Cyclic steps on ice. Journal of Geophysical Research
Cyclic steps on ice. Journal of Geophysical Research
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在冰上循环行走。
DOI：
10.1002/2015jf003736
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
Izumi N,(Greve6番目,他3人),
中科院分区：
文献类型：
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作者：
Yokokawa M;Izumi N,(Greve6番目,他3人),
边界波通常形成于冰和与其相邻流动的流体之间的界面，例如河流冰盖下的波纹，以及冰川上融水通道的河床上的台阶。它们也可能是由风形成的，比如南极冰盖上的巨型沙丘。火星极地冰帽上的螺旋槽被解释为由刮过冰的风形成的循环台阶。旋回台阶是上游迁移的反沙丘的近亲。冰上循环台阶的形成不仅是一个力学过程，也是一个热力学过程。关于冰上旋回台阶或上游迁移反沙丘形成的研究很少。在本研究中，我们进行了水槽实验，通过流水在冰上重现循环台阶，发现当弗劳德数大于1时，形成了台阶序列。这些台阶的特征使它们可以被确定为冲积河和基岩河中循环台阶的冰床类似物。我们进行了线性稳定性分析，并获得了上游迁移反沙丘形成的物理解释，即循环台阶的前体。我们将实验结果与分析的预测进行了比较，发现观察到的步骤落在分析预测界面不稳定性的范围内。我们还发现，短的反沙丘样起伏是形成明确台阶的前兆。这一事实表明，这种反沙丘样波动与分析预测的不稳定性相对应，是旋回阶跃的前兆。
Boundary waves often form at the interface between ice and fluid flowing adjacent to it, such as ripples under river ice covers, and steps on the bed of supraglacial meltwater channels. They may also be formed by wind, such as the megadunes on the Antarctic ice sheet. Spiral troughs on the polar ice caps of Mars have been interpreted to be cyclic steps formed by katabatic wind blowing over ice. Cyclic steps are relatives of upstream‐migrating antidunes. Cyclic step formation on ice is not only a mechanical but also a thermodynamic process. There have been very few studies on the formation of either cyclic steps or upstream‐migrating antidunes on ice. In this study, we performed flume experiments to reproduce cyclic steps on ice by flowing water, and found that trains of steps form when the Froude number is larger than unity. The features of those steps allow them to be identified as ice‐bed analogs of cyclic steps in alluvial and bedrock rivers. We performed a linear stability analysis and obtained a physical explanation of the formation of upstream‐migrating antidunes, i.e., precursors of cyclic steps. We compared the results of experiments with the predictions of the analysis and found the observed steps fall in the range where the analysis predicts interfacial instability. We also found that short antidune‐like undulations formed as a precursor to the appearance of well‐defined steps. This fact suggests that such antidune‐like undulations correspond to the instability predicted by the analysis and are precursors of cyclic steps.