Sensitivity of Homogeneous Ice Nucleation to Aerosol Perturbations and Its Implications for Aerosol Indirect Effects Through Cirrus Clouds
Sensitivity of Homogeneous Ice Nucleation to Aerosol Perturbations and Its Implications for Aerosol Indirect Effects Through Cirrus Clouds
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DOI：
10.1002/2017gl076721
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发表时间：
2018-02
影响因子：
5.2
通讯作者：
X. Liu;X. Shi
中科院分区：
文献类型：
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作者：
X. Liu;X. Shi
人为气溶胶通过冰成核对卷云的影响的大小和迹象仍然非常不确定。本文基于云包模式的模拟，研究了气溶胶敏感性（ηα），定义为均匀冰成核形成的冰晶数浓度（Ni）对气溶胶数浓度（Na）的敏感性。该模型代表了均匀成核导致冰晶形成的基本过程。我们发现模型中气溶胶粒径分布的几何色散（σ）是影响ηα的关键因素。对于单分散尺寸分布，在典型卷云的垂直上升气流（V < 50 cm s−1）中ηα接近于零。然而，如果气溶胶颗粒在对流层上层遵循对数正态大小分布，σ为1.6-2.3，则ηα增加到0.1-0.3（即Na增加10倍，Ni增加1.3-2.0倍）。通过改变输入的气溶胶和环境参数，我们的模式再现了广泛用于全球气候模式（GCMs）的均匀冰核参数化的大范围ηα值。这些参数化的ηα的差异可以转化为通过卷云的人为气溶胶长波间接强迫的范围，从0.05到0.36 W m−2。我们的研究表明，较大的ηα(0.1-0.3)更合理，均匀成核参数化应包括真实的气溶胶大小分布，以准确量化人为气溶胶的间接影响。
The magnitude and sign of anthropogenic aerosol impacts on cirrus clouds through ice nucleation are still very uncertain. In this study, aerosol sensitivity (ηα), defined as the sensitivity of the number concentration (Ni) of ice crystals formed from homogeneous ice nucleation to aerosol number concentration (Na), is examined based on simulations from a cloud parcel model. The model represents the fundamental process of ice crystal formation that results from homogeneous nucleation. We find that the geometric dispersion (σ) of the aerosol size distribution used in the model is a key factor for ηα. For a monodisperse size distribution, ηα is close to zero in vertical updrafts (V < 50 cm s−1) typical of cirrus clouds. However, ηα increases to 0.1–0.3 (i.e., Ni increases by a factor of 1.3–2.0 for a tenfold increase in Na) if aerosol particles follow lognormal size distributions with a σ of 1.6–2.3 in the upper troposphere. By varying the input aerosol and environmental parameters, our model reproduces a large range of ηα values derived from homogeneous ice nucleation parameterizations widely used in global climate models (GCMs). The differences in ηα from these parameterizations can translate into a range of anthropogenic aerosol longwave indirect forcings through cirrus clouds from 0.05 to 0.36 W m−2 with a GCM. Our study suggests that a larger ηα (0.1–0.3) is more plausible and the homogeneous nucleation parameterizations should include a realistic aerosol size distribution to accurately quantify anthropogenic aerosol indirect effects.