Painemal, D; Minnis, P (2012). On the dependence of albedo on cloud microphysics over marine stratocumulus clouds regimes determined from Clouds and the Earth's Radiant Energy System (CERES) data. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 117, D06203.
The dependence of the top-of-the-atmosphere (TOA) albedo A on cloud microphysical properties was investigated for the three largest maritime stratocumulus clouds regimes: off California, Southeast Pacific (Chile-Peru), and southwest Africa (Namibia-Angola). Absolute S and relative S-R albedo susceptibilities to perturbations in cloud droplet number concentrations N-d, defined as dA/dN(d) and dA/dln(N-d) respectively, were calculated for the season having maximum cloud cover during the period 2006-2010. Satellite-based susceptibilities were computed by combining an adiabatically based N-d estimate and liquid water path (LWP) derived from Terra Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals matched with TOA A from the Clouds and the Earth's Radiant Energy System. Empirical susceptibility maps were calculated for three constant LWP intervals at 25, 50, and 90 g(-2). It was found that S increases with LWP, with small and spatially homogeneous values for low LWP, and a contrasting increase far offshore for larger LWP values. An overall increase of S-R with LWP was also observed, with larger values near the coast for LWP = 25 and 50 g(-2). A relatively homogeneous spatial pattern of maximum SR values covered most of each regime's domain for a LWP of 90 g(-2). These results highlight the importance of LWP in modulating the albedo susceptibility. The dependencies of S and S-R on LWP are mostly explained by variations in the mean Nd and cloud optical thickness (tau), with an increase of S with LWP linked to a decrease in Nd, whereas S-R increased with t and A, until reaching a maximum for A and t near 0.36-0.4 and 12-14 respectively, and decreasing thereafter, consistent with expectations based on two-stream estimates. Larger S-R values in the Southeast Pacific are thought to be the consequence of a drier and more pristine atmosphere. Radiative transfer simulations with realistic values of above-cloud water vapor path and aerosol optical thickness showed that differing atmospheric compositions could explain why the Chile-Peru regime was the marine stratocumulus cloud deck most susceptible to change its TOA albedo due to fractional changes in N-d.