Radiative Properties of Cirrus Clouds in the Infrared Region

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Abstract
A multiple-scattering radiative transfer model is employed to evaluate the 11 μm and the broad-band infrared (IR) fluxes, cooling rates and emittances in model cirrus clouds for a number of standard vertical atmospheric profiles of temperature and moisture. The single-scattering properties for scattering by mono- and polydispersed randomly orientated long ice columns and for the associated polydispersed equivalent spheres are used in the calculation. The results reveal IR reflectance at the cloud base of 4% (spheres) and 6% (cylinders). This reflectance modifies significantly the cloud effective emittances, cloud cooling rates and the emission by the total atmospheric column. It is shown that the radiative properties of model cirrus clouds determined under the equivalent sphere approximation represents well the properties determined for scattering by randomly orientated columns. The largest difference between the sphere and cylinder models is for reflectance which is a function of the degree of a... Abstract A multiple-scattering radiative transfer model is employed to evaluate the 11 μm and the broad-band infrared (IR) fluxes, cooling rates and emittances in model cirrus clouds for a number of standard vertical atmospheric profiles of temperature and moisture. The single-scattering properties for scattering by mono- and polydispersed randomly orientated long ice columns and for the associated polydispersed equivalent spheres are used in the calculation. The results reveal IR reflectance at the cloud base of 4% (spheres) and 6% (cylinders). This reflectance modifies significantly the cloud effective emittances, cloud cooling rates and the emission by the total atmospheric column. It is shown that the radiative properties of model cirrus clouds determined under the equivalent sphere approximation represents well the properties determined for scattering by randomly orientated columns. The largest difference between the sphere and cylinder models is for reflectance which is a function of the degree of a...

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