Anthony Purcell - Academia.edu (original) (raw)

Papers by Anthony Purcell

Research paper thumbnail of Interplay of Altitude, Ground Track Coverage, Noise, and Regularization in the Spatial Resolution of GRACE Gravity Field Models

Journal Of Geophysical Research: Solid Earth, 2023

Models of the temporal gravity field derived from space gravity missions are typically produced w... more Models of the temporal gravity field derived from space gravity missions are typically produced with monthly temporal resolution and ∼300‐km spatial resolution. However, variations in instrument performance and altitude of the Gravity Recovery and Climate Experiment (GRACE) mission impact the spatial resolution that can be achieved month‐to‐month. As the altitude of the orbits of the twin spacecraft vary throughout the mission, so does the ability of the observations to recover certain components of the temporal gravity field. The spatial resolution of GRACE observations should increase as the altitude decreases throughout the mission because the reduced altitude intensifies the gravity signals acting on the satellites. Simulations using actual GRACE altitude and ground track coverage and realistic noise levels confirm this predicted influence of the altitude of the satellites on the accuracy of the estimated solutions. Solutions with larger mass concentration elements (mascons) are more numerically stable as the satellite altitude decreases but they suffer from greater error caused by the inability to properly represent spatial variations of signals within mascons, referred to as intramascon variability. Mascons as small as ∼150 × 150 km (i.e., ∼1.5 arc‐degree) reduce the intramascon variability and, with appropriate regularization, yield the most accurate solutions, especially during the low‐altitude periods of the GRACE mission. Importantly, unlike spherical harmonic solutions, regularized mascon solutions are not degraded during resonant orbit months, and are of comparable quality to months with full ground track coverage.

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Research paper thumbnail of Model of the western Laurentide Ice Sheet from glacio-isostatic adjustment analysis and revised margin locations

AGU Fall Meeting Abstracts, Dec 1, 2013

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Research paper thumbnail of The Role of Range Acceleration Observations and Regularisation in the Estimation of Sub-monthly Temporal Gravity Fields From GRACE Observations

AGU Fall Meeting Abstracts, Dec 1, 2017

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Research paper thumbnail of Revealing climate modes in steric sea levels: lessons learned from satellite geodesy, objective analyses and ocean reanalyses

AGU Fall Meeting Abstracts, Dec 1, 2017

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Research paper thumbnail of How errors in the calibration of GRACE accelerometers affect the estimates of temporal gravity fields

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Research paper thumbnail of Supplementary material to "ICESHEET 1.0: A program to produce paleo-ice sheet models with minimal assumptions&quot

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Research paper thumbnail of The impact that modelling ocean tides can have in the estimation of GRACE temporal gravity fields

AGU Fall Meeting Abstracts, Dec 1, 2016

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Research paper thumbnail of Satellite Gravimetry and the Gravitational Dirichlet Problem

AGU Fall Meeting Abstracts, Dec 1, 2016

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Research paper thumbnail of Assessing the uncertainties in the historical reconstructions of steric sea level changes

AGUFM, Dec 1, 2018

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Research paper thumbnail of 150 km ANU mascon solutions

<p>We present updated mascon solutions of the temporal gravity field, derived from ... more <p>We present updated mascon solutions of the temporal gravity field, derived from the analysis of Level-1B GRACE and GRACE-FO data using the range acceleration observable. Our previous solutions contained significant noise in particular regions of high mass loss (e.g. West Antarctica), which was caused by inappropriate levels of regularisation. Here we show a new approach of both iteration and regularisation of the solutions which generates more reliable estimates of the mass variations across the whole Earth, with both temporal and spatial consistency despite not applying any temporal or spatial inter-mascon constraints. We compare mascon solutions at spatial resolutions from 300 km to 100 km, show estimates of ocean mass increase and mass loss in ice-covered regions as well as assess the C20 time series estimated directly from GRACE data alone. Our new mascon estimates, at ~200 km x 200 km spatial resolution, are now publicly available.</p>

