Sensitivity of aerosol radiative effect for VIS/NIR surface fluxes due to variations in relative humidity profiles

Accurate determination of global surface radiation budgets remains challenging due to complexities inherent in atmospheric Radiation Transfer Models (RTMs). This study utilizes the CCCma model, which is based on the correlated k-distribution method and evaluates its performance in accounting for aerosol effects on spectral surface fluxes. The CCCma RTM is verified by comparing its estimates of surface shortwave (SW) fluxes against high spectral resolution results from MODTRAN 6.0 and CERES SYN1deg products. Global annual mean surface SW fluxes are 246.5 W/m² for MODTRAN 6.0, 242.3 W/m² for CERES SYN1deg (Zhong et al., 2024), and 245.2 W/m² for CCCma. Although there are regional differences, they generally fall within CERES's estimated uncertainty of ~6 W/m² for monthly mean downwelling SW flux. Sensitivity analyses reveal that CCCma clear-sky SW fluxes are responsive to Precipitable Water Vapor (PWV) at approximately -0.7 W/m²/(kg/m²) over oceans, which is consistent with both MODTRAN 6.0 and CERES SYN1deg data. To quantify SW flux uncertainties, surface observations from seven diverse climatic regions were analyzed (see Brendecke et al. 2024). In this study, the CCCma RTM uncertainties will be further examined by varying relative humidity profiles. Furthermore, the impacts on CCCma simulated clear-sky VIS/NIR surface fluxes due to varying aerosol types (e.g. oceanic, rural, desert, and tropospheric) and relative humidity profiles will be reported.

References:

Brendecke, J., X. Dong, B. Xi, X. Zhong, J. Li, H.W. Barker and P. Pilewskie, 2024: Evaluation of Clear-Sky Surface Downward Shortwave Fluxes Computed by MODTRAN6.0, CKD, and CERES over different Climatic Regimes. Accepted by JQSRT.

Zhong, X., X. Dong, B, Xi, J. Brendecke, and P. Pilewskie, 2024: Tracing the physical signatures among the calculated global clear-sky spectral shortwave radiative flux distribution. Accepted by JQSRT.