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Elizabeth C. Hunke - One of the best experts on this subject based on the ideXlab platform.

  • On the Consistent Scaling of Terms in the Sea-Ice Dynamics Equation
    Journal of Physical Oceanography, 2004
    Co-Authors: William M. Connolley, Elizabeth C. Hunke, Jonathan M. Gregory, A. J. Mclaren
    Abstract:

    The standard way in which the Sea-Ice Dynamics equation is used in models assumes that the wind stress and ocean drag do not depend on the Sea-Ice concentration. It is demonstrated that this assumption is inconsistent with the free-drift limit, and how great an effect it has in practIce is examined. By examining the momentum balance in the free-drift limit, the authors determine the proper area scaling for the forcing terms, thereby obtaining a more accurate solution, particularly in low-Ice-concentration regions.

  • the elastic viscous plastic Sea Ice Dynamics model in general orthogonal curvilinear coordinates on a sphere incorporation of metric terms
    Monthly Weather Review, 2002
    Co-Authors: Elizabeth C. Hunke, John K. Dukowicz
    Abstract:

    Abstract A new discretization for the elastic–viscous–plastic (EVP) Sea Ice Dynamics model incorporates metric terms to account for grid curvature effects in curvilinear coordinate systems. A fundamental property of the viscous–plastic Ice rheology that is invariant under changes of coordinate system is utilized; namely, the work done by internal forces, to derive an energy dissipative discretization of the divergence of the stress tensor that includes metric terms. Comparisons of simulations using an older EVP numerical model with the new formulation highlight the effect of the metric terms, which can be significant when Ice deformation is allowed to affect the Ice strength.

  • The Elastic Viscous Plastic Sea Ice Dynamics Model in General Orthogonal Curvilinear Coordinates on a Sphere—Incorporation of Metric Terms
    Monthly Weather Review, 2002
    Co-Authors: Elizabeth C. Hunke, John K. Dukowicz
    Abstract:

    Abstract A new discretization for the elastic–viscous–plastic (EVP) Sea Ice Dynamics model incorporates metric terms to account for grid curvature effects in curvilinear coordinate systems. A fundamental property of the viscous–plastic Ice rheology that is invariant under changes of coordinate system is utilized; namely, the work done by internal forces, to derive an energy dissipative discretization of the divergence of the stress tensor that includes metric terms. Comparisons of simulations using an older EVP numerical model with the new formulation highlight the effect of the metric terms, which can be significant when Ice deformation is allowed to affect the Ice strength.

  • viscous plastic Sea Ice Dynamics with the evp model linearization issues
    Journal of Computational Physics, 2001
    Co-Authors: Elizabeth C. Hunke
    Abstract:

    Abstract Behavior of the elastic–viscous–plastic (EVP) model for Sea Ice Dynamics is explored, with particular attention to a necessary numerical linearization of the internal Ice stress term in the momentum equation. Improvements to both the mathematical and numerical formulations of the model have moderated the impact of linearizing the stress term; simulations with the original EVP formulation and the improved version are used to explain the consequences of using different numerical approaches. In particular, we discuss the model behavior in two regimes, low Ice concentration such as occurs in the marginal Ice zone, and very high Ice concentration, where the Ice is nearly rigid. Most of these results are highly relevant to the viscous–plastic (VP) Ice Dynamics model on which the EVP model is based. We provide examples of certain pathologies that the VP model and its numerical formulations exhibit at steady state.

  • Viscous–Plastic Sea Ice Dynamics with the EVP Model: Linearization Issues
    Journal of Computational Physics, 2001
    Co-Authors: Elizabeth C. Hunke
    Abstract:

    Abstract Behavior of the elastic–viscous–plastic (EVP) model for Sea Ice Dynamics is explored, with particular attention to a necessary numerical linearization of the internal Ice stress term in the momentum equation. Improvements to both the mathematical and numerical formulations of the model have moderated the impact of linearizing the stress term; simulations with the original EVP formulation and the improved version are used to explain the consequences of using different numerical approaches. In particular, we discuss the model behavior in two regimes, low Ice concentration such as occurs in the marginal Ice zone, and very high Ice concentration, where the Ice is nearly rigid. Most of these results are highly relevant to the viscous–plastic (VP) Ice Dynamics model on which the EVP model is based. We provide examples of certain pathologies that the VP model and its numerical formulations exhibit at steady state.

