Derivation of component aerosol direct radiative forcing at the top of atmosphere for clear-sky oceans

A two-step approach is proposed to derive component aerosol direct radiative forcing (ADRF) at the top of atmosphere (TOA) over global oceans from 60 degrees S to 60 degrees N for clear-sky condition by combining Terra CERES/MODIS-SSF shortwave (SW) flux and aerosol optical thickness (AOT) observations with the fractions of component AOTs from the GSFC/GOCART model. The derived global annual mean component ADRF is +0.08 +/- 0.17 W/m(2) for black carbon, -0.52 +/- 0.24 W/m(2) for organic carbon, -1.10 +/- 0.42 W/m(2) for sulfate, -0.99 +/- 0.37 W/m(2) for dust, -2.44 +/- 0.84 W/m(2) for sea salt, and -4.98 +/- 1.67 W/m(2) for total aerosols. The total ADRF has also been partitioned into anthropogenic and natural components with a value of -1.25 +/- 0.43 and -3.73 +/- 1.27 W/m(2), respectively. The major sources of error in the estimates have also been discussed. The analysis adds an alternative technique to narrow the large difference between current model-based and observation-based global estimates of component ADRF by combining the satellite measurement with the model simulation. (c) 2007 Elsevier Ltd. All rights reserved.