An iterative process for efficient optimisation of parameters in geoscientific models: a demonstration using the Parallel Ice Sheet Model (PISM) version 0.7.3

Abstract. Physical processes within geoscientific models are sometimes described by simplified schemes known as parameterisations. The values of the parameters within these schemes can be poorly constrained by theory or observation. Uncertainty in the parameter values translates into uncertainty in the outputs of the models. Proper quantification of the uncertainty in model predictions therefore requires a systematic approach for sampling parameter space. In this study, we develop a simple and efficient approach to identify regions of multi-dimensional parameter space that are consistent with observations. Using the Parallel Ice Sheet Model to simulate the present-day state of the Antarctic Ice Sheet, we find that co-dependencies between parameters preclude any simple identification of a single optimal set of parameter values. Approaches such as large ensemble modelling are therefore required in order to generate model predictions that incorporate proper quantification of the uncertainty arising from the parameterisation of physical processes.

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An iterative process for efficient optimisation of parameters in geoscientific models: a demonstration using the Parallel Ice Sheet Model (PISM) version 0.7.3

10.5194/gmd-2020-382 ◽

2020 ◽

Author(s):

Steven J. Phipps ◽

Jason L. Roberts ◽

Matt A. King

Keyword(s):

Parameter Space ◽

Ice Sheet ◽

Physical Processes ◽

Dimensional Parameter ◽

Model Predictions ◽

Observation Uncertainty ◽

Parameter Values ◽

The Antarctic ◽

Optimal Set ◽

Generate Model

Abstract. Physical processes within geoscientific models are sometimes described by simplified schemes known as parameterisations. The values of the parameters within these schemes can be poorly constrained by theory or observation. Uncertainty in the parameter values translates into uncertainty in the outputs of the models. Proper quantification of the uncertainty in model predictions therefore requires a systematic approach for sampling parameter space. In this study, we develop a simple and efficient approach to identify regions of multi-dimensional parameter space that are consistent with observations. Using the Parallel Ice Sheet Model to simulate the present-day state of the Antarctic Ice Sheet, we find that co-dependencies between parameters preclude the identification of a single optimal set of parameter values. Approaches such as large ensemble modelling are therefore required in order to generate model predictions that incorporate proper quantification of the uncertainty arising from the parameterisation of physical processes.

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Exploring parameter uncertainty in a model of the Antarctic Ice Sheet

10.5194/egusphere-egu21-15304 ◽

2021 ◽

Author(s):

Steven Phipps ◽

Jason Roberts ◽

Matt King

Keyword(s):

Parameter Space ◽

Ice Sheet ◽

Physical Processes ◽

Dimensional Parameter ◽

Antarctic Ice Sheet ◽

Model Predictions ◽

Global Sea Level ◽

Observation Uncertainty ◽

Parameter Values ◽

The Antarctic

Physical processes within ice sheet models are sometimes described by simplified schemes known as parameterisations. The values of the parameters within these schemes can be poorly constrained by theory or observation. Uncertainty in the parameter values translates into uncertainty in the outputs of the models. Proper quantification of the uncertainty in model predictions therefore requires a systematic approach for sampling parameter space. We demonstrate a simple and efficient approach to identify regions of multi-dimensional parameter space that are consistent with observations. Using the Parallel Ice Sheet Model to simulate the present-day state of the Antarctic Ice Sheet, we find that co-dependencies between parameters preclude the identification of a single optimal set of parameter values. Approaches such as large ensemble modelling are therefore required in order to generate model predictions, such as projections of future global sea level rise, that incorporate proper quantification of the uncertainty arising from the parameterisation of physical processes.

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Modelling the Antarctic Ice Sheet in the warm Mid-Pliocene

10.5194/egusphere-egu2020-19348 ◽

2020 ◽

Author(s):

James O'Neill ◽

Tamsin Edwards ◽

Lauren Gregoire ◽

Niall Gandy ◽

Aisling Dolan ◽

...

