Long-wave optical properties of water clouds and rain

Mie theory is used for calculation of the long-wave (5–200 mm) optical properties of non-precipitating and precipitating water clouds, and of rain. The optical parameters (mass extinction and absorption coefficients, coalbedo and asymmetry parameter) are then parameterized as simple functions of cloud drop effective radius, cloud water amount and rain rate, for use in general circulation and weather forecast models. Broadband and some wideband parameterizations are given and tested both in two-stream and emissivity applications. A simple relation between the effective radius and cloud water content is also suggested for maritime and continental air masses.