Revisiting cloud overlap with a merged dataset of liquid and ice cloud extinction from CloudSat and CALIPSO

L. Oreopoulos, N. Cho, Dongmin Lee
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引用次数: 1

Abstract

We update the parameterization capturing the variation of parameters that describe how cloud occurrence (layer cloud fraction) and layer cloud optical depth (COD) distributions overlap vertically. Our updated analysis is motivated by the availability of a new dataset constructed by combining two products describing the two-dimensional extinction properties of liquid and ice phase clouds (and their mixtures) according to active cloud observations by the CloudSat and CALIPSO satellites. As before, cloud occurrence overlap is modeled with the decorrelation length of an inverse exponential function describing the decay with separation distance of the relative likelihood that two cloudy layers are overlapped maximally versus randomly. Similarly, cloud optical depth distribution vertical overlap is described again with a decorrelation length that describes the assumed inverse exponential decay with separation distance of the rank correlation between cloud optical depth distribution members in two cloudy layers. We derive the climatological zonal variability of these two decorrelation lengths using 4 years of observations for scenes of ∼100 km scale length, a typical grid size of numerical models used for climate simulations. As previously, we find a strong latitudinal dependence reflecting systematic differences in dominant cloud types with latitude, but substantially different magnitudes of decorrelation length compared to the previous work. The previously used parameterization form is therefore updated with new parameters to describe the latitudinal dependence of decorrelation lengths and its seasonal shift. Similar zonal patterns of decorrelation length are found when the analysis is broken down by different cloud classes. When the revised parameterization is implemented in a cloud subcolumn generator, simulated column cloud properties compare to observations quite well, and so do their associated cloud radiative effects, but improvements over the earlier version of the parameterization are marginal.
用CloudSat和CALIPSO合并的液体和冰云消光数据集重新审视云重叠
我们更新了参数化,捕捉描述云发生(层云分数)和层云光学深度(COD)分布如何垂直重叠的参数变化。根据CloudSat和CALIPSO卫星的活跃云观测,我们更新分析的动力来自于一个新数据集的可用性,该数据集结合了描述液态和冰相云(及其混合物)二维消光特性的两个产品。如前所述,云的发生重叠是用逆指数函数的去相关长度来建模的,该逆指数函数描述了两个云层最大重叠与随机重叠的相对可能性随分离距离的衰减。同样,云光学深度分布垂直重叠再次用去相关长度来描述,该去相关长度描述了两个云层中云光学深度分布成员之间的秩相关分离距离所假定的逆指数衰减。我们利用4年对~ 100公里尺度(用于气候模拟的数值模式的典型网格尺寸)的观测,推导出这两种去相关长度的气候纬向变异性。与以前一样,我们发现了强烈的纬度依赖性,反映了主导云类型随纬度的系统差异,但与以前的工作相比,去相关长度的大小有很大不同。因此,以前使用的参数化形式被更新为新的参数,以描述去相关长度的纬度依赖性及其季节变化。当分析被不同的云类分解时,发现了相似的去相关长度的纬向分布。当在云子柱生成器中实现修改后的参数化时,模拟柱云的属性与观测值的比较非常好,它们相关的云辐射效应也是如此,但与早期版本的参数化相比,改进是微不足道的。
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