scholarly journals ATAT 1.0, an Automated Timing Accordance Tool for comparing ice-sheet model output with geochronological data

2018 ◽  
Author(s):  
Jeremy C. Ely ◽  
Chris D. Clark ◽  
David Small ◽  
Richard C. A. Hindmarsh
Keyword(s):  
Goodness Of Fit ◽  
Expert Knowledge ◽  
Numerical Models ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Model Performance ◽  
Geochronological Data ◽  
Improve Model ◽  
Geochronological Evidence ◽  
Ice Sheet Modelling

Abstract. Earth's extant ice sheets are of great societal importance given their ongoing and potential future contributions to sea-level rise. Numerical models of ice sheets are designed to simulate ice sheet behaviour in response to climate changes, but to be improved require validation against observations. The direct observational record of extant ice sheets is limited to a few recent decades, but there is a large and growing body of geochronological evidence spanning millennia constraining the behaviour of palaeo-ice sheets. Hindcasts can be used to improve model formulations and study interactions between ice sheets, the climate system and landscape. However, ice-sheet modelling results have inherent quantitative errors stemming from parameter uncertainty and their internal dynamics, leading many modellers to perform ensemble simulations, while uncertainty in geochronological evidence necessitates expert interpretation. Quantitative tools are essential to examine which members of an ice-sheet model ensemble best fit the constraints provided by geochronological data. We present an Automated Timing Accordance Tool (ATAT version 1.0) used to quantify differences between model results and geo-data on the timing of ice sheet advance and/or retreat. To demonstrate its utility, we perform three simplified ice-sheet modelling experiments of the former British-Irish Ice Sheet. These illustrate how ATAT can be used to quantify model performance, either by using the discrete locations where the data originated together with dating constraints or by comparing model outputs with empirically-derived reconstructions that have used these data along with wider expert knowledge. The ATAT code is made available and can be used by ice-sheet modellers to quantify the goodness of fit of hindcasts. ATAT may also be useful for highlighting data inconsistent with glaciological principles or reconstructions that cannot be replicated by an ice sheet model.

scholarly journals ATAT 1.1, the Automated Timing Accordance Tool for comparing ice-sheet model output with geochronological data

2019 ◽  
Vol 12 (3) ◽  
pp. 933-953 ◽  
Author(s):  
Jeremy C. Ely ◽  
Chris D. Clark ◽  
David Small ◽  
Richard C. A. Hindmarsh
Keyword(s):  
Goodness Of Fit ◽  
Expert Knowledge ◽  
Numerical Models ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Model Performance ◽  
Geochronological Data ◽  
Improve Model ◽  
Geochronological Evidence ◽  
Ice Sheet Modelling

Abstract. Earth's extant ice sheets are of great societal importance given their ongoing and potential future contributions to sea-level rise. Numerical models of ice sheets are designed to simulate ice-sheet behaviour in response to climate changes but to be improved require validation against observations. The direct observational record of extant ice sheets is limited to a few recent decades, but there is a large and growing body of geochronological evidence spanning millennia constraining the behaviour of palaeo-ice sheets. Hindcasts can be used to improve model formulations and study interactions between ice sheets, the climate system and landscape. However, ice-sheet modelling results have inherent quantitative errors stemming from parameter uncertainty and their internal dynamics, leading many modellers to perform ensemble simulations, while uncertainty in geochronological evidence necessitates expert interpretation. Quantitative tools are essential to examine which members of an ice-sheet model ensemble best fit the constraints provided by geochronological data. We present the Automated Timing Accordance Tool (ATAT version 1.1) used to quantify differences between model results and geochronological data on the timing of ice-sheet advance and/or retreat. To demonstrate its utility, we perform three simplified ice-sheet modelling experiments of the former British–Irish ice sheet. These illustrate how ATAT can be used to quantify model performance, either by using the discrete locations where the data originated together with dating constraints or by comparing model outputs with empirically derived reconstructions that have used these data along with wider expert knowledge. The ATAT code is made available and can be used by ice-sheet modellers to quantify the goodness of fit of hindcasts. ATAT may also be useful for highlighting data inconsistent with glaciological principles or reconstructions that cannot be replicated by an ice-sheet model.

