Abstract
Parametrization of radiation transfer through clouds is an important factor in the ability of Numerical Weather Prediction models to correctly describe the weather evolution. Here we present a practical parameterization of both liquid droplets and ice optical properties in the longwave and shortwave radiation. An advanced spectral averaging method is used to calculate the extinction coefficient, single scattering albedo, forward scattered fraction and asymmetry factor (βext, ϖ, f, g), taking into account the nonlinear effects of light attenuation in the spectral averaging. An ensemble of particle size distributions was used for the ice optical properties calculations, which enables the effective size range to be extended up to 570 μm and thus be applicable for larger hydrometeor categories such as snow, graupel, and rain. The new parameterization was applied both in the COSMO limited-area model and in ICON global model and was evaluated by using the COSMO model to simulate stratiform ice and water clouds. Numerical weather prediction models usually determine the asymmetry factor as a function of effective size. For the first time in an operational numerical weather prediction (NWP) model, the asymmetry factor is parametrized as a function of aspect ratio. The method is generalized and is available on-line to be readily applied to any optical properties dataset and spectral intervals of a wide range of radiation transfer models and applications.
Highlights
Clouds have the main influence on the radiative fluxes in the atmosphere and on the entire atmospheric energy budget
Yang et al (2000) [7] published their work on the single scattering optical properties of six ice crystals habits that are usually found in in situ measurements and spectral bands in the range 0.2 μm–5 μm. They used geometric optics method (GOM) and finite-difference time-domain (FDTD) to calculate the extinction and absorption coefficients, and the asymmetry factor and forward peak of the phase function, which were parameterized as a function of effective size
Thousands of generalized gamma distributions were assumed to simulate a broad range of ice clouds
Summary
Clouds have the main influence on the radiative fluxes in the atmosphere and on the entire atmospheric energy budget. Yang et al (2000) [7] published their work on the single scattering optical properties of six ice crystals habits that are usually found in in situ measurements (plate, columns, hollow column, planar and spatial bullet rosettes, and aggregates) and spectral bands in the range 0.2 μm–5 μm They used GOM and FDTD to calculate the extinction and absorption coefficients, and the asymmetry factor and forward peak of the phase function (the latter is only significant for short wave intervals), which were parameterized as a function of effective size. In their study, they fitted the diameter of equivalent area DA and the diameter of equivalent volume Dv in terms of the maximum dimension Dmax for each crystal shape where the Dmax/Deff ratio depends on the ice particle habit. As the main goal of this work was to implement an efficient, simple, and fast scheme for NWP and CLM models, the single-particle data by Fu (1996) [15] and Fu et al (1998) [17] was chosen as the base of our parametrizations for ice optical properties
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
