Improvement Of The Cloud Optical Properties Parameterization And Its Application

A new ice cloud optical properties parameterization scheme with different assumptions of ice crystal shape is applied in the radiative transfer model and the climate model,and the effects in the radiative calculation and the climate modeling of the uncertainty in the ice-cloud optic are discussed in detail.The results show that the influences caused by ice crystal shape assumption on ice cloud optical depth,radiative fluxes,atmospheric heating rate and temperature are obvious.Compared with the spherical ice crystal assumption,the global average ice cloud optical depth decreases 0.28 and the most remarkable decrease is in the tropical area with the absolute value up to 1.02.Little changes are found in land areas in the middle and high latitudes.Global average upward longwave radiation flux at the TOA increases by 5.52W/m².Compared with observations,the multi-shape ice crystal assumption significantly reduces the underestimation by the spherical ice crystal assumption.The multi-shape ice crystal assumption weakens the shortwave radiation heating effect but enhances the longwave radiation cooling effect in the atmosphere,and these effects are particularly significant in the tropical upper troposphere.The change in the ice crystal shape has a significant effect on temperature,and temperature in the tropical upper troposphere decreases by more than 1.5 K.The weight of the habit also influences on the ice cloud optical properties and radiation.The results show that the influences of the ice crystal weight assumption chosen on the ice cloud longwave band-averaged volume extinction coefficient,the single scatter albedo and the asymmetry factor are obvious.The ice crystal weight assumption also has a significant influence on longwave radiative flux.It can cause up to-10.50W/m² of downward longwave radiative flux difference at the cloud base,and up to15.05W/m² of upward longwave radiative flux difference at the cloud top.The ice crystal weight assumption also has a significant influence on the shortwave radiative flux.It can cause up to 12.48W/m² of downward shortwave radiative flux difference at the cloud base,and up to-10.23W/m² of upward shortwave radiative flux difference at the cloud top.The assumption also has a great effect on the longwave heating rate,with 1.31K/d at the cloud top and-2.06K/d at the cloud base.Then,based on the improved ice cloud optical properties parameterization scheme,the effects of the HG?Henye-Greenstein?approximation on the shortwave ice-cloud radiation are analysed in details,which is widely used in radiative calculations.To the optical properties of the single ice crystal,the HG approximation causes large errors on 3^rd and 4^th coefficients of the Legendre expansion of the phase function,and the maximum values of the errors are-0.28 and-0.39 respectively,while the maximum values of the relative errors are-55.7%and-73.8%respectively.The errors of 4^th coefficients are higher than 3^rd coefficients,and the errors in near-infrared waves are higher than in visible waves.To the bulk optical properties of the ice clouds,the HG approximation causes large errors on 3^rd and 4^th coefficients,and the maximum values of the errors are-0.18 and-0.22 respectively,while the maximum values of the relative errors are-27.9%and-37.1%respectively.The errors of 4^th coefficients and in visible waves are higher,same to the single ice crystal.The maximum value of the errors on the downward shortwave flux is-2.78W/m²,and on the upward shortwave flux is-1.06W/m²,while on the shortwave heating rate is 0.27 K/d.The HG approximation underestimates the downward shortwave fluxes and overestimates the shortwave heating rates.Finally,the results show that the interaction of the gas absorption and the water cloud extinction can cause the decreasing of the shortwave heating rate and the shortwave net fluxes at the TOA.The former decreases 2.54W/m² in some areas,and the later decreases0.086K/d at some latitudes;after considering the effects of climate feedback,the former decreases 15.57W/m² in some areas,and the later decreases 0.107K/d at some latitudes.