim reanalysis data for the period 2000-2005 to drive RegCM4 to simulate the radiation budget and associated parameters such as cloud cover, precipitation and surface temperature, over Southern Africa and the SWIO with a horizontal resolution of 50 km. The 2 existing available radiation schemes were tested and evaluated: (1) the default radiation scheme of the NCAR Community Climate Model Version 3 (CCM); and (2) the recently implemented Rapid Radiation Transfer Model (RRTM). To analyze the behavior of the radiation schemes and their impact on the surface climate, model outputs were validated against available satellite and reanalysis data. A comparison of the seasonal radiation budget as simulated by RegCM4-CCM and RegCM4-RRTM at the surface and at the top of the atmosphere showed good qualitative agreement. RegCM4 with the RRTM scheme generally better simulates the radiation budget and cloud cover over the whole domain with regard to the reference data than RegCM4 with the CCM scheme; RRTM could therefore be chosen as the radiative scheme in subsequent studies of surface solar radiation by RegCM4.