Arctic low clouds and the water they contain influence the evolution of the Arctic system through their effects on radiative fluxes, boundary layer mixing, stability, turbulence, humidity, and precipitation. Atmospheric models struggle to accurately simulate the occurrence and properties of Arctic low clouds, stemming from errors in both the simulated atmospheric state and the dependence of cloud properties on the atmospheric state. Knowledge of the contributions from these two factors to the model errors allows for the isolation of the process contributions to the model–observation differences. We analyze the differences between the Arctic System Reanalysis version 2 (ASR) and data taken during the September 2014 Arctic Radiation–IceBridge Sea and Ice Experiment (ARISE) airborne campaign conducted over the Beaufort Sea. The results show that ASR produces less total and liquid cloud water than observed along the flight track and is unable to simulate observed large in-cloud water content. Contributing to this bias, ASR is warmer by nearly 1.5 K and drier by 0.06 g kg⁻¹ (relative humidity 4.3 % lower) than observed. Moreover, ASR produces cloud water over a much narrower range of thermodynamic conditions than shown in ARISE observations. Analyzing the ARISE–ASR differences by thermodynamic conditions, our results indicate that the differences are primarily attributed to disagreements in the cloud–thermodynamic relationships and secondarily (but importantly) to differences in the occurrence frequency of thermodynamic regimes. The ratio of the factors is about $\mathrm{2}/\mathrm{3}$ to $\mathrm{1}/\mathrm{3}$. Substantial sampling uncertainties are found within low-likelihood atmospheric regimes; sampling noise cannot be ruled out as a cause of observation–model differences, despite large differences. Thus, an important lesson from this analysis is that when comparing in situ airborne data and model output, one should not restrict the comparison to flight-track-only model output.

中文翻译：

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使用 ARISE 机载原位观测评估北极系统再分析波弗特海低云中模拟的云液态水

北极低云及其所含的水通过对辐射通量、边界层混合、稳定性、湍流、湿度和降水的影响来影响北极系统的演变。大气模型难以准确模拟北极低云的发生和特性，这是由于模拟的大气状态和云特性对大气状态的依赖性造成的误差。了解这两个因素对模型误差的贡献可以隔离过程对模型观察差异的贡献。我们分析了北极系统再分析第 2 版 (ASR) 与 2014 年 9 月在波弗特海上空进行的北极辐射-冰桥海冰实验 (ARISE) 空中活动期间获取的数据之间的差异。结果表明，ASR 产生的总和液态云水比沿飞行轨迹观察到的要少，并且无法模拟观察到的大量云中水含量。造成这种偏差的原因是 ASR 的温度升高了近 1.5 K，干燥了 0.06 g kg ^-1（相对湿度低 4.3 %）比观察到的。此外，ASR 在比 ARISE 观测中显示的热力学条件范围更窄的范围内产生云水。通过热力学条件分析 ARISE-ASR 差异，我们的结果表明，这些差异主要归因于云-热力学关系的分歧，其次（但重要的是）归因于热力学状态发生频率的差异。因子的比值约为$\mathrm{2}/\mathrm{3}$ 到 $\mathrm{1}/\mathrm{3}$. 在低可能性的大气状态中发现了大量的采样不确定性；尽管存在很大差异，但不能排除采样噪声作为观察模型差异的原因。因此，从这一分析中得到的一个重要教训是，在比较现场机载数据和模型输出时，不应将比较限制为仅飞行轨迹模型输出。