Project Title: Scale invariance of sea ice deformation: identifying how boundary conditions define the spatial ranges of these relationships (Award# 1740768)
PI:Hutchings, Jennifer K (firstname.lastname@example.org) Phone:(541) 737.4453 Institute/Department:Oregon State University, College of Earth, Ocean and Atmospheric Sciences IPY Project? Funding Agency:US\Federal\NSF\GEO\OPP\ARC\ANS Program Manager:Dr. Marc Stieglitz (email@example.com ) Discipline(s): |Oceanography |
Science Summary: 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. Researchers 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.
The aim of this project 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. Researchers 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, researchers will identify how this relates to self-organization of fractures within the ice pack. The PI’s 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.
Logistics Summary: Researchers have developed a model, Siku, optimized to simulate sea ice internal stress (pressured ice), sea ice dispersion and deformation, that will be further modified and tuned for our planned investigations. Satellite imagery and ice drift data will be used to test some hypotheses and constrain the model to test others. Unlike continuum models this model will use the discrete element method, with failure allowed for elements. This approach allows discrete phenomena such as cracks and leads to be resolved over multiple scales. Such a well-constrained model can then be used to identify realistic rheological sea ice models appropriate to scales resolved in forecast and climate models.
Analysis of observational data and model experiment will be combined in the investigations. No fieldwork will be conducted.
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