8. Glaciers of the past

2018 ◽  
pp. 146-152
Author(s):  
David J. A. Evans
Keyword(s):  
Numerical Models ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Aerial Imagery ◽  
The Past ◽  
Glacial Landforms

To reconstruct the former extent and dynamics of ice sheets and glaciers requires a knowledge of process-form relationships that goes beyond individual landform types. Instead, glacial geomorphologists need to analyse large areas of glaciated terrain in a more holistic way, combining the whole range of glacial landforms and sediments to reconstruct glacier systems of the past, a subject now known as palaeoglaciology. ‘Glaciers of the past’ explains how the combination of aerial imagery and landform analysis is used in palaeoglaciological reconstruction. Increasingly powerful computers are making it possible to compile sophisticated numerical models that use our knowledge of glaciological processes and ice-core-derived palaeoclimate data to create three-dimensional glacier and ice sheet reconstructions.

scholarly journals Characterizing and reducing equifinality by constraining a distributed catchment model with regional signatures, local observations, and process understanding

2017 ◽  
Vol 21 (7) ◽  
pp. 3325-3352 ◽  
Author(s):  
Christa Kelleher ◽  
Brian McGlynn ◽  
Thorsten Wagener
Keyword(s):  
Goodness Of Fit ◽  
Snow Water Equivalent ◽  
Expert Knowledge ◽  
Model Performance ◽  
Hierarchical Approach ◽  
Catchment Scale ◽  
Distributed Modeling ◽  
Distributed Models ◽  
Knowledge Based ◽  
Behavioral Parameter

Abstract. Distributed catchment models are widely used tools for predicting hydrologic behavior. While distributed models require many parameters to describe a system, they are expected to simulate behavior that is more consistent with observed processes. However, obtaining a single set of acceptable parameters can be problematic, as parameter equifinality often results in several behavioral sets that fit observations (typically streamflow). In this study, we investigate the extent to which equifinality impacts a typical distributed modeling application. We outline a hierarchical approach to reduce the number of behavioral sets based on regional, observation-driven, and expert-knowledge-based constraints. For our application, we explore how each of these constraint classes reduced the number of behavioral parameter sets and altered distributions of spatiotemporal simulations, simulating a well-studied headwater catchment, Stringer Creek, Montana, using the distributed hydrology–soil–vegetation model (DHSVM). As a demonstrative exercise, we investigated model performance across 10 000 parameter sets. Constraints on regional signatures, the hydrograph, and two internal measurements of snow water equivalent time series reduced the number of behavioral parameter sets but still left a small number with similar goodness of fit. This subset was ultimately further reduced by incorporating pattern expectations of groundwater table depth across the catchment. Our results suggest that utilizing a hierarchical approach based on regional datasets, observations, and expert knowledge to identify behavioral parameter sets can reduce equifinality and bolster more careful application and simulation of spatiotemporal processes via distributed modeling at the catchment scale.

scholarly journals Pliocene Ice Sheet Modelling Intercomparison Project (PLISMIP) – experimental design

2012 ◽  
Vol 5 (4) ◽  
pp. 963-974 ◽  
Author(s):  
A. M. Dolan ◽  
S. J. Koenig ◽  
D. J. Hill ◽  
A. M. Haywood ◽  
R. M. DeConto
Keyword(s):  
Experimental Design ◽  
Sea Level ◽  
Atmospheric Carbon Dioxide ◽  
Climate Models ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Warm Period ◽  
Modern World ◽  
Intercomparison Project ◽  
Ice Sheet Modelling

Abstract. During the mid-Pliocene warm period (3.264 to 3.025 million years ago), global mean temperature was similar to that predicted for the next century and atmospheric carbon dioxide concentrations were slightly higher than today. Sea level was also higher than today, implying a reduction in the extent of the ice sheets. Thus, the mid-Pliocene warm period (mPWP) provides a unique testing ground to investigate the stability of the Earth's ice sheets and their contribution to sea level in a warmer-than-modern world. Climate models and ice sheet models can be used to enhance our understanding of ice sheet stability; however, uncertainties associated with different ice-sheet modelling frameworks mean that a rigorous comparison of numerical ice sheet model simulations for the Pliocene is essential. As an extension to the Pliocene Model Intercomparison Project (PlioMIP; Haywood et al., 2010, 2011a), the Pliocene Ice Sheet Modelling Intercomparison Project (PLISMIP) will provide the first assessment as to the ice sheet model dependency of ice sheet predictions for the mPWP. Here we outline the PLISMIP experimental design and initialisation conditions that have been adopted to simulate the Greenland and Antarctic ice sheets under present-day and warm mid-Pliocene conditions. Not only will this project provide a new benchmark in the simulation of ice sheets in a past warm period, but the analysis of model sensitivity to various uncertainties could directly inform future predictions of ice sheet and sea level change.

