The role of droplet spectra for cloud radiative properties

The evolution of different types of clouds is simulated with a spectral scavenging and microphysics model, DESCAM, coupled to the dynamics of an ascending and entraining air‐parcel model. the resulting microphysical properties of the cloud are then coupled with a radiative‐transfer model in order to calculate the optical properties, the up‐ and downgoing radiative fluxes, the cloud optical depth, and the cloud albedo. For a stratiform cloud investigated during the North Atlantic Regional Experiment good agreement with the experimental data is obtained. For a medium‐sized convective cloud developing in marine or continental air the calculated cloud optical depth and the cloud albedo are compared with current parametrizations in global circulation models. the largest deviations are observed for cases with a large effective radius, e.g. when the cloud developed precipitation. In general, cloud optical depth and cloud albedo per unit cloud depth decrease with time, caused by the broadening of the cloud‐drop spectrum.