Angular distribution models for top-of-atmosphere radiative flux estimation from the Clouds and the Earth's Radiant Energy System instrument on the Terra satellite.: Part II:: Validation

Errors in top- of- atmosphere ( TOA) radiative fluxes from the Clouds and the Earth's Radiant Energy System ( CERES) instrument due to uncertainties in radiance- to- flux conversion from CERES Terra angular distribution models ( ADMs) are evaluated through a series of consistency tests. These tests show that the overall bias in regional monthly mean shortwave ( SW) TOA flux is less than 0.2Wm(-2) and the regional RMS error ranges from 0.70 to 1.4 W m(-2). In contrast, SW TOA fluxes inferred using theoretical ADMs that assume clouds are plane parallel are overestimated by 3 - 4 W m(-2) and exhibit a strong latitudinal dependence. In the longwave ( LW), the bias error ranges from 0.2 to 0.4 W m(-2) and regional RMS errors remain smaller than 0.7 W m(-2). Global mean albedos derived from ADMs developed during the Earth Radiation Budget Experiment ( ERBE) and applied to CERES measurements show a systematic increase with viewing zenith angle of 4% - 8%, while albedos from the CERES Terra ADMs show a smaller increase of 1% - 2%. The LW fluxes from the ERBE ADMs show a systematic decrease with viewing zenith angle of 2% - 2.4%, whereas fluxes from the CERES Terra ADMs remain within 0.7% - 0.8% at all angles. Based on several months of multiangle CERES along- track data, the SW TOA flux consistency between nadir-and oblique- viewing zenith angles is generally 5% ( < 17 W m(-2)) over land and ocean and 9% ( 26 W m(-2)) in polar regions, and LW TOA flux consistency is approximate 3% ( 7 W m(-2)) over all surfaces. Based on these results and a theoretically derived conversion between TOA flux consistency and TOA flux error, the best estimate of the error in CERES TOA flux due to the radiance- to- flux conversion is 3% ( 10 W m(-2)) in the SW and 1.8% ( 3 - 5 W m(-2)) in the LW. Monthly mean TOA fluxes based on ERBE ADMs are larger than monthly mean TOA fluxes based on CERES Terra ADMs by 1.8 and 1.3 W m(-2) in the SW and LW, respectively.