The basal stress distribution of Ice Stream E, Antarctica, inferred by control methods

MacAyeal, Douglas R.

doi:10.1029/91jb02454

Cited by 188 publications

(185 citation statements)

References 13 publications

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“…[46] We use a partial differential equation constrained optimization algorithm similar to MacAyeal [1992], which consists in a gradient minimization of a cost function that measures the misfit between observed (u obs , v obs ) and modeled (u, v) horizontal surface velocities. The algorithm calculates the gradient of the cost function with respect to the unknown parameter.…”

Section: Inverse Methodsmentioning

confidence: 99%

“…This is convenient because for a linear material law, the system of ice flow equations becomes self-adjoint. This assumption is not rigorous because viscosity depends on the strain rate, but this simplification allows an easy calculation of the adjoint state for all three ice flow models (SSA, BP and FS), is widely used in the literature [MacAyeal, 1992[MacAyeal, , 1993 and has a limited impact on the control method convergence [Goldberg and Sergienko, 2011].…”

Section: Inverse Methodsmentioning

confidence: 99%

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Dynamically and Observationally Constrained Estimates of Water-Mass Distributions and Ages in the Global Ocean

DeVries

Primeau

2011

Journal of Physical Oceanography

183

202

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[1] Ice flow models used to project the mass balance of ice sheets in Greenland and Antarctica usually rely on the Shallow Ice Approximation (SIA) and the Shallow-Shelf Approximation (SSA), sometimes combined into so-called "hybrid" models. Such models, while computationally efficient, are based on a simplified set of physical assumptions about the mechanical regime of the ice flow, which does not uniformly apply everywhere on the ice sheet/ice shelf system, especially near grounding lines, where rapid changes are taking place at present. Here, we present a new thermomechanical finite element model of ice flow named ISSM (Ice Sheet System Model) that includes higher-order stresses, high spatial resolution capability and data assimilation techniques to better capture ice dynamics and produce realistic simulations of ice sheet flow at the continental scale. ISSM includes several approximations of the momentum balance equations, ranging from the two-dimensional SSA to the three-dimensional full-Stokes formulation. It also relies on a massively parallelized architecture and state-of-the-art scalable tools. ISSM employs data assimilation techniques, at all levels of approximation of the momentum balance equations, to infer basal drag at the ice-bed interface from satellite radar interferometry-derived observations of ice motion. Following a validation of ISSM with standard benchmarks, we present a demonstration of its capability in the case of the Greenland Ice Sheet. We show ISSM is able to simulate the ice flow of an entire ice sheet realistically at a high spatial resolution, with higher-order physics, thereby providing a pathway for improving projections of ice sheet evolution in a warming climate.Citation: Larour, E., H. Seroussi, M. Morlighem, and E. Rignot (2012), Continental scale, high order, high spatial resolution, ice sheet modeling using the Ice Sheet System Model (ISSM),

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Section: Inverse Methodsmentioning

confidence: 99%

Section: Inverse Methodsmentioning

confidence: 99%

Dynamically and Observationally Constrained Estimates of Water-Mass Distributions and Ages in the Global Ocean

DeVries

Primeau

2011

Journal of Physical Oceanography

183

202

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“…DA is widely known in weather and oceanography forecasting, but its introduction in glaciology is fairly recent, in particular for the initial state estimation problem for sea-level rise. MacAyeal (1992) and MacAyeal (1993) introduced control methods to infer basal drag in ice-stream models, using in particular the self-adjoint property of such models, leading to many application papers (Rommelaere and MacAyeal, 1997;Vieli and Payne, 2003), and later for full Stokes models (Morlighem et al, 2010;Jay-Allemand et al, 2011). Later on, many DA and inverse methods were introduced in glaciology.…”

Section: Introductionmentioning

confidence: 99%

An ETKF approach for initial state and parameter estimation in ice sheet modelling

Bonan

Nodet

Ritz

et al. 2014

Nonlin. Processes Geophys.

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Abstract. Estimating the contribution of Antarctica andGreenland to sea-level rise is a hot topic in glaciology. Good estimates rely on our ability to run a precisely calibrated ice sheet evolution model starting from a reliable initial state. Data assimilation aims to provide an answer to this problem by combining the model equations with observations. In this paper we aim to study a state-of-the-art ensemble Kalman filter (ETKF) to address this problem. This method is implemented and validated in the twin experiments framework for a shallow ice flowline model of ice dynamics. The results are very encouraging, as they show a good convergence of the ETKF (with localisation and inflation), even for small-sized ensembles.

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“…Surface data are much more abundant and, when linked to basal parameters using a forward model, can be used in an inverse manner to better constrain basal boundary conditions (e.g. MacAyeal, 1992;Joughin et al, 2004;Raymond Pralong and Gudmundsson, 2011). In this study, we focus on reconstructing basal topography.…”

Section: Introductionmentioning

confidence: 99%

An iterative inverse method to estimate basal topography and initialize ice flow models

et al. 2013

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Abstract.We evaluate an inverse approach to reconstruct distributed bedrock topography and simultaneously initialize an ice flow model. The inverse method involves an iterative procedure in which an ice dynamical model (PISM) is run multiple times over a prescribed period, while being forced with space-and time-dependent climate input. After every iteration bed heights are adjusted using information of the remaining misfit between observed and modeled surface topography. The inverse method is first applied in synthetic experiments with a constant climate forcing to verify convergence and robustness of the approach in three dimensions. In a next step, the inverse approach is applied to Nordenskiöldbreen, Svalbard, forced with height-and timedependent climate input since 1300 AD. An L-curve stopping criterion is used to prevent overfitting. Validation against radar data reveals a high correlation (up to R = 0.89) between modeled and observed thicknesses. Remaining uncertainties can mainly be ascribed to inaccurate model physics, in particular, uncertainty in the description of sliding. Results demonstrate the applicability of this inverse method to reconstruct the ice thickness distribution of glaciers and ice caps. In addition to reconstructing bedrock topography, the method provides a direct tool to initialize ice flow models for forecasting experiments.

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The basal stress distribution of Ice Stream E, Antarctica, inferred by control methods

Cited by 188 publications

References 13 publications

Dynamically and Observationally Constrained Estimates of Water-Mass Distributions and Ages in the Global Ocean

Dynamically and Observationally Constrained Estimates of Water-Mass Distributions and Ages in the Global Ocean

An ETKF approach for initial state and parameter estimation in ice sheet modelling

An iterative inverse method to estimate basal topography and initialize ice flow models

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