John K. Dukowicz - One of the best experts on this subject based on the ideXlab platform.

  • the elastic viscous plastic Sea Ice Dynamics model in general orthogonal curvilinear coordinates on a sphere incorporation of metric terms
    Monthly Weather Review, 2002
    Co-Authors: Elizabeth C. Hunke, John K. Dukowicz
    Abstract:

    Abstract A new discretization for the elastic–viscous–plastic (EVP) Sea Ice Dynamics model incorporates metric terms to account for grid curvature effects in curvilinear coordinate systems. A fundamental property of the viscous–plastic Ice rheology that is invariant under changes of coordinate system is utilized; namely, the work done by internal forces, to derive an energy dissipative discretization of the divergence of the stress tensor that includes metric terms. Comparisons of simulations using an older EVP numerical model with the new formulation highlight the effect of the metric terms, which can be significant when Ice deformation is allowed to affect the Ice strength.

  • The Elastic Viscous Plastic Sea Ice Dynamics Model in General Orthogonal Curvilinear Coordinates on a Sphere—Incorporation of Metric Terms
    Monthly Weather Review, 2002
    Co-Authors: Elizabeth C. Hunke, John K. Dukowicz
    Abstract:

    Abstract A new discretization for the elastic–viscous–plastic (EVP) Sea Ice Dynamics model incorporates metric terms to account for grid curvature effects in curvilinear coordinate systems. A fundamental property of the viscous–plastic Ice rheology that is invariant under changes of coordinate system is utilized; namely, the work done by internal forces, to derive an energy dissipative discretization of the divergence of the stress tensor that includes metric terms. Comparisons of simulations using an older EVP numerical model with the new formulation highlight the effect of the metric terms, which can be significant when Ice deformation is allowed to affect the Ice strength.

  • An Elastic–Viscous–Plastic Model for Sea Ice Dynamics
    Journal of Physical Oceanography, 1997
    Co-Authors: Elizabeth C. Hunke, John K. Dukowicz
    Abstract:

    The standard model for Sea Ice Dynamics treats the Ice pack as a visco‐plastic material that flows plastically under typical stress conditions but behaves as a linear viscous fluid where strain rates are small and the Ice becomes nearly rigid. Because of large viscosities in these regions, implicit numerical methods are necessary for time steps larger than a few seconds. Current solution methods for these equations use iterative relaxation methods, which are time consuming, scale poorly with mesh resolution, and are not well adapted to parallel computation. To remedy this, the authors developed and tested two separate methods. First, by demonstrating that the viscous‐plastic rheology can be represented by a symmetric, negative definite matrix operator, the much faster and better behaved preconditioned conjugate gradient method was implemented. Second, realizing that only the response of the Ice on timescales associated with wind forcing need be accurately resolved, the model was modified so that it reduces to the viscous‐plastic model at these timescales, whereas at shorter timescales the adjustment process takes place by a numerically more efficient elastic wave mechanism. This modification leads to a fully explicit numerical scheme that further improves the model’s computational efficiency and is a great advantage for implementations on parallel machines. Furthermore, it is observed that the standard viscous‐plastic model has poor dynamic response to forcing on a daily timescale, given the standard time step (1 day) used by the Ice modeling community. In contrast, the explicit discretization of the elastic wave mechanism allows the elastic‐viscous‐plastic model to capture the Ice response to variations in the imposed stress more accurately. Thus, the elastic‐viscous‐plastic model provides more accurate results for shorter timescales associated with physical forcing, reproduces viscous‐plastic model behavior on longer timescales, and is computationally more efficient overall.

  • an elastic viscous plastic model for Sea Ice Dynamics
    Journal of Physical Oceanography, 1997
    Co-Authors: Elizabeth C. Hunke, John K. Dukowicz
    Abstract:

