Radiative Transfer in Clouds with Internal Inhomogeniety
Abstract
In order to investigate the photon transport in inhomogeneous clouds, a Monte Carlo cloud model with internal variation of optical properties is developed. The data for cloud vertical internal inhomogeneity are chosen from published observations. Parameterization of the solar radiative properties of clouds is used in the form of the liquid water content and the effective radius of cloud droplet. The Monte Carlo simulations show that for overcast stratocumulus clouds, the differences in reflectance between the vertical inhomogeneous clouds and their planeparallel counterpart are very small (only about 1%). These differences can be enhanced up to 10% for large solar zenith angles, when the overcast clouds are separated into broken cloud fields. If the cloud coverage is large, the vertical inhomogeneity of clouds can cause about 7% increase in cloud absorption, which may help to explain the cloud absorption anomaly. Also, the parameterization of effective cloud amount for cloud absorption is discussed. For a vertical homogeneous planeparallel layer with horizontal cosinusoidal periodic variations of the extinction coefficient, the first order perturbation solution of the three dimensional radiative transfer equation has been obtained. There exists a correspondence between the distribution of the extinction coefficient and the distribution of the upwelling intensity. However, under certain conditions, the distribution of the upwelling intensity is opposite to the distribution of the extinction coefficient. If the solar zenith angle is large, shifts in the configurations of the distribution of the upwelling intensity may appear. The single scattering parameters can influence the distribution of the diffuse radiative intensity. The distribution of the heating rate inside the cloud and the distribution of the extinction coefficient are nearly coincident with each other. The perturbation solution can be extended to second order multimode case. The calculations show that the perturbation solution series is convergent. The cloud albedo changes from the unperturbed value when the second order perturbation correction is applied. The change of albedo can be negative as well as positive. The albedo changes due to the geometric factors and scattering factors are discussed. Also, the radiative transfer in a medium with an internal variation other than the cosinusoidal type is investigated. Monte Carlo simulation is used again to investigate the horizontal irradiance distribution in clouds, to verify the results of the analytical solution. Also the impact of geometric variation to the distribution of irradiance has been discussed.
 Publication:

Ph.D. Thesis
 Pub Date:
 1994
 Bibcode:
 1994PhDT.......263L
 Keywords:

 IRRADIANCE DISTRIBUTION;
 STRATOCUMULUS;
 Physics: Atmospheric Science