Influence of crystal shapes on radiative fluxes in visible wavelength: ice crystals randomly oriented in space |
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| Authors: | P Chervet H Isaka T Nakajima |
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| Institution: | (1) Laboratoire de Météorologie Physique (URA 267/CNRS), 24 Avenue des Landais, 63177 Aubière Cedex, France;(2) Center for Climate System Research, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153, Japan;(3) Present address: Office National d\’Etudes et Recherches Aerospatiales, B.P. No. 72, 92322 Chatillon Cedex, France |
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| Abstract: | Radiative properties of cirrus clouds are one of the major unsolved problems in climate studies and global radiation budget. These clouds are generally composed of various ice-crystal shapes, so we tried to evaluate effects of the ice-crystal shape on radiative fluxes. We calculated radiative fluxes of cirrus clouds with a constant geometrical depth, composed of ice crystals with different shapes (hexagonal columns, bullets, bullet-rosettes), sizes and various concentrations. We considered ice particles randomly oriented in space (3D case) and their scattering phase functions were calculated by a ray-tracing method. We calculated radiative fluxes for cirrus layers for different microphysical characteristics by using a discrete-ordinate radiative code. Results showed that the foremost effect of the ice-crystal shape on radiative properties of cirrus clouds was that on the optical thickness, while the variation of the scattering phase function with the ice shape remained less than 3% for our computations. The ice-water content may be a better choice to parameterize the optical properties of cirrus, but the shape effect must be included. |
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