Publication Abstracts

Mitchell et al. 1996

Mitchell, D.L., A. Macke, and Y. Liu, 1996: Modeling cirrus clouds. Part II: Treatment of radiative properties. J. Atmos. Sci., 53, 2967-2988, doi:10.1175/1520-0469(1996)053<2967:MCCPIT>2.0.CO;2.

A new radiation scheme, suitable for two stream radiative transfer models, was developed for cirrus clouds. Analytical expressions were derived for the extinction and absorption coefficients and the asymmetry parameter. These are functions of the ice particle size distribution parameters, ice particle shapes and wavelength. The ice particle shapes considered were hexagonal plates and columns, bullet rosettes and planar polycrystals. These appear to be the principle crystal types found in cirrus clouds. The formulation of radiative properties accounts for the size distribution projected area and the distance radiation travels through ice particles. For absorption, refraction and internal reflection of radiation were parameterized.

By assuming an idealized cirrus cloud, the dependence of the single scatter albedo, reflectance and emissivity on wavelength, ice particle shape and size distribution was demonstrated. Reflectance and emissivity were shown to vary by a factor of two or more due to differences in ice particle shape. Reflectance for hexagonal columns and plates were considerably lower than those for planar polycrystals and bullet rosettes.

The radiation scheme was tested with microphysical and radiation measurements from two cirrus cloud field studies. In both cases, radiative properties predicted from the observed microphysics were consistent with observed radiative properties. It was shown for both case studies that the radiation scheme could predict the observed mean ice particle size and ice water path (IWP) from the observed cloud albedo and emittance, provided the dominant ice particle shape was known or inferred. Retrieved IWP values differed from measurements derived values by ≤ 15% for the first case study and 18% on average for the second case study. Hence, it may be feasible to retrieve realistic IWP estimates from satellite data for a given ice particle shape.

Other radiation schemes have not been able to explain the second case study, which was characterized by relatively high albedos. Moreover, the physical explanation of these high albedos does not require asymmetry parameter values much different from those of cloud droplets.

The radiative properties were predicted from analytical expressions, making this scheme useful for predicting radiative properties in large scale models without excessive increase in computation time.

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BibTeX Citation

@article{mi00800v,
  author={Mitchell, D. L. and Macke, A. and Liu, Y.},
  title={Modeling cirrus clouds. Part II: Treatment of radiative properties},
  year={1996},
  journal={J. Atmos. Sci.},
  volume={53},
  pages={2967--2988},
  doi={10.1175/1520-0469(1996)053%3C2967%3AMCCPIT%3E2.0.CO;2},
}

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RIS Citation

TY  - JOUR
ID  - mi00800v
AU  - Mitchell, D. L.
AU  - Macke, A.
AU  - Liu, Y.
PY  - 1996
TI  - Modeling cirrus clouds. Part II: Treatment of radiative properties
JA  - J. Atmos. Sci.
VL  - 53
SP  - 2967
EP  - 2988
DO  - 10.1175/1520-0469(1996)053%3C2967%3AMCCPIT%3E2.0.CO;2
ER  -

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