Keyword(s):

Sea Level ◽

Climate Models ◽

Phase 1 ◽

Ice Sheet ◽

Latin Hypercube Design ◽

Antarctic Ice Sheet ◽

Sea Levels ◽

Ocean Climate ◽

Parameter Values ◽

The Antarctic

The Antarctic ice sheet is a deeply uncertain component of future sea level under anthropogenic climate change. To shed light on the ice sheets response to warmer climates in the past and its&#8217; response to future warming, periods in Earth&#8217;s geological record can serve as instructive modelling targets. The mid-Pliocene warm period (3.3 &#8211; 3.0 Ma) is characterised by global mean surface temperatures ~2.7-4oC above pre-industrial, atmospheric CO2&#160;concentrations of ~400ppm&#160;and eustatic sea level rise on the order of ~10-30m above modern. The mid-Pliocene sea level record is subject to large uncertainties. The upper end of this record implies a significant contribution from Antarctica and possible collapse of regions of the ice sheet, driven by marine ice sheet instabilities.We present a suite of BISICLES ice sheet model&#160;simulations, forced with a subset of Pliocene Modelling Intercomparison Project (PlioMIP phase 1) coupled atmosphere-ocean climate models, that represent the Pliocene Antarctic ice sheet. This ensemble captures a range of possible ice sheet model responses to a warm Pliocene-like climate under different parameter choices, sampled in a Latin hypercube design. Modelled Antarctic sea level contribution is compared to reconstructions of Pliocene sea level, to explore the extent to which available data with large uncertainties can constrain the model parameter values.Our aim with this work is to provide insights on Antarctic contribution to sea level in the warm mid-Pliocene. We seek to characterise the role of ice-ocean, ice-atmosphere and ice-bedrock parameter uncertainty in BISICLES on the ice sheet sea level contribution range, and whether cliff instability processes are necessary in reproduce high Pliocene sea levels in this ice sheet model.

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Modelling the evolution of the Antarctic Ice Sheet since the last interglacial

The Cryosphere Discussions ◽

10.5194/tcd-8-85-2014 ◽

2014 ◽

Vol 8 (1) ◽

pp. 85-120 ◽

Cited By ~ 3

Author(s):

M. N. A. Maris ◽

S. R. M. Ligtenberg ◽

M. Crucifix ◽

B. de Boer ◽

J. Oerlemans

Keyword(s):

Ice Sheet ◽

Global Ocean ◽

Last Interglacial ◽

Antarctic Ice Sheet ◽

Velocity Parameter ◽

Ice Volume ◽

Reference Simulation ◽

Parameter Values ◽

The Antarctic ◽

Over Time

Abstract. We present the effects of changing two sliding parameters, a deformational velocity parameter and two bedrock deflection parameters on the evolution of the Antarctic Ice Sheet over the period from the last interglacial until the present. These sensitivity experiments have been conducted by running the ice-dynamical model ANICE forward in time. The climatological forcing over time is established by interpolating between two climate states from a regional climate model over time. The interpolation is done in such a way that both temperature and surface mass balance follow the Epica Dome C ice-core proxy record for temperature. We have determined an optimal set of parameter values, for which a realistic grounding line retreat history and present-day ice sheet can be simulated, the simulation with this set of parameter values is defined as the reference simulation. An increase of sliding with respect to this reference simulation leads to a decrease of the Antarctic ice volume due to enhanced ice velocities on mainly the West Antarctic Ice Sheet. The effect of changing the deformational velocity parameter mainly yields a change in East-Antarctic ice volume. Furthermore, we have found a minimum in the Antarctic ice volume during the mid-Holocene. This is a robust feature in our model results, where the strength and the timing of this minimum are both dependent on the investigated parameters. More sliding and a slower responding bedrock lead to a stronger minimum which emerges at an earlier time. From the model results we conclude that the Antarctic Ice Sheet has contributed 10.7 ± 1.3 m of eustatic sea level to the global ocean from the Last Glacial Maximum (about 16 kyr ago for the Antarctic Ice Sheet) until the present.

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A Numerical Investigation of Phase-Locked and Chaotic Behavior of Coupled Van Der Pol Oscillators

Volume 3A: 15th Biennial Conference on Mechanical Vibration and Noise — Vibration of Nonlinear, Random, and Time-Varying Systems ◽

10.1115/detc1995-0275 ◽

1995 ◽

Author(s):

Per G. Reinhall ◽

Duane W. Storti

Keyword(s):

