Abstract The nature of sidebranching in the facetted regions of snow crystals is investigated. It is shown that during the growth of a snow crystal, an initial sidebranch-pair forms after step bunching occurs on the leading prism planes, followed by step bunching on the adjacent flat basal face, producing a macrostep between the main branch and sidebranch feature. A Michelson interferometer–reflecting microscope setup was used to in-situ observe the three-dimensional morphology of a growing snow-crystal branch in a diffusion chamber. The macrostep on the basal plane was found to occur in the cases of simple facet growth, repetitive facet growth, and rounded tip growth, with the rounded tips forming at higher supersaturations. Thus, snow-crystal sidebranching involves a separation of the supply route of diffusing molecules on basal plane from the tip of the main-branch. Moreover, the sidebranches would fully sprout when the supersaturation increased, at which time the facetted branch tip abruptly narrowed and became rounded. These results indicate important roles of both the surface diffusion of water molecules and step migration for dendritic morphological instability on snow crystals.

中文翻译：

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雪晶生长过程中侧枝形成的三维方面

摘要 研究了雪晶刻面区域侧分支的性质。结果表明，在雪晶的生长过程中，先导棱镜平面上发生阶梯聚束后形成初始侧枝对，随后在相邻的平坦基面发生阶梯聚束，在主枝和侧枝特征之间产生宏观台阶。迈克尔逊干涉仪反射显微镜装置用于原位观察扩散室中生长的雪晶分支的三维形态。发现基面上的宏观台阶发生在简单小平面生长、重复小平面生长和圆形尖端生长的情况下，圆形尖端在较高的过饱和度下形成。因此，雪晶侧支涉及将基面上扩散分子的供应路线与主支的尖端分开。此外，当过饱和度增加时，侧枝会完全发芽，此时多面分支尖端突然变窄并变圆。这些结果表明水分子的表面扩散和阶梯迁移对雪晶上的树枝状形态不稳定性的重要作用。