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

Abstract

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 (N_d ). Absolute $\left(S_a=\frac{\partial A}{\partial N_d}\right)$ and relative $\left(S_r=\frac{\partial A}{\partial \ln \left(N_d\right)}\right)$ albedo susceptibilities are computed seasonally by exploiting the linear relationship between A and ln(N_d ) for shallow liquid clouds. Subtropical stratiform clouds (eastern Pacific, eastern Atlantic, and Australia) yield the highest S_r , followed by the extratropical oceans during their hemispheric summer. When S_r is cast in terms of F, the eastern Pacific clouds dominate S_r , with a secondary maximum offshore eastern Asia. S_a is mainly governed by N_d , with more pristine environments being more susceptible to change their albedo. While both S_a and S_r are advantageous for understanding radiative aspects of the aerosol indirect effect, S_r is more suitable for calculating changes in A and F due to the linear relationship between A and ln(N_d ).