• Arnott, W. P., Y. Dong, J. Hallet, and M. R. Poellot, 1994: Role of small ice crystals in radiative properties of cirrus: A case study, FIRE II, November 22, 1991. J. Geophys. Res.,99, 1371–1382.

  • Dowling, D. R., and F. L. Radke, 1990: A summary of the physical properties of cirrus clouds. J. Appl. Meteor.,29, 970–978.

  • Ebert, E. E., and J. A. Curry, 1992: A parameterization of ice cloud optical properties for climate models. J. Geophys. Res.,97, 3831–3836.

  • Foot, J. S., 1988: Some observations of the optical properties of clouds. Part II: Cirrus. Quart. J. Roy. Meteor. Soc.,114, 145–164.

  • Francis, P. N., A. Jones, R. W. Saunders, K. P. Shine, A. Slingo, and Z. Sun, 1994: An observational and theoretical study of the radiative properties of cirrus: Some results from ICE’89. Quart. J. Roy. Meteor. Soc.,120, 809–848.

  • Fu, Q., 1996: An accurate parameterization of the solar radiative properties of cirrus clouds for climate models. J. Climate,9, 2058–2082.

  • Gayet, J.-F., G. Fevbre, G. Brogniez, H. Chepfer, W. Renger, and P. Wendling, 1996: Microphysical and optical properties of cirrus and contrails: Cloud field study on 13 October 1989. J. Atmos. Sci.,53, 126–138.

  • Heymsfield, A. J., and C. M. R. Platt, 1984: A parameterization of the particle size spectrum of ice clouds in terms of the ambient temperature and ice water content. J. Atmos. Sci.,41, 846–855.

  • Liou, K. N., 1986: Influence of cirrus clouds on weather and climate processes: A global perspective. Mon. Wea. Rev.,114, 1167–1199.

  • ——, 1992: Radiation and Cloud Processes in the Atmosphere. Oxford University Press, 487 pp.

  • McFarlane, N. A., G. J. Boer, J.-P. Blanchet, and M. Lazare, 1992: The Canadien Climate Center second-generation general circulation model and its equilibrium climate. J. Climate,5, 1013–1044.

  • McFarquhar, G. M., and A. J. Heymsfield, 1996: Microphysical characteristics of three anvils sampled during the Central Equatorial Pacific Experiment. J. Atmos. Sci.,53, 2401–2423.

  • Mitchell, D. L., 1994: A model predicting the evolution of ice particle size spectra and radiative properties of cirrus clouds. Part I: Microphysics. J. Atmos. Sci.,51, 797–816.

  • Moss, S. J., P. N. Francis, and D. G. Johnson, 1996: Calculation and parameterization of the effective radius of ice particles using aircraft data. Proc. 12th Int. Conf. on Clouds and Precipitation, Zurich, Switzerland, Int. Commission on Clouds and Precipitation and Int. Assoc. of Meteorology and Atmospheric Science, 1255–1258.

  • Noone, K. B., K. J. Noone, J. Heintzenberg, J. Ström, and J. A. Ogren, 1993: In situ observations of cirrus cloud microphysical properties using the counterflow virtual impactor. J. Atmos. Oceanic Technol.,10, 294–303.

  • Ono, A., 1970: Growth mode of ice crystals in natural clouds. J. Atmos. Sci.,27, 649–658.

  • Ou, S.-C., and K. N. Liou, 1995: Ice microphysics and climatic temperature feedback. Atmos. Res.,35, 127–138.

  • ——, and Coauthors, 1995: Remote sounding of cirrus cloud optical depths and ice crystal sizes from AVHRR data: Verification using FIRE II IFO measurements. J. Atmos. Sci.,52, 4143–4158.

  • Platt, C. M. R., J. D. Spinhirne, and W. D. Hart, 1989: Optical and microphysical properties of a cold cirrus cloud: Evidence for regions of small ice particles. J. Geophys. Res.,94, 11 151–11 164.

  • Pruppacher, H. R., and J. D. Klett, 1978: Microphysics of Clouds and Precipitation. D. Reidel, 714 pp.

  • Ryan, B. F., 1996: On the global variation of precipitating layer clouds. Bull. Amer. Meteor. Soc.,77, 53–70.

  • Sassen, K., D. O. Starr, and T. Uttal, 1989: Mesoscale and microscale structure of cirrus clouds: Three case studies. J. Atmos. Sci.,46, 371–396.

  • Ström, J., B. Strauss, F. Schröder, T. Anderson, J. Heintzenberg, and P. Wendling, 1997: In situ observations of the microphysical properties of young cirrus clouds. J. Atmos. Sci.,54, 2542–2553.

  • Takano, Y., and K. N. Liou, 1989: Solar radiative transfer in cirrus clouds. Part I: Single-scattering and optical properties of hexagonal ice crystals. J. Atmos. Sci.,45, 3–19.

  • Zender, C. S., and J. T. Kiehl, 1994: Radiative sensitivities of tropical anvils to small ice crystals. J. Geophys. Res.,99, 25 869–25 880.

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The Effective Radius in Ice Clouds

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  • 1 Department of Meteorology, Stockholm University, Stockholm, Sweden
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Abstract

The effective radius (re) is a measure of the particle size used to calculate the optical properties of clouds. The objective of this study is to derive re from the microphysical composition of ice clouds. All ice crystals are assumed to be hexagonal columns with an aspect ratio depending on their size. Several existing particle size distributions are evaluated. The shape of the spectra is considered to be unsatisfactory for small particles and a new distribution is suggested that includes a Γ distribution for small crystals. The suggested spectrum agrees well with observations, although it is still speculative for small particles due to the limited availability of data.

The effective radius for nonspherical particles is not uniquely defined, and several possible definitions for re are tested. Large differences in re arise from the different definitions even if the same assumptions on the shape and the size distribution of ice particles are used. Norming factors help to adjust the differently defined re in order to make re from different sources compatible.

Finally, a new parameterization for re is suggested to avoid the expensive explicit computation. The proposed parameterization makes re a function of both the ice content and the temperature. A fair agreement between parameterized and observed re is found.

Corresponding author address: Dr. Klaus Wyser, Department of Meteorology, Stockholm University, S-106 91 Stockholm, Sweden.

Email: klaus@misu.su.se

Abstract

The effective radius (re) is a measure of the particle size used to calculate the optical properties of clouds. The objective of this study is to derive re from the microphysical composition of ice clouds. All ice crystals are assumed to be hexagonal columns with an aspect ratio depending on their size. Several existing particle size distributions are evaluated. The shape of the spectra is considered to be unsatisfactory for small particles and a new distribution is suggested that includes a Γ distribution for small crystals. The suggested spectrum agrees well with observations, although it is still speculative for small particles due to the limited availability of data.

The effective radius for nonspherical particles is not uniquely defined, and several possible definitions for re are tested. Large differences in re arise from the different definitions even if the same assumptions on the shape and the size distribution of ice particles are used. Norming factors help to adjust the differently defined re in order to make re from different sources compatible.

Finally, a new parameterization for re is suggested to avoid the expensive explicit computation. The proposed parameterization makes re a function of both the ice content and the temperature. A fair agreement between parameterized and observed re is found.

Corresponding author address: Dr. Klaus Wyser, Department of Meteorology, Stockholm University, S-106 91 Stockholm, Sweden.

Email: klaus@misu.su.se

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