Monte-Carlo and Sparse Matrix Radiative Transfer Calculations on Multifractal Clouds: Flux Tubes and Singularities
Abstract
A current challenge of climate modeling is that general circulation model results are extremely sensitive to parameterizations of the poorly understood cloud/radiation interactions. In order to work out some fundamental problems occurring in radiative transfer in the atmosphere, one first needs a physically based model of cloud liquid water density which is able to yield realistic radiance multifractal variability over ranges spanning thousands of kilometers down to less than a meter. Indeed, analysis of nearly 1000 satellite and in situ cloud radiances has shown (in both infrared and visible wavelengths) that the radiances fields are highly multifractal on such huge ranges of scales. After discussing some technical points needed to obtain accurate li\-quid water density multifractal statistics, we then use both Monte-Carlo techniques as well as new (highly accurate, rapid) sparse matrix methods to simulate the radiative transfer in the cloud and relate scale by scale the resulting radiation fields and the scattering statistics to those of the cloud. Theoretically based on closure techniques, we have predicted that in multifractal clouds, the popular `independent pixel approximation' (IPA) should work except when applied to radiation flux tubes; and the latter are expected to be fractals. We directly test this hypothesis on the simulations.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSMNG23A..02G
- Keywords:
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- 0360 Transmission and scattering of radiation;
- 3210 Modeling;
- 3230 Numerical solutions;
- 3250 Fractals and multifractals;
- 3379 Turbulence