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Research paper thumbnail of Mitigation of thermal noise in GRACE accelerometer observations

Advances in Space Research, 2022

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Research paper thumbnail of An assessment of the ICE6G_C (VM5A) glacial isostatic adjustment model

EGUGA, Apr 1, 2016

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Research paper thumbnail of ANU GRACE Data Analysis: Orbit Modeling, Regularization and Inter‐satellite Range Acceleration Observations

Journal Of Geophysical Research: Solid Earth, Feb 1, 2022

Several different basis functions have been used to represent the Earth's gravity field in or... more Several different basis functions have been used to represent the Earth's gravity field in order to generate estimates of mass variations on Earth from the analysis of data of the Gravity Recovery and Climate Experiment (grace) and its successor grace Follow‐On missions, including spherical harmonics, mass concentration elements (mascons) and slepian functions. Each approach depends inherently upon accurate modeling of the orbits of the pair of satellites as they revolve around the Earth, so that the observations of inter‐satellite changes in range (or, more specifically, range rate) can be exploited to identify mass variations. We have developed software using a classical orbit modeling approach, mascons and 24‐hr orbit integration, to estimate simultaneously corrections to orbital parameters and the temporal gravity field from grace data. Rather than using the range rate, we use the range acceleration as the inter‐satellite observable as it aids in localizing the mass variations. Level‐1 B range acceleration observations contain high levels of high‐frequency noise that inhibits their usefulness for this purpose. Instead, we generate range acceleration observations by numerical differentiation of the Level‐1B range rate prefit residuals. Simulations show that the gravity signal is not attenuated in this process. Our monthly estimates of mass anomalies from grace data (2003–2016) agree well with previous studies, both spatially and temporally. When converted to spherical harmonics our time series of C2,0, derived from grace data alone, are close to the independent estimates from satellite laser ranging, but the overall solution is improved by substituting the SLR C2,0.

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Research paper thumbnail of Interplay of altitude, ground track coverage, noise and regularisation in the spatial resolution of GRACE gravity field models

<p>Models of the temporal gravity field derived from space gravity missions are typ... more <p>Models of the temporal gravity field derived from space gravity missions are typically produced with monthly temporal resolution and ~300 km spatial resolution. However, variations in instrument performance and altitude of the GRACE mission impact the spatial resolution that can be achieved month-to-month. As the altitude of the orbits of the twin spacecraft vary throughout the mission, so does the ability of the observations to recover certain components of the temporal gravity field. The spatial resolution of GRACE observations should increase as the altitude decreases throughout the mission because the reduced altitude intensifies the gravity signals acting on the satellites. Simulations using actual GRACE altitude and ground track coverage and realistic noise levels confirm this predicted influence of the altitude of the satellites on the accuracy of the estimated solutions. Solutions with larger mass concentration elements (mascons) are more numerically stable as the satellite altitude decreases but they suffer from greater error caused by the inability to properly represent spatial variations of signals within mascons, referred to as intra-mascon variability. Mascons as small as ~150 x 150 km (i.e. ~1.5 arc-degree) reduce the intra-mascon variability and, with appropriate regularisation, yield the most accurate solutions, especially during the low-altitude periods of the GRACE mission. Importantly, unlike spherical harmonic solutions, regularised mascon solutions are not degraded during resonant orbit months, and are of comparable quality to months with full ground track coverage.</p>

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Research paper thumbnail of ANU GRACE Data Analysis: Characteristics and Benefits of Using Irregularly Shaped Mascons

