TY - JOUR

T1 - Effect of an orientation-dependent non-linear grain fluidity on bulk directional enhancement factors

AU - Rathmann, Nicholas M.

AU - Hvidberg, Christine S.

AU - Grinsted, Aslak

AU - Lilien, David A.

AU - Dahl-Jensen, Dorthe

PY - 2021/6/1

Y1 - 2021/6/1

N2 - Bulk directional enhancement factors are determined for axisymmetric (girdle and single-maximum) orientation fabrics using a transversely isotropic grain rheology with an orientation-dependent non-linear grain fluidity. Compared to grain fluidities that are simplified as orientation independent, we find that bulk strain-rate enhancements for intermediate-to-strong axisymmetric fabrics can be up to a factor of ten larger, assuming stress homogenization over the polycrystal scale. Our work thus extends previous results based on simple basal slip (Schmid) grain rheologies to the transversely isotropic rheology, which has implications for large-scale anisotropic ice-flow modelling that relies on a transversely isotropic grain rheology. In order to derive bulk enhancement factors for arbitrary evolving fabrics, we expand the c-axis distribution in terms of a spherical harmonic series, which allows the rheology-required structure tensors through order eight to easily be calculated and provides an alternative to current structure-tensor-based modelling.

AB - Bulk directional enhancement factors are determined for axisymmetric (girdle and single-maximum) orientation fabrics using a transversely isotropic grain rheology with an orientation-dependent non-linear grain fluidity. Compared to grain fluidities that are simplified as orientation independent, we find that bulk strain-rate enhancements for intermediate-to-strong axisymmetric fabrics can be up to a factor of ten larger, assuming stress homogenization over the polycrystal scale. Our work thus extends previous results based on simple basal slip (Schmid) grain rheologies to the transversely isotropic rheology, which has implications for large-scale anisotropic ice-flow modelling that relies on a transversely isotropic grain rheology. In order to derive bulk enhancement factors for arbitrary evolving fabrics, we expand the c-axis distribution in terms of a spherical harmonic series, which allows the rheology-required structure tensors through order eight to easily be calculated and provides an alternative to current structure-tensor-based modelling.

KW - Anisotropic ice

KW - ice rheology

KW - ice-sheet modelling

KW - COMPOSITE FLOW LAW

KW - DEEP ICE CORE

KW - ANISOTROPIC ICE

KW - POLYCRYSTALLINE ICE

KW - MODEL DEFORMATION

KW - POLAR ICE

KW - TEMPERATURE

KW - GREENLAND

KW - EVOLUTION

KW - RHEOLOGY

U2 - 10.1017/jog.2020.117

DO - 10.1017/jog.2020.117

M3 - Letter

VL - 67

SP - 569

EP - 575

JO - Journal of Glaciology

JF - Journal of Glaciology

SN - 0022-1430

IS - 263

ER -