Three-dimensional Monte Carlo and diffusion radiative transfer models applied to inhomogeneous clouds and surfaces

This dissertation documents the development of the radiative transfer models for the application to 3D cloud and inhomogeneous terrain surfaces. A 3D Monte Carlo model for specific application to the broadband thermal radiative transfer has been developed in which the emissivities for gases and cloud particles are parameterized by using a single cubic element as the building block in 3D space. For spectral integration in the thermal infrared, the correlated k-distribution method has been used for the sorting of gaseous absorption lines in multiple-scattering atmospheres involving 3D clouds. The model is further applied to two real 3D cirrus cloud fields derived from satellite and millimeter cloud profiling radar to study the 3D cloud effects on radiative transfer.; The 3D diffusion radiative transfer equation, which utilizes a four-term spherical harmonics expansion for the scattering phase function and intensity, has been efficiently solved by using the full multigrid numerical method. This approach can simulate the transfer of solar and thermal infrared radiation in inhomogeneous cloudy conditions with different boundary conditions and sharp boundary discontinuity, and is well suited for radiation parameterization involving 3D and inhomogeneous clouds in climate models.; A 3D solar Monte Carlo radiative transfer model has been developed and applied to mountainous surfaces to study the diurnal, seasonal, and geographical variability in surface fluxes by choosing different solar zenith angles for one year period over a large scale mountain area. The characteristics of the flux components received by the terrain surfaces have been discussed. The difference between the incoming surface solar radiation for a flat surface with the same mean height as the mountain and those averaged over the domain have been used to investigate the significance of 3D topographical radiative transfer reference to the conventional radiation scheme used in general circulation models. The results reveal that the mountain effects on the surface fluxes have an order of 10 W/m2 difference compared with the flat surface.