    The standard model for Sea Ice Dynamics treats the Ice pack as a visco‐plastic material that flows plastically under typical stress conditions but behaves as a linear viscous fluid where strain rates are small and the Ice becomes nearly rigid. Because of large viscosities in these regions, implicit numerical methods are necessary for time steps larger than a few seconds. Current solution methods for these equations use iterative relaxation methods, which are time consuming, scale poorly with mesh resolution, and are not well adapted to parallel computation. To remedy this, the authors developed and tested two separate methods. First, by demonstrating that the viscous‐plastic rheology can be represented by a symmetric, negative definite matrix operator, the much faster and better behaved preconditioned conjugate gradient method was implemented. Second, realizing that only the response of the Ice on timescales associated with wind forcing need be accurately resolved, the model was modified so that it reduces to the viscous‐plastic model at these timescales, whereas at shorter timescales the adjustment process takes place by a numerically more efficient elastic wave mechanism. This modification leads to a fully explicit numerical scheme that further improves the model’s computational efficiency and is a great advantage for implementations on parallel machines. Furthermore, it is observed that the standard viscous‐plastic model has poor dynamic response to forcing on a daily timescale, given the standard time step (1 day) used by the Ice modeling community. In contrast, the explicit discretization of the elastic wave mechanism allows the elastic‐viscous‐plastic model to capture the Ice response to variations in the imposed stress more accurately. Thus, the elastic‐viscous‐plastic model provides more accurate results for shorter timescales associated with physical forcing, reproduces viscous‐plastic model behavior on longer timescales, and is computationally more efficient overall.

  • An elastic-viscous-plastic model for Sea Ice Dynamics
    1996
    Co-Authors: Elizabeth C. Hunke, John K. Dukowicz
    Abstract:

    The standard model for Sea Ice Dynamics treats the Ice pack as a viscous-plastic material that flows plastically under typical stress conditions but behaves as a linear viscous fluid where strain rates are small and the Ice becomes nearly rigid. Because of large viscosities in these regions, implicit numerical methods are necessary for timesteps larger than a few seconds. Current solution methods for these equations use iterative relaxation methods, which are time consuming, scale poorly with mesh resolution, and are not well adapted to parallel computation. To remedy this, we have developed and tested two separate methods. First, by demonstrating that the viscous-plastic rheology can be represented by a symmetric, negative definite matrix operator, we have implemented the faster and better behaved preconditioned conjugate gradient method. Second, realizing that only the response of the Ice on time scales associated with wind forcing need be accurately resolved, we have modified the model to reduce to the viscous-plastic model at these time scales; at shorter time scales the adjustment process takes place by a numerically efficient elastic wave mechanism. This modification leads to a fully explicit numerical scheme which further improves the computational efficiency and is an advantage for implementations on parallel machines. Furthermore, we observe that the standard viscous-plastic model has poor dynamic response to forcing on a daily time scale, given the standard time step (1 day) used by the Ice modeling community. In contrast, the explicit discretization of the elastic wave mechanism allows the elastic-viscous-plastic model to capture the Ice response to variations in the imposed stress more accurately. Thus, the elastic-viscous-plastic model provides more accurate results for shorter time scales associated with physical forcing, reproduces viscous-plastic model behavior on longer time scales, and is computationally more efficient. 49 refs., 13 figs., 6 tabs.

Benjamin Smith - One of the best experts on this subject based on the ideXlab platform.

  • the interplay of recent vegetation and Sea Ice Dynamics results from a regional earth system model over the arctic
    Geophysical Research Letters, 2020
    Co-Authors: Wenxin Zhang, Ralf Döscher, Torben Koenigk, Paul A. Miller, Christer Jansson, Patrick Samuelsson, Benjamin Smith
    Abstract:

    Recent accelerated warming over the Arctic coincides with Sea Ice reduction and shifting patterns of land cover. We use a state-of-the-art regional Earth system model, RCAO-GUESS, which comprises a dynamic vegetation model (LPJ-GUESS), a regional atmosphere model (RCA), and an ocean Sea Ice model (RCO), to explore the dynamic coupling between vegetation and Sea Ice during 1989–2011. Our results show that RCAO-GUESS captures recent trends in observed Sea Ice concentration and extent, with the inclusion of vegetation Dynamics resulting in larger, more realistic variations in summer and autumn than the model that does not account for vegetation Dynamics. Vegetation feedbacks induce concomitant changes in downwelling longwave radiation, near-surface temperature, mean Sea level pressure, and Sea Ice reductions, suggesting a feedback chain linking vegetation change to Sea Ice Dynamics. This study highlights the importance of including interactive vegetation Dynamics in modeling the Arctic climate system, particularly when predicting Sea Ice Dynamics. (Less)

  • The Interplay of Recent Vegetation and Sea Ice Dynamics—Results From a Regional Earth System Model Over the Arctic
    Geophysical Research Letters, 2020
    Co-Authors: Wenxin Zhang, Ralf Döscher, Torben Koenigk, Paul A. Miller, Christer Jansson, Patrick Samuelsson, Benjamin Smith
    Abstract:

