Scale invariance of sea ice deformation: identifying how boundary conditions define the spatial ranges of these relationships

海冰变形的尺度不变性：确定边界条件如何定义这些关系的空间范围

• 批准号: 1740768
• 负责人: Jennifer Hutchings
• 金额: $ 46.97万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-04-15 至 2023-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1740768&HistoricalAwards=false
• 关键词: Scale; invariance; sea; ice; deformation

The goal of this work is to identify physical mechanisms controlling sea ice deformation in the winter Beaufort and Chukchi Seas. Sea ice moves under the influence of winds and ocean currents. The ice pack is in constant motion, and as it is brittle, cracks. Cracks open into leads, which form fracture patterns that reorganize with changes in the weather. At fractures, the ice pack shears, opens and closes, and displays ridging. Moreover, the pack ice deformation follow particular relationships common to brittle materials. For example, the size of fractures follow a relationship where the distribution of sizes do not change with the resolution they are measured over. This is termed scale invariance. We also see other emergent behavior of pack ice deformation, with the ice acting as a granular or brittle plastic under the influence of the surface stresses and coastal boundary constraints. We will investigate over which scales that deformation is scale invariant and how the ice pack responds to wind and seasonal changes in ice cover. The insight our project brings to this problem will result in improvements to modeling sea ice drift and deformation in climate and forecasting. This in turn will improve risk assessment and hazard mitigation for Arctic marine operations. It will also allow realistic contaminant dispersion modeling for response to potential environmental disasters such as an oil spill that could become uncontainable.Our aim is to settle a debate on whether the sea ice internal stress field is anisotropic or isotropic, and whether sea ice displays different plastic behavior over a range of scales, identifying over which scales that deformation is scale invariant. We will investigate the role of boundary conditions and forcing in confining sea ice deformation on scales covering the Arctic Basin, synoptic, and submeso- scale (the spacing of leads and cracks). Following evidence for a transition in the physical mechanism controlling deformation between the synoptic and sub-mesoscale, we will identify how this relates to self-organization of fractures within the ice pack. Our hypotheses are: large-scale deformation is controlled by geometry of the ice pack and surface forcing, winds and ocean currents; apparent transitions in the fractal scaling of deformation are related to changes in the forcing and boundary conditions defining plates of ice between the larger scale fractures; strain weakening along these plate boundaries result in smaller scale ice stress controlled by local heterogeneity in forcing and ice strength; and there is a seasonal transition in scaling of deformation as the pack evolves from confined and consolidated to unconfined and granular. Testing these hypotheses will be through observation directed modeling, using a discrete element method model of the mechanical behavior of pack ice. Controlled comparison experiments with continuum models will verify if particular rheological models are appropriate for sea ice across a variety of scales. We expect to identify models with improved representation of sea ice drift, lead opening and sea ice dispersion.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

这项工作的目标是确定控制冬季波弗特海和楚科奇海海冰变形的物理机制。海冰在风和洋流的影响下移动。冰袋不断运动，由于它很脆，所以会破裂。裂纹延伸至引线，形成断裂模式，并随着天气的变化而重组。在裂缝处，冰袋会剪切、打开和关闭，并出现隆起。此外，浮冰变形遵循脆性材料常见的特定关系。例如，裂缝的尺寸遵循这样的关系：尺寸的分布不随测量的分辨率而改变。这称为尺度不变性。我们还看到浮冰变形的其他新兴行为，冰在表面应力和沿海边界约束的影响下表现为颗粒状或脆性塑料。我们将研究变形在哪些尺度上是尺度不变的，以及冰袋如何响应风和冰盖的季节性变化。我们的项目对这个问题的见解将改进气候中海冰漂移和变形的建模和预测。这反过来将改善北极海洋作业的风险评估和减灾工作。它还将允许建立现实的污染物扩散模型，以应对潜在的环境灾难，例如可能变得无法控制的石油泄漏。我们的目的是解决关于海冰内应力场是各向异性还是各向同性的争论，以及海冰是否在一定范围内表现出不同的塑性行为，从而确定变形在哪些尺度上是尺度不变的。我们将研究边界条件和强迫在覆盖北极盆地、天气和亚细观尺度（引线和裂缝的间距）的尺度上限制海冰变形的作用。根据控制天气尺度和亚中尺度之间变形的物理机制转变的证据，我们将确定这与冰包内裂缝的自组织有何关系。我们的假设是：大规模变形是由冰袋的几何形状和表面强迫、风和洋流控制的；变形分形尺度的明显转变与定义较大尺度裂缝之间的冰板的强迫和边界条件的变化有关；沿这些板块边界的应变减弱导致较小规模的冰应力，受强迫和冰强度的局部不均匀性控制；随着堆积从受限和固结演变为无约束和粒状，变形规模会出现季节性转变。测试这些假设将通过观察定向建模，使用浮冰机械行为的离散元方法模型。使用连续模型的受控比较实验将验证特定的流变模型是否适用于各种尺度的海冰。我们希望找到能够更好地表现海冰漂移、引线开口和海冰扩散的模型。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。