scholarly journals Ice sheet scale subglacial meltwater conduit dimensions and processes: insights from 3D morphometry of a large sample of eskers

2021 ◽  
Author(s):  
Robert Storrar ◽  
Andrew Jones ◽  
Frances Butcher ◽  
Nico Dewald ◽  
Chris Clark ◽  
...  
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Process Models ◽  
Cross Sectional ◽  
Large Sample ◽  
Subglacial Environment ◽  
Depositional Processes ◽  
Subglacial Meltwater

<p>Meltwater exerts an important influence on ice sheet dynamics and has attracted an increasing amount of attention over the last 20 years. However, the active subglacial environment remains difficult to study mainly due to its inaccessibility. Understanding of the dimensions, pattern, and extent of subglacial meltwater conduits at the ice sheet scale is limited to relatively sparse observations. We address this gap by using the geomorphological record of Quaternary ice sheets as a proxy to quantify the dimensions and pattern of subglacial conduits at the ice sheet scale. We present the results of a high-resolution (2 m), large sample (n>50,000) study of three-dimensional esker morphometry at sample locations in SW Finland and Nunavut, Canada. Detailed mapping of esker crestlines and outlines permits the quantification of a number of parameters, including: length, width, height, cross-sectional area, volume, sinuosity, cross-sectional symmetry, and uphill/downhill trends. Whilst the dimensions of eskers reflect depositional processes as well as simply the size of the parent conduit, they nevertheless offer a powerful tool for understanding the size and shape of meltwater conduits and the configuration of subglacial drainage systems across large areas (entire ice sheets), and over long periods of time (from years to thousands of years) in both high spatial and temporal resolution. The results may be used to: (1) inform numerical models of subglacial meltwater drainage, (2) inform process models of esker formation, and (3) provide a dataset of esker morphometry against which other features may be compared (e.g. sinuous ridges on Mars).</p>

scholarly journals Recent progress on combining geomorphological and geochronological data with ice sheet modelling, demonstrated using the last British–Irish Ice Sheet

2019 ◽  
Author(s):  
Jeremy C. Ely ◽  
Chris D. Clark ◽  
Richard C. A. Hindmarsh ◽  
Anna L. C. Hughes ◽  
Sarah L. Greenwood ◽  
...  
Keyword(s):  
Recent Progress ◽  
Ice Sheet ◽  
Geochronological Data ◽  
Ice Sheet Modelling

scholarly journals The EISMINT benchmarks for testing ice-sheet models

1996 ◽  
Vol 23 ◽  
pp. 1-12 ◽  
Author(s):  
Philippe Huybrechts ◽  
Tony Payne ◽  
Keyword(s):  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Time Dependent ◽  
Ice Thickness ◽  
Operation Model ◽  
Time Dependent Behaviour ◽  
Model Benchmark ◽  
Dependent Behaviour ◽  
Ice Sheet Modelling

We present a series of benchmark experiments designed for testing and comparing numerical ice-sheet models. Following the outcome of two EISMINT workshops organized to intercompare large-scale ice-sheet models currently in operation, model benchmark experiments ate described for ice sheets under fixed and moving margin conditions. These address both steady-state and time-dependent behaviour under schematic boundary conditions and with prescribed physics. A comparison was made of each model’s prediction of basic geophysical variables such as ice thickness, velocity and temperature. Consensus achieved in the model inter-comparison provides reference solutions against which the accuracy and consistency of ice-sheet modelling codes can be assessed.

scholarly journals Pliocene Ice Sheet Modelling Intercomparison Project (PLISMIP) – experimental design

2011 ◽  
Vol 4 (4) ◽  
pp. 2661-2686 ◽  
Author(s):  
A. M. Dolan ◽  
S. J. Koenig ◽  
D. J. Hill ◽  
A. M. Haywood ◽  
R. M. DeConto
Keyword(s):  
Experimental Design ◽  
Sea Level ◽  
Atmospheric Carbon Dioxide ◽  
Climate Models ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Warm Period ◽  
Modern World ◽  
Intercomparison Project ◽  
Ice Sheet Modelling

