Using sea-ice deformation fields to constrain the mechanical strength parameters of geophysical sea ice

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Description:	Tremblay, B Friday 15th September 2017 - 09:00 to 09:40


Created:	2017-09-18 13:06
Collection:	Mathematics of sea ice phenomena
Publisher:	Isaac Newton Institute
Copyright:	Tremblay, B
Language:	eng (English)


Abstract:	Co-author: Amelie Bouchat (McGill UniversityUsing sea-ice deformation fields to constrain the 2 mechanical strength parameters of geophysical sea ice) We investigate the ability of viscous-plastic (VP) sea-ice models with an elliptical yield curve and normal flow rule to reproduce the shear and divergence distributions derived from the RADARSAT Geophysical Processor System (RGPS). In particular, we reformulate the VP elliptical rheology to allow independent changes in the ice compressive, shear and isotropic tensile strength parameters (P, S, T* respectively) in order to study the sensitivity of the deformation distributions to changes in the ice mechanical strength parameters. Our 10-km VP simulation with standard ice mechanical strength parameters P∗= 27.5 kNm−2 , S∗ = 6.9 kNm−2, and T∗ = 0 kNm−2 (ellipse aspect ratio of e = 2) does not reproduce the large shear and divergence deformations observed in the RGPS deformation fields, and specifically lacks well-defined, active linear kinematic features (LKFs). Probability density functions (PDFs) for the shear and divergence of are nonetheless not Gaussian. Simulations with a reduced compressive or increased shear strength are in good agreement with RGPS-derived shear and divergence PDFs, with relatively more large deformations compared to small deformations. The isotropic tensile strength of sea ice on the other hand does not significantly affect the shear and divergence distributions. When considering additional metrics such as the ice drift error, mean ice thickness fields, and spatial scaling of the deformations, our results suggest that reducing the ice compressive strength is a better solution than increasing the shear strength when performing Arctic-wide simulations of the sea-ice cover with the VP elliptical rheology.

Abstract:

Co-author: Amelie Bouchat (McGill UniversityUsing sea-ice deformation fields to constrain the 2 mechanical strength parameters of geophysical sea ice)

We investigate the ability of viscous-plastic (VP) sea-ice models with an elliptical yield curve and normal flow rule to reproduce the shear and divergence distributions derived from the RADARSAT Geophysical Processor System (RGPS). In particular, we reformulate the VP elliptical rheology to allow independent changes in the ice compressive, shear and isotropic tensile strength parameters (P*, S*, T* respectively) in order to study the sensitivity of the deformation distributions to changes in the ice mechanical strength parameters. Our 10-km VP simulation with standard ice mechanical strength parameters P∗= 27.5 kNm−2 , S∗ = 6.9 kNm−2, and T∗ = 0 kNm−2 (ellipse aspect ratio of e = 2) does not reproduce the large shear and divergence deformations observed in the RGPS deformation fields, and specifically lacks well-defined, active linear kinematic features (LKFs). Probability density functions (PDFs) for the shear and divergence of are nonetheless not Gaussian. Simulations with a reduced compressive or increased shear strength are in good agreement with RGPS-derived shear and divergence PDFs, with relatively more large deformations compared to small deformations. The isotropic tensile strength of sea ice on the other hand does not significantly affect the shear and divergence distributions. When considering additional metrics such as the ice drift error, mean ice thickness fields, and spatial scaling of the deformations, our results suggest that reducing the ice compressive strength is a better solution than increasing the shear strength when performing Arctic-wide simulations of the sea-ice cover with the VP elliptical rheology.

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