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3D Delta-Diffusion and IR Monte-Carlo Methods for Radiative Transfer Applied to Inhomogeneous Cirrus over the ARM-SGP Site

Chen, Y.(a), Liou, K.N.(a), Gu, Y.(a), Ou, S.C.(a), and Mace, G.G.(b), University of California, Los Angeles (a), University of Utah (b)
Fourteenth Atmospheric Radiation Measurement (ARM) Science Team Meeting

An efficient method based on a full multigrid approach has been developed to solve the 3D delta-diffusion radiative transfer equation, which utilizes four-term spherical harmonics expansion for the phase function and intensity. This method first solves the inhomogeneous partial differential equation on a number of coarse grids and subsequently performs interpolation to predivided fine grids to speed up the convergence of the solution, particularly useful for cloud radiation parameterization in numerical models. We also developed a 3D Monte-Carlo model for specific application to the broadband IR radiative transfer in which the emissivities for gases and cloud particles are parameterized in a single cubic element. For spectral integration, the correlated k-distribution method is used to incorporate the gaseous absorption in multiple-scattering atmospheres involving 3D clouds. Comparison of the broadband results computed from these two methods with those from existing models and the pixel-by-pixel approximation shows reasonable agreement. We apply these 3D radiative transfer models to the 3D cirrus cloud fields derived from remote sensing on the basis of a unification of satellite and ground-based cloud profiling radar observations over the ARM-SGP site. Two cases, which illustrate substantial horizontal and vertical variability in ice crystal size distribution, have been chosen: April 18, 1997 and March 9, 2000. The constructed 3D ice water content and mean effective size are compared to the results analyzed from the available in situ aircraft data. 3D heating and cooling rates of these cirrus clouds in terms of variability in different spatial scales and mean values computed from the 3D radiative transfer models will be presented and physically discussed.

Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).