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首页> 外文期刊>Journal of Geophysical Research, D. Atmospheres: JGR >The impact of cloud vertical profile on liquid water path retrieval based on the bispectral method: A theoretical study based on large-eddy simulations of shallow marine boundary layer clouds
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The impact of cloud vertical profile on liquid water path retrieval based on the bispectral method: A theoretical study based on large-eddy simulations of shallow marine boundary layer clouds

机译：基于双谱法的云垂直剖面对液态水路径反演的影响：基于大涡模拟的浅海边界层云理论研究

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摘要

Passive optical retrievals of cloud liquid water path (LWP), like those implemented for Moderate Resolution Imaging Spectroradiometer (MODIS), rely on cloud vertical profile assumptions to relate optical thickness (τ) and effective radius (re) retrievals to LWP. These techniques typically assume that shallow clouds are vertically homogeneous; however, an adiabatic cloud model is plausibly more realistic for shallow marine boundary layer cloud regimes. In this study a satellite retrieval simulator is used to perform MODIS-like satellite retrievals, which in turn are compared directly to the large-eddy simulation (LES) output. This satellite simulator creates a framework for rigorous quantification of the impact that vertical profile features have on LWP retrievals, and it accomplishes this while also avoiding sources of bias present in previous observational studies. The cloud vertical profiles from the LES are often more complex than either of the two standard assumptions, and the favored assumption was found to be sensitive to cloud regime (cumuliform/stratiform). Confirming previous studies, drizzle and cloud top entrainment of dry air are identified as physical features that bias LWP retrievals away from adiabatic and toward homogeneous assumptions. The mean bias induced by drizzle-influenced profiles was shown to be on the order of 5–10 g/m~2. In contrast, the influence of cloud top entrainment was found to be smaller by about a factor of 2. A theoretical framework is developed to explain variability in LWP retrievals by introducingmodifications to the adiabatic re profile. In addition to analyzing bispectral retrievals, we also compare results with the vertical profile sensitivity of passive polarimetric retrieval techniques.
机译：像对中分辨率成像光谱仪（MODIS）实施的那样，对云液态水路径（LWP）的被动光学取回依赖于云垂直剖面假设来将光学厚度（τ）和有效半径（re）取回与LWP相关联。这些技术通常假定浅云在垂直方向上是同质的。然而，绝热云模型对于浅层海洋边界层云区域而言似乎更为现实。在这项研究中，卫星检索模拟器用于执行类似MODIS的卫星检索，然后将其直接与大涡流模拟（LES）输出进行比较。该卫星模拟器创建了一个框架，用于对垂直剖面特征对LWP取回的影响进行严格的量化，并做到了这一点，同时还避免了先前观测研究中存在的偏见。 LES的云垂直剖面通常比两个标准假设中的任何一个都更复杂，并且发现偏爱的假设对云区域（积云/层状）敏感。证实了先前的研究，细雨和云顶夹带的干燥空气被识别为使LWP取回偏离绝热和均质假设的物理特征。毛毛雨影响的轮廓引起的平均偏差显示为5-10 g / m〜2。相比之下，发现云顶夹带的影响较小，约为2倍。建立了一个理论框架以通过对绝热重剖面进行修改来解释LWP取回的可变性。除了分析双谱检索外，我们还将结果与无源极化检索技术的垂直剖面灵敏度进行比较。

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