Sensitivities study of sulfate radiative properties and direct radiative forcing with LASG IAP AGCM

The sulfate radiative properties and its direct radiative forcing (DRF) are investigated in a recent version of AGCM developed by LASG/IAP/CAS. A scheme well representing sulfate hygroscopic growth is used to examine the sulfate DRF in our study. The results indicate the global annual mean sulfate DRF in all-sky and its normalized value are -0.57 watt square meter and -166 watt each mg. respectively, which is comparable to the range presented in IPCC AR4. The sulfate DRF is very sensitive to simulated relative humidity (RH) in lower troposphere. The inclusion of re-analysis humidity can partly improve sulfate DRF simulations over the regions with large humidity biases, but the improper performance of sulfate aerosol optical depth and DRF over Eurasia continent is still closely involved in RH and cloud processes in AGCM. Our study suggests that the study of sulfate radiative properties and DRF, should be conducted in a great depth in current AGCM to further reduce their uncertainty.