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

Bonan, Bertrand; Nodet, Maëlle; Ritz, Catherine; Peyaud, Vincent

doi:10.5194/npg-21-569-2014

Cited by 17 publications

(16 citation statements)

References 48 publications

(51 reference statements)

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“…The optimal control theory approach can also be used when the observations are distributed through time [Arthern and Hindmarsh, 2003;Goldberg and Heimbach, 2013;Larour et al, 2014]. Other methods in use include Bayesian estimation [Berliner et al, 2008;Raymond and Gudmundsson, 2009], ensemble-based Monte Carlo methods [Tarasov et al, 2012], and the ensemble Kalman filter [Bonan et al, 2013]. A variety of iterative approaches to the inversion have also been developed [Arthern and Gudmundsson, 2010;Pollard and DeConto, 2012;van Pelt et al, 2013].…”

Section: Introductionmentioning

confidence: 99%

Flow speed within the Antarctic ice sheet and its controls inferred from satellite observations

2015

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Accurate dynamical models of the Antarctic ice sheet with carefully specified initial conditions and well-calibrated rheological parameters are needed to forecast global sea level. By adapting an inverse method previously used in electric impedance tomography, we infer present-day flow speeds within the ice sheet. This inversion uses satellite observations of surface velocity, snow accumulation rate, and rate of change of surface elevation to estimate the basal drag coefficient and an ice stiffness parameter that influences viscosity. We represent interior ice motion using a vertically integrated approximation to incompressible Stokes flow. This model represents vertical shearing within the ice and membrane stresses caused by horizontal stretching and shearing. Combining observations and model, we recover marked geographical variations in the basal drag coefficient. Relative changes in basal shear stress are smaller. No simple sliding law adequately represents basal shear stress as a function of sliding speed. Low basal shear stress predominates in central East Antarctica, where thick insulating ice allows liquid water at the base to lubricate sliding. Higher shear stress occurs in coastal East Antarctica, where a frozen bed is more likely. Examining Thwaites glacier in more detail shows that the slowest sliding often coincides with elevated basal topography. Differences between our results and a similar adjoint-based inversion suggest that inversion or regularization methods can influence recovered parameters for slow sliding and finer scales; on broader scales we recover a similar pattern of low basal drag underneath major ice streams and extensive regions in East Antarctica that move by basal sliding.

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Section: Introductionmentioning

confidence: 99%

Flow speed within the Antarctic ice sheet and its controls inferred from satellite observations

2015

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“…This method has been extended in a non-linear Bayesian framework by Raymond and Gudmundsson (2009) and applied to an Antarctic ice stream by Pralong and Gudmundsson (2011). Bonan et al (2014) have tested the performances of an ensemble Kalman filter on twin experiments using a shallow-ice flowline model. The adjoint method has been tested by Goldberg and Heimbach (2013) and Perego et al (2014) with models of different complexity.…”

Section: Introductionmentioning

confidence: 99%

Comparison of adjoint and nudging methods to initialise ice sheet model basal conditions

2016

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Abstract. Ice flow models are now routinely used to forecast the ice sheets' contribution to 21st century sea-level rise. For such short term simulations, the model response is greatly affected by the initial conditions. Data assimilation algorithms have been developed to invert for the friction of the ice on its bedrock using observed surface velocities. A drawback of these methods is that remaining uncertainties, especially in the bedrock elevation, lead to non-physical ice flux divergence anomalies resulting in undesirable transient effects. In this study, we compare two different assimilation algorithms based on adjoints and nudging to constrain both bedrock friction and elevation. Using synthetic twin experiments with realistic observation errors, we show that the two algorithms lead to similar performances in reconstructing both variables and allow the flux divergence anomalies to be significantly reduced.

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“…For example, for a grounded ice sheet modelled with a fixed-grid method (and assuming every parameter is perfectly known), the unknown variables are the ice thicknesses located at known positions (see, e.g. Bonan et al, 2014).…”

Section: Form Of the State Vector In The Moving Mesh Casementioning

confidence: 99%

“…In particular, DA has already been used with fixed and adaptive grid models in the context of moving boundary problems. In these cases, estimates outside the moving domain are generally non-physical and need to be reanalysed (Mathiot et al, 2012;Bonan et al, 2014). Furthermore, with fixed or adaptive grids, DA does not provide an explicit estimate of the extent of the domain; this can be only done by interpolation.…”

Section: Introductionmentioning

confidence: 99%

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Data assimilation for moving mesh methods with an application to ice sheet modelling

Bonan

Nichols

Baines

et al. 2017

Nonlin. Processes Geophys.

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Abstract. We develop data assimilation techniques for nonlinear dynamical systems modelled by moving mesh methods. Such techniques are valuable for explicitly tracking interfaces and boundaries in evolving systems. The unique aspect of these assimilation techniques is that both the states of the system and the positions of the mesh points are updated simultaneously using physical observations. Covariances between states and mesh points are generated either by a correlation structure function in a variational context or by ensemble methods. The application of the techniques is demonstrated on a one-dimensional model of a grounded shallow ice sheet. It is shown, using observations of surface elevation and/or surface ice velocities, that the techniques predict the evolution of the ice sheet margin and the ice thickness accurately and efficiently. This approach also allows the straightforward assimilation of observations of the position of the ice sheet margin.

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

Cited by 17 publications

References 48 publications

Flow speed within the Antarctic ice sheet and its controls inferred from satellite observations

Flow speed within the Antarctic ice sheet and its controls inferred from satellite observations

Comparison of adjoint and nudging methods to initialise ice sheet model basal conditions

Data assimilation for moving mesh methods with an application to ice sheet modelling

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