A study of broadband parameterizations of the solar radiative interactions with water vapor and water drops

Three factors warrant considerable attention: 1) the manner in which the spectrally dependent drop single-scattering values are used to obtain the broadband cloud radiative properties, 2) the effect of the spectral attenuation by the vapor above the cloud on the determination of the broadband drop reflection and transmission, and 3) the broadband treatment of the spectrally dependent adsorption due to drops and vapor inside the cloud. The solar flux convergence in clouds is very sensitive to all these considerations. Ignoring effect 2 tends to overestimate the cloud heating, particularly for low clouds, while a poor treatment of effect 3 leads to an underestimate. A new parameterization that accounts for afforementioned considerations is accurate to within ~30% over a wide range of overcast sky conditions, including solar zenith angles and cloud characteristics (altitudes, drop models, optical depths, and geometrical thicknesses). -from Authors