Radiative transfer in cirrus clouds. Part IV: On cloud geometry, inhomogeneity, and absorption
- Univ. of Utah, Salt Lake City, UT (United States)
The effects of cloud geometry and inhomogeneity on the radiative properties of cirrus clouds are investigated by using the successive orders of scattering (SOS) approach for radiative transfer. This approach is an integral solution method that can be directly applied to specific geometry and inhomogeneous structure of a medium without the requirement of solving the basic differential radiative transfer equation. A specific interpolation scheme is developed for the intensity and source function iterations to reduce the computation effort. The SOS approach is shown to be particularly useful for cirrus clouds with optical depths less than about 5. Some demonstrative results show that the importance of the cloud-side scattering is dependent on the cloud horizontal dimension relative to the vertical thickness and that the cloud inhomogeneity can play a significant role in determining the domain-averaged solar reflection and transmission patterns. For finite clouds, the authors derive a physical equation using the Cartesian coordinates to define cloud absorption in terms of the absorbed solar flux per volume associated with the 3D flux divergence. The cloud absorption so defined in governed by the incident solar fluxes on three sides and reflection and transmission at the cloud top and bottom as well as radiation leakages out of the four sides. Using a solar wavelength of 2.22 {mu}m as an example, it is shown that anomalous cloud absorption can occur if specific cloud geometries are involved, for example, cubic clouds with an oblique solar zenith angle. Compatibilities between radiometric measurements from aircraft and theoretical calculations are further discussed. To resolve the anomalous cloud absorption issue from the physical perspective, it is essential that the cloud geometrical structure and cloud microphysics including aerosols be determined concurrently with radiometric measurements from the air. 38 refs., 11 figs., 3 tabs.
- DOE Contract Number:
- FG03-95ER61991
- OSTI ID:
- 443461
- Journal Information:
- Journal of the Atmospheric Sciences, Vol. 53, Issue 21; Other Information: PBD: 1 Nov 1996
- Country of Publication:
- United States
- Language:
- English
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