Global estimates of changes in shortwave low-cloud albedo and fluxes due to variations in cloud droplet number concentration derived from CERES-MODIS satellite sensors.

15 years of Aqua CERES and MODIS observations are combined to derive nearly global maps of shortwave albedo (A) and flux (F) response to changes in cloud droplet number concentration (Nd ). Absolute ( S a = ∂ A ∂ N d ) and relative ( S r = ∂ A ∂ ln ( N d ) ) albedo susceptibilities are computed seasonally by exploiting the linear relationship between A and ln(Nd ) for shallow liquid clouds. Subtropical stratiform clouds (eastern Pacific, eastern Atlantic, and Australia) yield the highest Sr , followed by the extratropical oceans during their hemispheric summer. When Sr is cast in terms of F, the eastern Pacific clouds dominate Sr , with a secondary maximum offshore eastern Asia. Sa is mainly governed by Nd , with more pristine environments being more susceptible to change their albedo. While both Sa and Sr are advantageous for understanding radiative aspects of the aerosol indirect effect, Sr is more suitable for calculating changes in A and F due to the linear relationship between A and ln(Nd ).