1.3
Effects of clouds on direct radiative forcing by absorptive aerosols
William D. Collins, NCAR, Boulder, CO
We derive new global estimates of annual-mean shortwave absorption by carbonaceous aerosols under all-sky conditions. The objective is to calculate the absorption using cloud and aerosol data sets consistent with global satellite observations. The estimates are based upon two improvements relative to previous studies: cloud properties are obtained from the 3-hourly ISCCP data, and the aerosol distributions are produced by an aerosol assimilation model constrained by satellite retrievals. Our calculation is based upon a new, fast independent-column approximation (ICA) developed for the NCAR climate models. The estimates are computed for 1998 conditions. The clouds input to the ICA code are obtained from the 3-hourly global ISCCP data. The aerosols input to the ICA code are obtained from a global chemical transport model integrated using global NCEP meteorological analysis fields. The chemical model is adjusted by assimilation of satellite retrievals of aerosol optical depth. We obtain several estimates of the absorption assuming that the aerosols and cloud droplets are either internally or externally mixed. For the internal mixtures, the hydrophobic and elemental carbonaceous aerosols are treated as inclusions.
Session 1, Radiative Effects of Aerosols
Monday, 3 June 2002, 9:00 AM-11:45 AM
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