The Geometry of Rimed Aggregate Snowflakes: A Modeling Study
The Geometry of Rimed Aggregate Snowflakes: A Modeling Study
复制标题
边缘聚集雪花的几何形状：建模研究
DOI：
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发表时间：
2019
影响因子：
6.8
通讯作者：
S. Kneifel
中科院分区：
文献类型：
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作者：
A. Seifert;J. Leinonen;C. Siewert;S. Kneifel
本文利用计算机模拟冰晶的聚集和成霜过程，研究成霜聚集雪花的几何形状。由于聚集体几何形状的普遍性，当以适当的归一化变量进行公式化时，转化为类似于谷粒的颗粒是自相似的，并且与聚集体的特定性质无关。因此，初级晶体的颗粒习性，聚集体的大小或雾凇质量的密度，不会导致结构的变化，在过渡到<$球。因此，这种过渡可以通过相似性方法使用许多单独的镶边聚集体的模拟来参数化。这些参数化可以取代许多云模型中使用的经典填充模型。在一维拉格朗日超粒子模型中应用和测试参数化，以模拟液体层中聚集体的生长。我们发现，相似性模型的几何形状的有边雪花导致更快的增长，由riming，因此，增加的沉淀率相比，填充模型。其主要原因是相似模型适当地考虑了在结霜早期阶段最大尺寸的增加，而填充模型则忽略了这一点。
Computer simulations of the aggregation and riming of ice crystals are performed to investigate the geometry of rimed aggregate snowflakes. Due to the universality of the geometry of aggregates, the conversion to a graupel‐like particle is self‐similar and independent from specific properties of the aggregate, when formulated in properly normalized variables. Hence, the particle habit of the primary crystals, the size of the aggregate or the density of the rime mass, does not lead to a structural change in the transition to graupel. Therefore, this transition can be parameterized by a similarity approach using simulations of many individual rimed aggregates. These parameterizations can replace the classic fill‐in model used in many cloud models. The parameterizations are applied and tested in a one‐dimensional Lagrangian superparticle model to simulate the growth of aggregates in a liquid layer. We find that the similarity model for the geometry of rimed snowflakes leads to a more rapid growth by riming and, hence, an increased precipitation rate compared to the fill‐in model. The main reason for this is that the increase of the maximum dimension during the early stages of riming is properly taken into account by the similarity model, whereas it is neglected by the fill‐in model.