Reconciling estimates for the first aerosol indirect forcing from satellites and models

Satellite-based estimates for the aerosol indirect forcing are consistently smaller than those from models due, in part, to the use of present-day results that do not capture the temporal changes between present day and pre-industrial conditions. We have previously used results from a coupled aerosol-climate model to pick regions and seasons that are sufficiently pristine to represent pre-industrial conditions. Then we used results from MODIS and CERES to estimate the forcing between present and pre-industrial conditions. The estimated range of forcing for the North Pacific Ocean region, -1.8 to -2.2 Wm-2, was similar to our modeled forcing for this region, -2.65 Wm-2. These forcings were limited to regions in which the cloud cover was greater than or equal to 50%. Here we use a cloud resolving model to explore whether this constraint can be relaxed to determine a forcing that includes regions with a smaller fraction of cloud cover.