Parameter Space ◽

Chaotic Behavior ◽

Van Der Pol Oscillator ◽

Stable Phase ◽

Phase Lag ◽

Van Der Pol ◽

Dimensional Parameter ◽

Existence And Stability ◽

Van Der Pol Oscillators ◽

Parameter Values

Abstract This paper presents the results of numerical simulations of the dynamics of a pair of linearly coupled van der Pol oscillators. A four-dimensional parameter space (including the displacement and velocity coupling strengths and the detuning in addition to the usual non-linearity parameter of the uncoupled van der Pol oscillator) is explored. In addition to corroboration of analytical results for the existence and stability of the in-phase and out-of-phase modes, regions in the parameter space are obtained where stable phase-locked motions exist with phase differences other than 0° or 180°. The dependence of stable phase lag on parameter values is presented for representative portions of the parameter space. A region is also located where trajectories are obtained which provide the first evidence of chaotic behavior and strange at tractors in this system of unforced non-conservative oscillators.

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Modelling the evolution of the Antarctic ice sheet since the last interglacial

The Cryosphere ◽

10.5194/tc-8-1347-2014 ◽

2014 ◽

Vol 8 (4) ◽

pp. 1347-1360 ◽

Cited By ~ 20

Author(s):

M. N. A. Maris ◽

B. de Boer ◽

S. R. M. Ligtenberg ◽

M. Crucifix ◽

W. J. van de Berg ◽

...

Keyword(s):

Climate Model ◽

Ice Sheet ◽

Global Ocean ◽

Last Interglacial ◽

Antarctic Ice Sheet ◽

Velocity Parameter ◽

Ice Volume ◽

Reference Simulation ◽

Parameter Values ◽

The Antarctic

Abstract. We present the effects of changing two sliding parameters, a deformational velocity parameter and two bedrock deflection parameters on the evolution of the Antarctic ice sheet over the period from the last interglacial until the present. These sensitivity experiments have been conducted by running the dynamic ice model ANICE forward in time. The temporal climatological forcing is established by interpolating between two temporal climate states created with a regional climate model. The interpolation is done in such a way that both temperature and surface mass balance follow the European Project for Ice Coring in Antarctica (EPICA) Dome C ice-core proxy record for temperature. We have determined an optimal set of parameter values, for which a realistic grounding-line retreat history and present-day ice sheet can be simulated; the simulation with this set of parameter values is defined as the reference simulation. An increase of sliding with respect to this reference simulation leads to a decrease of the Antarctic ice volume due to enhanced ice velocities on mainly the West Antarctic ice sheet. The effect of changing the deformational velocity parameter mainly yields a change in east Antarctic ice volume. Furthermore, we have found a minimum in the Antarctic ice volume during the mid-Holocene, in accordance with observations. This is a robust feature in our model results, where the strength and the timing of this minimum are both dependent on the investigated parameters. More sliding and a slower responding bedrock lead to a stronger minimum which emerges at an earlier time. From the model results, we conclude that the Antarctic ice sheet has contributed 10.7 ± 1.3 m of eustatic sea level to the global ocean from the last glacial maximum (about 16 ka for the Antarctic ice sheet) until the present.

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A simple model for showing effects of geometry on the ocean tides

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1979.0103 ◽

1979 ◽

Vol 367 (1731) ◽

pp. 549-571 ◽

Cited By ~ 3

Keyword(s):

Simple Model ◽

Southern Ocean ◽

Parameter Space ◽

Resonance Line ◽

Analytic Solutions ◽

Dimensional Parameter ◽

The Mean ◽

Two Parameters ◽

Parameter Values ◽

Made In

There is a need for a simple model to show effects of ocean shape on the tides and, in particular, to show how the Atlantic tides interact with those of the Southern Ocean. In response to this need, the Atlantic and Southern Oceans are here represented by narrow canals which meet in a T-junction. Analytic solutions for this geometry are easily obtained. Rotation effects can be included by calculating the second terms in an expansion in a small parameter proportional to the widths of the canals, and this can produce a realistic configuration of cotidal lines. The solution is studied in a two dimensional parameter space, the two parameters corresponding to the ocean depth and the mean latitude of the Southern Ocean. The solution is very sensitive to parameter values near the resonance line, but also depends very much on position in parameter space relative to a special point on the resonance line where the equilibrium tide is orthogonal to the resonant free oscillation. With a small friction, solutions on one side of this point generally give southward propagation of tides in the Atlantic, while northward propagation is generally obtained for parameter values on the other side. The effect depends on the direction in which the phase of the free tide is shifted relative to that of the direct tide. Useful conclusions about some old controversies can be made in the light of these results.

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