Basal shear stress of the Ross ice streams from control method inversions

Joughin, Ian; MacAyeal, Douglas R.; Tulaczyk, S. M.

doi:10.1029/2003jb002960

Cited by 199 publications

(268 citation statements)

References 66 publications

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“…This is due to the fact that basal shear traction must satisfy the global stress balance (Joughin et al, 2004;Minchew et al, 2016). The basal drag and basal velocities from the linear sliding law used to initiate the subglacial hydrology model are therefore self consistent with the subsequent inversion results of the two non-linear sliding laws.…”

Section: Discussionsupporting

confidence: 52%

Incorporating modelled subglacial hydrology into inversions for basal drag

Koziol

Arnold²

2017

The Cryosphere

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Abstract. A key challenge in modelling coupled ice-flowsubglacial hydrology is initializing the state and parameters of the system. We address this problem by presenting a workflow for initializing these values at the start of a summer melt season. The workflow depends on running a subglacial hydrology model for the winter season, when the system is not forced by meltwater inputs, and ice velocities can be assumed constant. Key parameters of the winter run of the subglacial hydrology model are determined from an initial inversion for basal drag using a linear sliding law. The state of the subglacial hydrology model at the end of winter is incorporated into an inversion of basal drag using a non-linear sliding law which is a function of water pressure. We demonstrate this procedure in the Russell Glacier area and compare the output of the linear sliding law with two non-linear sliding laws. Additionally, we compare the modelled winter hydrological state to radar observations and find that it is in line with summer rather than winter observations.

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Section: Discussionsupporting

confidence: 52%

Incorporating modelled subglacial hydrology into inversions for basal drag

Koziol

Arnold²

2017

The Cryosphere

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“…In contrast to many previous inverse approaches in glaciology, often aiming to minimize the misfit in surface velocities to reconstruct basal shearing conditions (e.g. (MacAyeal, 1992), (Joughin et al, 2004)), the correction method used here does not rely on evaluation of cost function gradients to update model parameters. Pollard and DeConto (2012) recently presented a correction method in which the local surface height misfit is directly used to iteratively update basal slipperiness.…”

Section: Correction Methodsmentioning

confidence: 99%

“…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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“…A common approach in the cryosphere community to obtain gradients of forward models has been to rely on the adjoint method (MacAyeal, 1993;Rommelaere andMacAyeal, 1997 Vieli andPayne, 2003;Joughin et al, 2004b;Larour et al, 2005;Vieli et al, 2006;Khazendar et al, 2007Khazendar et al, , 2009Morlighem et al, 2010;Arthern and Gudmundsson, 2010). The approach consists in analytically deriving the adjoint state of the forward model, which allows for an easy computation of the The Cryosphere, 8, 2335-2351, 2014…”

Section: Algorithmic Differentiation Of the Gradient Of Jmentioning

confidence: 99%

Inferred basal friction and surface mass balance of the Northeast Greenland Ice Stream using data assimilation of ICESat (Ice Cloud and land Elevation Satellite) surface altimetry and ISSM (Ice Sheet System Model)

et al. 2014

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Abstract. We present a new data assimilation method within the Ice Sheet System Model (ISSM) framework that is capable of assimilating surface altimetry data from missions such as ICESat (Ice Cloud and land Elevation Satellite) into reconstructions of transient ice flow. The new method relies on algorithmic differentiation to compute gradients of objective functions with respect to model forcings. It is applied to the Northeast Greenland Ice Stream, where surface mass balance and basal friction forcings are temporally inverted, resulting in adjusted modeled surface heights that best fit existing altimetry. This new approach allows for a better quantification of basal and surface processes and a better understanding of the physical processes currently missing in transient ice-flow models to better capture the important intra-and interannual variability in surface altimetry. It also demonstrates that large spatial and temporal variability is required in model forcings such as surface mass balance and basal friction, variability that can only be explained by including more complex processes such as snowpack compaction at the surface and basal hydrology at the bottom of the ice sheet. This approach is indeed a first step towards assimilating the wealth of high spatial resolution altimetry data available from EnviSat, ICESat, Operation IceBridge and CryoSat-2, and that which will be available in the near future with the launch of ICESat-2.

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Basal shear stress of the Ross ice streams from control method inversions

Cited by 199 publications

References 66 publications

Incorporating modelled subglacial hydrology into inversions for basal drag

Incorporating modelled subglacial hydrology into inversions for basal drag

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

Inferred basal friction and surface mass balance of the Northeast Greenland Ice Stream using data assimilation of ICESat (Ice Cloud and land Elevation Satellite) surface altimetry and ISSM (Ice Sheet System Model)

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