Abstract. During the mid-Pliocene Warm Period (3.264 to 3.025 million yr ago), global mean temperature was similar to that predicted for the next century and atmospheric carbon dioxide concentrations were slightly higher. Sea level was also higher than today, implying a reduction in the extent of the ice sheets. Thus, the mid-Pliocene Warm Period provides a unique testing ground to investigate the stability of the Earth's ice sheets and their contribution to sea level in a warmer-than-modern world. Climate models and ice sheet models can be used to enhance our understanding of ice sheet stability, however, uncertainties associated with different ice-sheet modelling frameworks/approaches mean that a rigorous comparison of numerical ice sheet model simulations for the Pliocene is essential. As an extension to the Pliocene Model Intercomparison Project (PlioMIP; Haywood et al., 2010, 2011a), the Pliocene Ice Sheet Modelling Intercomparison Project (PLISMIP) will address these uncertainties. Here we outline the PLISMIP experimental design and initialisation conditions that have been adopted to simulate the Greenland and Antarctic ice sheets under present day and warm mid-Pliocene conditions. Not only will this project provide a new benchmark in the simulation of ice sheets in a past warm period, but the analysis of model sensitivity to various uncertainties could directly inform future predictions of ice sheet and sea level change.

Time-scales and degrees of freedom operating in the evolution of continental ice-sheets

1990 ◽  
Vol 81 (4) ◽  
pp. 371-384 ◽  
Author(s):  
Richard C. A. Hindmarsh
Keyword(s):  
Mass Balance ◽  
Degrees Of Freedom ◽  
Large Scale ◽  
Numerical Models ◽  
Perturbation Expansion ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Plane Flow ◽  
Surface Mass ◽  
Continental Ice Sheets

ABSTRACTComprehensible explanations of the operation of earth climate systems should consist of descriptions of the operation of a few degrees of freedoms. Qualitative interpretations of results from large-scale numerical models generally follow this principle, but do not render formal definitions of the precise nature of such degrees of freedom.At its simplest, ice-sheet kinematics requires knowledge of the evolving height and span. Rheology and surface mass-balance impose different requirements upon the co-evolution of these variables, meaning a two-degree of freedom model is over-prescribed. By means of a perturbation expansion about the analytic similarity solution for viscous spreading, eigenfunctions corresponding to degrees of freedom in the ice-sheet profile are obtained, and are used to decompose mass-balance distributions. Only a few eigenfunctions are needed to replicate numerical models, implying that ice-sheets in plane flow may operate with fewer than ten degrees of freedom.Unstable evolution of ice-sheets can occur, when the operation of a very large number of degrees of freedom can be manifested. Previous work is reviewed and new results for the unstable transformation of valley glaciers into ice-sheets are presented. Phasing of initiation may be an unpredictable phenomenon.

scholarly journals An exact solution for a steady, flowline marine ice sheet

2014 ◽  
Vol 60 (224) ◽  
pp. 1117-1125 ◽  
Author(s):  
Ed Bueler
Keyword(s):  
Exact Solution ◽  
Numerical Models ◽  
Plug Flow ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Thickness ◽  
Longitudinal Stress ◽  
Surface Mass ◽  
Continuity Equations ◽  
Grounding Line

AbstractG. Böðvarsson’s 1955 plug-flow solution for an Icelandic glacier problem is shown to be an exact solution to the steady form of the simultaneous stress-balance and mass-continuity equations widely used in numerical models of marine ice sheets. The solution, which has parabolic ice thickness and constant vertically integrated longitudinal stress, solves the steady shallow-shelf approximation with linear sliding on a flat bed. It has an elevation-dependent surface mass-balance rate and, in the interpretation given here, a contrived location-dependent ice hardness distribution. By connecting Böðvarsson’s solution to the Van der Veen (1983) solution for floating ice, we construct an exact solution to the ‘rapid-sliding’ marine ice-sheet problem, continuously across the grounding line. We exploit this exact solution to examine the accuracy of two numerical methods, one grid-free and the other based on a fixed, equally spaced grid.

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