Secondary ice production via rime-splintering is considered to be an important process for rapid glaciation and high ice crystal numbers observed in mixed-phase convective clouds. An open question is how rime-splintering is triggered in the relatively short time between cloud formation and observations of high ice crystal numbers. We use idealised simulations of a deep convective cloud system to investigate the thermodynamic and cloud microphysical evolution of air parcels, in which the model predicts secondary ice formation. The Lagrangian analysis suggests that the “in-situ” formation of rimers either by growth of primary ice or rain freezing does not play a major role in triggering secondary ice formation. Instead, rimers are predominantly imported into air parcels through sedimentation form higher altitudes. While ice nucleating particles (INPs) initiating heterogeneous freezing of cloud droplets at temperatures warmer than $-10$ ${}^{\circ }\mathrm{C}$ have no discernible impact of the occurrence of secondary ice formation, in a scenario with rain freezing secondary ice production is initiated slightly earlier in the cloud evolution and at slightly different places, although with no major impact on the abundance or spatial distribution of secondary ice in the cloud as a whole. These results suggest that for interpreting and analysing observational data and model experiments regarding cloud glaciation and ice formation it is vital to consider the complex vertical coupling of cloud microphysical processes in deep convective clouds via three-dimensional transport and sedimentation.

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理想深对流中的次生冰形成-主要冰的来源及其对冰川的影响

人们认为，通过冰e裂片进行次生冰是快速冰川化和在混合相对流云中观察到的高冰晶数的重要过程。一个悬而未决的问题是，在云层形成和高冰晶数观测之间的相对较短的时间内，如何触发霜裂。我们使用深对流云系统的理想化模拟来研究空气包裹的热力学和云微物理演化，其中模型预测了二次冰的形成。拉格朗日分析表明，无论是初生冰的生长还是雨水冻结的“原地”形成，在触发次生冰的形成中都没有主要作用。取而代之的是，边缘矿主要是通过更高海拔的沉淀作用而进入空气包裹的。 $-10$ ${}^{\circ }\mathrm{C}$ 对次生冰的形成没有明显影响，在降雨冻结的情况下，次生冰的产生在云层演化的早期以及在稍微不同的地方开始，尽管对次生冰的丰度或空间分布没有重大影响。整个云。这些结果表明，对于解释和分析有关云层冰川和冰层形成的观测数据和模型实验，至关重要的是考虑通过对流层云的三维运移和沉降，云层微物理过程在垂直对流中的复杂垂直耦合。