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首页> 外文期刊>Atmospheric chemistry and physics >Comprehensive tool for calculation of radiative fluxes: illustration of shortwave aerosol radiative effect sensitivities to the details in aerosol and underlying surface characteristics
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Comprehensive tool for calculation of radiative fluxes: illustration of shortwave aerosol radiative effect sensitivities to the details in aerosol and underlying surface characteristics

机译：计算辐射通量的综合工具：短波气溶胶辐射效应对气溶胶细节及其下层表面特性的敏感性说明

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The evaluation of aerosol radiative effect on broadband hemispherical solar flux is often performed using simplified spectral and directional scattering characteristics of atmospheric aerosol and underlying surface reflectance. In this study we present a rigorous yet fast computational tool that accurately accounts for detailed variability of both spectral and angular scattering properties of aerosol and surface reflectance in calculation of direct aerosol radiative effect. The tool is developed as part of the GRASP (Generalized Retrieval of Aerosol and Surface Properties) project. We use the tool to evaluate instantaneous and daily average radiative efficiencies (radiative effect per unit aerosol optical thickness) of several key atmospheric aerosol models over different surface types. We then examine the differences due to neglect of surface reflectance anisotropy, nonsphericity of aerosol particle shape and accounting only for aerosol angular scattering asymmetry instead of using full phase function. For example, it is shown that neglecting aerosol particle nonsphericity causes mainly overestimation of the aerosol cooling effect and that magnitude of this overestimate changes significantly as a function of solar zenith angle (SZA) if the asymmetry parameter is used instead of detailed phase function. It was also found that the nonspherical–spherical differences in the calculated aerosol radiative effect are not modified significantly if detailed BRDF (bidirectional reflectance distribution function) is used instead of Lambertian approximation of surface reflectance. Additionally, calculations show that usage of only angular scattering asymmetry, even for the case of spherical aerosols, modifies the dependence of instantaneous aerosol radiative effect on SZA. This effect can be canceled for daily average values, but only if sun reaches the zenith; otherwise a systematic bias remains. Since the daily average radiative effect is obtained by integration over a range of SZAs, the errors vary with latitude and season. In summary, the present analysis showed that use of simplified assumptions causes systematic biases, rather than random uncertainties, in calculation of both instantaneous and daily average aerosol radiative effect. Finally, we illustrate application of the rigorous aerosol radiative effect calculations performed as part of GRASP aerosol retrieval from real POLDER/PARASOL satellite observations.
机译：通常使用简化的大气气溶胶的光谱和方向散射特性以及下面的表面反射率来评估气溶胶辐射对宽带半球太阳通量的影响。在这项研究中，我们提出了一种严格而又快速的计算工具，该工具可准确地计算出直接气溶胶辐射效应时，气溶胶的光谱和角度散射特性以及表面反射率的详细变化。该工具是GRASP（气溶胶和表面特性的通用检索）项目的一部分。我们使用该工具评估不同表面类型上几个关键大气气溶胶模型的瞬时和每日平均辐射效率（每单位气溶胶光学厚度的辐射效应）。然后，我们检查由于忽略了表面反射率各向异性，气溶胶颗粒形状的非球形性而引起的差异，并且仅考虑了气溶胶角散射不对称而不是使用全相函数。例如，已表明，忽略气溶胶颗粒的非球形性主要是导致对气溶胶冷却效果的高估，如果使用不对称参数代替详细的相函数，则该高估的幅度将随着太阳天顶角（SZA）的变化而显着变化。还发现，如果使用详细的BRDF（双向反射率分布函数）代替表面反射率的朗伯近似，则在计算的气溶胶辐射效应中的非球面-球面差异不会显着改变。另外，计算表明，即使对于球形气雾剂，仅使用角散射不对称性也可以改变瞬时气雾剂辐射效应对SZA的依赖性。可以取消每日平均值的这种影响，但前提是太阳要达到顶峰。否则，仍然存在系统偏差。由于通过整合一系列SZA可获得每日平均辐射效应，因此误差随纬度和季节而变化。总而言之，本分析表明，在计算瞬时和每日平均气溶胶辐射效应时，使用简化的假设会导致系统的偏差，而不是随机的不确定性。最后，我们举例说明了严格的气溶胶辐射效应计算的应用，该计算是从真实POLDER / PARASOL卫星观测结果中获取GRASP气溶胶的一部分。

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