Short-wave optical properties of rain

The optical properties of rain were derived from Mie theory for the short-wave region 0.25—5 μm, using lognormal rain-drop size distributions. The optical depth of rain follows the large-drop approximation closely. The asymmetry parameter is slightly larger than that for typical clouds, especially at around 1.5 μm. The quite variable coalbedo was parameterized for 4 spectral bands as a function of the rain intensity. For a cloudlayer with rain, the suggested flexible parameterizations may be combined in a simple fashion with existing cloud-drop optics, e.g. in GCM radiation schemes.