Measurement-based estimation of aerosol radiative forcing: The spatial mean and the spatial gradient of radiative forcing

This paper presents a measurement-based estimation of aerosol direct radiative forcing and aerosol indirect radiative forcing, and their spatial heterogeneity. Unlike anthropogenic greenhouse gases (GHG), aerosols have much greater spatial heterogeneity in their radiative forcing. This forcing can cause and/or modulate mesoscale and large-scale circulations, thus altering the regional climate. In order to represent this potential impact, we diagnose the Normalized Gradient of Radiative Forcing (NGoRF), as a fraction of the present global heterogeneous insolation attributed to human activity. Although the GHG have a larger forcing as measured in terms of a spatial mean top of the atmosphere (TOA) value, the aerosol direct and indirect effects have far greater NGoRF values than that of GHG. Thus, they have a greater potential to modulate atmospheric circulations and consequently regional climate.