Solar radiative line-by-line determination of water vapor absorption and water cloud extinction in inhomogeneous atmospheres

The "exact' solution of the radiative transfer equation for cloudy atmospheres with the cloud in a single model layer consumes an exorbitant amount of computational resources (~100hr on a Cyber 205). Two other techniques are based on the LBL spectral features of the H₂O molecule but consist of an approximation. The technique involving the "binning' of the vapor optical depths yields extremely accurate fluxes and heating rates for both the vapor and vapor-plus-cloud cases; in particular, it is a practical alternative for obtaining benchmark solutions to the solar radiative transfer in overcast atmospheres (3.8hr). In contrast, the multiple-scattering approximation technique does not yield precise results; however, considering its computational efficiency (0.5hr), it offers a rapid means to obtain a first-order approximation of the spectrally integrated quantities. -from Authors