    Recent accelerated warming over the Arctic coincides with Sea Ice reduction and shifting patterns of land cover. We use a state-of-the-art regional Earth system model, RCAO-GUESS, which comprises a dynamic vegetation model (LPJ-GUESS), a regional atmosphere model (RCA), and an ocean Sea Ice model (RCO), to explore the dynamic coupling between vegetation and Sea Ice during 1989–2011. Our results show that RCAO-GUESS captures recent trends in observed Sea Ice concentration and extent, with the inclusion of vegetation Dynamics resulting in larger, more realistic variations in summer and autumn than the model that does not account for vegetation Dynamics. Vegetation feedbacks induce concomitant changes in downwelling longwave radiation, near-surface temperature, mean Sea level pressure, and Sea Ice reductions, suggesting a feedback chain linking vegetation change to Sea Ice Dynamics. This study highlights the importance of including interactive vegetation Dynamics in modeling the Arctic climate system, particularly when predicting Sea Ice Dynamics. (Less)

D. S. Abbot - One of the best experts on this subject based on the ideXlab platform.

  • Sea-Ice Dynamics strongly promote Snowball Earth initiation and destabilize tropical Sea-Ice margins
    Climate of the Past, 2012
    Co-Authors: Aiko Voigt, D. S. Abbot
    Abstract:

    The Snowball Earth bifurcation, or runaway Ice- albedo feedback, is defined for particular boundary condi- tions by a critical CO2 and a critical Sea-Ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI) , dif- fers greatly among climate models. Here, we study the ef- fect of bare Sea-Ice albedo, Sea-Ice Dynamics and ocean heat transport on (CO2, SI) in the atmosphere-ocean gen- eral circulation model ECHAM5/MPI-OM with Marinoan ( 635 Ma) continents and solar insolation (94 % of mod- ern). In its standard setup, ECHAM5/MPI-OM initiates a Snowball Earth much more easily than other climate mod- els at (CO2, SI) (500 ppm, 55 %). Replacing the model's standard bare Sea-Ice albedo of 0.75 by a much lower value of 0.45, we find (CO 2, SI) (204 ppm, 70 %). This is consis- tent with previous work and results from net evaporation and local melting near the Sea-Ice margin. When we additionally disable Sea-Ice Dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a hundred times lower CO2: (CO2, SI) (2 ppm, 85 %). Therefore, the simulation of Sea-Ice Dynamics in ECHAM5/MPI-OM is a dominant determinant of its high critical CO2 for Snowball initiation relative to other mod- els. Ocean heat transport has no effect on the critical Sea-Ice cover and only slightly decreases the critical CO2. For dis- abled Sea-Ice Dynamics, the state with 85 % Sea-Ice cover is stabilized by the Jormungand mechanism and shares charac- teristics with the Jormungand climate states. However, there is no indication of the Jormungand bifurcation and hystere- sis in ECHAM5/MPI-OM. The state with 85 % Sea-Ice cover therefore is a soft Snowball state rather than a true Jor- mungand state. Overall, our results demonstrate that differ- ences in Sea-Ice Dynamics schemes can be at least as impor- tant as differences in Sea-Ice albedo for causing the spread in climate models' estimates of the Snowball Earth bifurca- tion. A detailed understanding of Snowball Earth initiation therefore requires future reSearch on Sea-Ice Dynamics to de- termine which model's simulation is most realistic.

  • Sea-Ice Dynamics strongly promote Snowball Earth initiation and destabilize tropical Sea-Ice margins
    2012
    Co-Authors: Aiko Voigt, D. S. Abbot
    Abstract:

    Abstract. The Snowball Earth bifurcation, or runaway Ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical Sea-Ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs greatly among climate models. Here, we revisit the initiation of a Snowball Earth in the atmosphere-ocean general circulation model ECHAM5/MPI-OM for Marinoan (~630 Ma) continents and solar insolation decreased to 94%. In its standard setup, ECHAM5/MPI-OM initiates a Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Previous work has shown that the Snowball Earth bifurcation can be pushed equatorward if a low bare Sea Ice albedo is assumed because bare Sea Ice is exposed by net evaporation in the descent region of the Hadley circulation. Consistent with this, when we replace the model's standard bare Sea-Ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI)* ≈ (204 ppm, 70%). When we additionally disable Sea-Ice Dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a much lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, both lowering the bare Sea-Ice albedo and disabling Sea-Ice Dynamics increase the critical Sea-Ice cover in ECHAM5/MPI-OM, but Sea-Ice Dynamics have a much larger influence on the critical CO2. For disabled Sea-Ice Dynamics, the state with 85% Sea-Ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no Jormungand bifurcation between this Jormungand-like state and states with mid-latitude Sea-Ice margins. Our results indicate that differences in Sea-Ice Dynamics schemes can be as important as Sea Ice albedo for causing the spread in climate model's estimates of the location of the Snowball Earth bifurcation.

