Radiation Profiles in Extended Water Clouds. I: Theory

A detailed multiple-scattering model has been employed to investigate the sensitivity of radiation profiles and flux divergences to changes in macrostructure and microstructure of basic water cloud types. The study has been performed on a range of cloud types including variable distributions of liquid water content (LWC) and drop-size distributions. Total shortwave heating rates vary from 1 to 5°C h−1 and are larger in higher clouds. IR cooling rates in the upper regions of cloud also increase with increasing elevation and are dominated by the atmospheric window contribution. Thus the typical instrument discriminating the IR radiation between 7 and 14,μm will measure almost the entire IR radiative cooling or heating of low-level water clouds. Both shortwave heating and IR cooling within cloud layers are primarily dependent on LWC and its vertical distribution and are more or less independent of drop-size distribution. Cloud albedo does vary with drop-size distribution but is virtually independent of LWC distribution for fixed total water.