Low‐cloud characteristics over the tropical western Pacific from ARM observations and CAM5 simulations
Low‐cloud characteristics over the tropical western Pacific from ARM observations and CAM5 simulations
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ARM 观测和 CAM5 模拟的热带西太平洋低云特征
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
Hsi‐Yen Ma
中科院分区：
文献类型：
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作者：
A. Chandra;Chidong Zhang;S. Klein;Hsi‐Yen Ma
这项研究评估了社区大气模式第5版(CAM5)再现热带西太平洋马努斯岛大气辐射测量(ARM)云雷达观测到的热带对流年份低云的能力。在这里，低云被定义为顶部低于冰冻水平，底部位于边界层内的云。对CAM5模拟和ARM观测中的低云统计进行了比较，包括它们的一般发生情况、平均垂直廓线、降水事件与非降水事件的比例、日循环和月时间序列。包括其他类型的云是为了在更广泛的背景下进行比较。比较表明，该模式高估了总云量及其降水量，但低估了总体上的低云量。然而，该模式在954到930 百帕之间的薄层中产生了过低的云，这与混合层顶部附近的过高湿度相吻合。这表明错误地产生过多的低云是由于云和湍流混合的参数化造成的。该模式也未能在低云中产生观测到的日循环，这不仅仅是因为模式粗略的网格间距没有解析马努斯岛。本研究论证了ARM长期热带西太平洋云观测在验证由全球气候模式模拟的低云方面的有效性，说明了在模式验证中使用ARM观测的问题，并提供了一个在热带西太平洋产生观测低云的严重模式偏差的例子。
This study evaluates the ability of the Community Atmospheric Model version 5 (CAM5) to reproduce low clouds observed by the Atmospheric Radiation Measurement (ARM) cloud radar at Manus Island of the tropical western Pacific during the Years of Tropical Convection. Here low clouds are defined as clouds with their tops below the freezing level and bases within the boundary layer. Low‐cloud statistics in CAM5 simulations and ARM observations are compared in terms of their general occurrence, mean vertical profiles, fraction of precipitating versus nonprecipitating events, diurnal cycle, and monthly time series. Other types of clouds are included to put the comparison in a broader context. The comparison shows that the model overproduces total clouds and their precipitation fraction but underestimates low clouds in general. The model, however, produces excessive low clouds in a thin layer between 954 and 930 hPa, which coincides with excessive humidity near the top of the mixed layer. This suggests that the erroneously excessive low clouds stem from parameterization of both cloud and turbulence mixing. The model also fails to produce the observed diurnal cycle in low clouds, not exclusively due to the model coarse grid spacing that does not resolve Manus Island. This study demonstrates the utility of ARM long‐term cloud observations in the tropical western Pacific in verifying low clouds simulated by global climate models, illustrates issues of using ARM observations in model validation, and provides an example of severe model biases in producing observed low clouds in the tropical western Pacific.