On the incident solar radiation in CMIP5 models

Abstract

Annual incident solar radiation at the top of atmosphere should be independent of longitudes. However, in many Coupled Model Intercomparison Project phase 5 (CMIP5) models, we find that the incident radiation exhibited zonal oscillations, with up to 30W/m 2 of spurious variations. This feature can affect the interpretation of regional climate and diurnal variation of CMIP5 results. This oscillation is also found in the Community Earth System Model. We show that this feature is caused by temporal sampling errors in the calculation of the solar zenith angle. The sampling error can cause zonal oscillations of surface clear-sky net shortwave radiation of about 3W/m 2 when an hourly radiation time step is used and 24W/m 2 when a 3h radiation time step is used. Key Points Spurious oscillation in insolation is found in CMIP5 model results The oscillation is attributed to sampling error in the solar zenith angle The spurious oscillation affects regional climate