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

这项工作的目标是确定控制波弗特海和楚科奇海冬季海冰变形的物理机制。海冰在风和洋流的影响下运动。冰块在不停地运动，由于它很脆，所以会破裂。裂缝裂开形成导线，形成断裂模式，随着天气的变化而重新组织。在断裂处，冰袋会剪切、打开和关闭，并显示出隆起。此外，堆积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的关系，即大小的分布不随测量的分辨率而改变。这称为标度不变性。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，冰表现为颗粒状或脆性塑性。我们将调查在哪些尺度上这种变形是尺度不变的，以及冰盖如何对风和冰盖的季节性变化做出反应。我们的项目给这个问题带来的洞察力将导致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。我们的目标是解决海冰内部应力场是各向异性还是各向同性的争论，以及海冰在一系列尺度上是否表现出不同的塑性行为，从而确定在哪些尺度上变形是尺度不变的。我们将研究边界条件和强迫在覆盖北极盆地的尺度、天气尺度和亚中尺度(引线和裂缝的间距)上限制海冰变形的作用。根据天气尺度和次中尺度之间控制变形的物理机制发生转变的证据，我们将确定这与冰盖内裂缝的自组织有何关系。我们的假设是：大尺度形变受控于冰包的几何形状和表面强迫、风和洋流；形变的分维标度的明显转变与定义较大尺度裂隙之间的冰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尺度的冰应力受力和冰强度的局部非均质性控制；随着冰包从约束和固结向无约束和粒状演化，形变的标度存在季节性转变。对这些假设的检验将通过观测指导的建模，使用堆积冰的力学行为的离散元方法模型。连续介质模型的控制对比实验将验证特定的流变模型是否适用于各种尺度的海冰。我们期望确定能够更好地代表海冰漂移、铅开口和海冰扩散的模型。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.