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

这项工作的目的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。冰袋一直在移动，因为它很脆，所以会破裂。裂缝会裂开，形成断裂模式，并随着天气的变化而重组。在断裂处，冰群剪切，打开和闭合，并显示脊状隆起。此外，浮冰的变形遵循脆性材料常见的特殊关系。例如，裂缝的大小遵循这样一种关系，即裂缝的大小分布不随测量分辨率的变化而变化。这被称为尺度不变性。我们还看到了浮冰变形的其他紧急行为，在表面应力和海岸边界约束的影响下，浮冰表现为颗粒状或脆性塑料。我们将研究变形在哪个尺度上是尺度不变的，以及冰堆如何对风和冰盖的季节变化作出反应。我们的项目为这个问题带来的洞察力将导致气候和预测海冰漂移和变形模型的改进。这反过来将改善北极海上作业的风险评估和减灾工作。它还将允许对潜在的环境灾难（如可能无法控制的石油泄漏）做出反应的真实污染物扩散建模。我们的目的是解决关于海冰内部应力场是各向异性还是各向同性的争论，以及海冰是否在一系列尺度上表现出不同的塑性行为，确定在哪些尺度上变形是尺度不变的。我们将在覆盖北极盆地、天气尺度和亚中尺度（引线和裂缝的间距）的尺度上研究边界条件和强迫在限制海冰变形中的作用。根据在天气尺度和亚中尺度之间控制变形的物理机制转变的证据，我们将确定这与冰盖内裂缝的自组织如何相关。我们的假设是：大规模的变形是由冰群的几何形状和地表强迫、风和洋流控制的；变形分形尺度的明显转变与大尺度裂缝之间冰板的强迫和边界条件的变化有关；沿板块边界的应变减弱导致局部强迫和冰强度非均质性控制的尺度冰应力变小；随着充填体由封闭固结向松散粒状演化，变形尺度有季节性转变。测试这些假设将通过观测定向建模，使用一个离散元方法模型的机械行为的浮冰。连续模型的对照实验将验证特定的流变模型是否适用于各种尺度的海冰。我们期望识别具有海冰漂移、导通和海冰分散改进表征的模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.