A global aerosol–climate model, including a two-moment cloud microphysical scheme and a parametrization for aerosol-induced ice formation in cirrus clouds, is applied in order to quantify the impact of aviation soot on natural cirrus clouds. Several sensitivity experiments are performed to assess the uncertainties in this effect related to (i) the assumptions on the ice nucleation abilities of aviation soot, (ii) the representation of vertical updrafts in the model, and (iii) the use of reanalysis data to relax the model dynamics (the so-called nudging technique). Based on the results of the model simulations, a radiative forcing from the aviation soot–cirrus effect in the range of −35 to 13 mW m⁻² is quantified, depending on the assumed critical saturation ratio for ice nucleation and active fraction of aviation soot but with a confidence level below 95 % in several cases. Simple idealized experiments with prescribed vertical velocities further show that the uncertainties on this aspect of the model dynamics are critical for the investigated effect and could potentially add a factor of about 2 of further uncertainty to the model estimates of the resulting radiative forcing. The use of the nudging technique to relax model dynamics is proved essential in order to identify a statistically significant signal from the model internal variability, while simulations performed in free-running mode and with prescribed sea-surface temperatures and sea-ice concentrations are shown to be unable to provide robust estimates of the investigated effect. A comparison with analogous model studies on the aviation soot–cirrus effect show a very large model diversity, with a conspicuous lack of consensus across the various estimates, which points to the need for more in-depth analyses on the roots of such discrepancies.

中文翻译：

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探索航空烟尘卷云效应的不确定性

应用全球气溶胶-气候模型，包括两时刻云微物理方案和卷云中气溶胶引起的冰形成的参数化，以量化航空烟尘对自然卷云的影响。进行了几个敏感性实验来评估这种影响的不确定性，这些不确定性与 (i) 对航空煤烟冰成核能力的假设，(ii) 模型中垂直上升气流的表示，以及 (iii) 使用再分析数据来确定放松模型动力学（所谓的轻推技术）。根据模型模拟的结果，来自航空烟尘卷云效应的辐射强迫在-35至13  mW m ^-2范围内是量化的，取决于冰核化的假设临界饱和比和航空煤烟的活性分数，但在一些情况下置信水平低于 95%。具有规定垂直速度的简单理想化实验进一步表明，模型动力学这方面的不确定性对于研究的影响至关重要，并且可能会给由此产生的辐射强迫的模型估计增加大约 2 倍的进一步不确定性。事实证明，使用微调技术来放松模型动力学对于从模型内部变化中识别出统计上显着的信号是必不可少的，而在自由运行模式下和规定的海面温度和海冰浓度下进行的模拟显示无法对调查的效果提供可靠的估计。