Aiko Voigt - One of the best experts on this subject based on the ideXlab platform.

  • Sea-Ice Dynamics strongly promote Snowball Earth initiation and destabilize tropical Sea-Ice margins
    Climate of the Past, 2012
    Co-Authors: Aiko Voigt, D. S. Abbot
    Abstract:

    The Snowball Earth bifurcation, or runaway Ice- albedo feedback, is defined for particular boundary condi- tions by a critical CO2 and a critical Sea-Ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI) , dif- fers greatly among climate models. Here, we study the ef- fect of bare Sea-Ice albedo, Sea-Ice Dynamics and ocean heat transport on (CO2, SI) in the atmosphere-ocean gen- eral circulation model ECHAM5/MPI-OM with Marinoan ( 635 Ma) continents and solar insolation (94 % of mod- ern). In its standard setup, ECHAM5/MPI-OM initiates a Snowball Earth much more easily than other climate mod- els at (CO2, SI) (500 ppm, 55 %). Replacing the model's standard bare Sea-Ice albedo of 0.75 by a much lower value of 0.45, we find (CO 2, SI) (204 ppm, 70 %). This is consis- tent with previous work and results from net evaporation and local melting near the Sea-Ice margin. When we additionally disable Sea-Ice Dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a hundred times lower CO2: (CO2, SI) (2 ppm, 85 %). Therefore, the simulation of Sea-Ice Dynamics in ECHAM5/MPI-OM is a dominant determinant of its high critical CO2 for Snowball initiation relative to other mod- els. Ocean heat transport has no effect on the critical Sea-Ice cover and only slightly decreases the critical CO2. For dis- abled Sea-Ice Dynamics, the state with 85 % Sea-Ice cover is stabilized by the Jormungand mechanism and shares charac- teristics with the Jormungand climate states. However, there is no indication of the Jormungand bifurcation and hystere- sis in ECHAM5/MPI-OM. The state with 85 % Sea-Ice cover therefore is a soft Snowball state rather than a true Jor- mungand state. Overall, our results demonstrate that differ- ences in Sea-Ice Dynamics schemes can be at least as impor- tant as differences in Sea-Ice albedo for causing the spread in climate models' estimates of the Snowball Earth bifurca- tion. A detailed understanding of Snowball Earth initiation therefore requires future reSearch on Sea-Ice Dynamics to de- termine which model's simulation is most realistic.

  • Sea-Ice Dynamics strongly promote Snowball Earth initiation and destabilize tropical Sea-Ice margins
    2012
    Co-Authors: Aiko Voigt, D. S. Abbot
    Abstract:

    Abstract. The Snowball Earth bifurcation, or runaway Ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical Sea-Ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs greatly among climate models. Here, we revisit the initiation of a Snowball Earth in the atmosphere-ocean general circulation model ECHAM5/MPI-OM for Marinoan (~630 Ma) continents and solar insolation decreased to 94%. In its standard setup, ECHAM5/MPI-OM initiates a Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Previous work has shown that the Snowball Earth bifurcation can be pushed equatorward if a low bare Sea Ice albedo is assumed because bare Sea Ice is exposed by net evaporation in the descent region of the Hadley circulation. Consistent with this, when we replace the model's standard bare Sea-Ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI)* ≈ (204 ppm, 70%). When we additionally disable Sea-Ice Dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a much lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, both lowering the bare Sea-Ice albedo and disabling Sea-Ice Dynamics increase the critical Sea-Ice cover in ECHAM5/MPI-OM, but Sea-Ice Dynamics have a much larger influence on the critical CO2. For disabled Sea-Ice Dynamics, the state with 85% Sea-Ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no Jormungand bifurcation between this Jormungand-like state and states with mid-latitude Sea-Ice margins. Our results indicate that differences in Sea-Ice Dynamics schemes can be as important as Sea Ice albedo for causing the spread in climate model's estimates of the location of the Snowball Earth bifurcation.