Journal of Geophysical Research: Solid Earth, 2022

The estimation of mass anomalies using Gravity Recovery and Climate Experiment (GRACE) data invol... more The estimation of mass anomalies using Gravity Recovery and Climate Experiment (GRACE) data involves parameterizing the temporal gravity field using basis functions. In this study, we show that the use of irregularly shaped mass concentration (mascon) tiles that follow land/ocean boundaries reduces the leakage of land signals into ocean regions and vice versa. Leakage of signal from continents to oceans in mascons that cross the coastline affect the integrated mass changes at a regional scale. For example, the calculated mass loss in 2016 is ∼5% greater for Greenland when using mascons that follow coastlines. We describe efficient algorithms for computing the accelerations acting on the satellites caused by mass changes on mascons, along with the partial derivatives relating the mass changes to the inter‐satellite observations. Through simulation, we quantify the impact of different mascon geometries, spatial resolution and regularization. The variations of mass change signals within mascons, which we call “intra‐mascon variability,” contribute to errors in estimates of mass variation from GRACE data. While this can be mitigated through the regularization of the inversions, it cannot be removed entirely. The use of irregularly shaped mascons that follow land/ocean boundaries reduces the “intra‐mascon leakage” of land signals into ocean regions and vice versa. This approach can also be applied to hydrological basins for calculating integrated mass changes on catchment scales.

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Research paper thumbnail of Holocene sea-level and paleoenvironmental reconstruction using radiocarbon local marine reservoir age and geophysical modeling in Tongatapu, Kingdom of Tonga

Japan Geoscience Union, 2019

Reconstructing the history of Holocene relative sea levels around Tonga is important for understa... more Reconstructing the history of Holocene relative sea levels around Tonga is important for understanding geomorphological theories and also interpreting paleoenvironmental and archaeological studies in that area. However, neither continuous sea level reconstructions nor quantitative paleoenvironmental studies using geochemical/physical methods are available. In this study, we reconstructed Holocene sea level changes in Tongatapu island using radiocarbon local marine reservoir age (ΔR) and glacio-hydro adjustment (GIA) modeling. Furthermore, we interpreted the relationship between the reduction of the size of bivalves (Gafrarium tumidum) and changes in their paleoenvironment. We suggest that ΔR results showed a sea surface salinity (SSS) decrease in the islands lagoon as relative sea level have been risen during the period between ~2.6 cal kyr BP to the present, and this can be attributed as closure of the lagoon. Moreover, the maximum sea level in mid-Holocene using GIA modeling sugge...

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Research paper thumbnail of A new Approach to Combine GRACE and ICESat Observations to Estimate Glacial Isostatic Adjustment in East Antarctic

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Research paper thumbnail of Holocene sea level reconstruction using lagoon specific local marine reservoir effect and geophysical modeling in Tongatapu, Kingdom of Tonga

Quaternary Science Reviews, 2020

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Research paper thumbnail of Reply to Comment by W. R. Peltier, D. F. Argus, and R. Drummond on “An Assessment of the ICE6G_C (VM5a) Glacial Isostatic Adjustment Model”

Journal of Geophysical Research: Solid Earth, 2018

The empirical approximation of Purcell et al. (2011, https://doi.org/10.1029/2011GL048624) has be... more The empirical approximation of Purcell et al. (2011, https://doi.org/10.1029/2011GL048624) has been validated by Peltier et al. (2018, https://doi.org/10.1002/2016JB013844). In their Comment they introduced new results derived from the same ice/rheology models of ICE6G_C (VM5a) but using a different model for Antarctic bathymetry. This has greatly reduced the differences in predicted Antarctic uplift rates relative to those of Purcell et al. (2016, https://doi.org/10.1002/2015JB012742). In fact, with a ∼50% reduction in uplift rate in the Weddell Sea, the results of Peltier et al. (2018, https://doi.org/10.1002/2016JB013844) now agree more closely with the predictions of Purcell et al. (2016, https://doi.org/10.1002/2015JB012742) than with the original ICE6G_C values. Peltier et al. (2018, https://doi.org/10.1002/2016JB013844) state that the high power in their high‐frequency spherical harmonic coefficients remains in their new calculations. They also claim that Purcell et al. (2016...

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Research paper thumbnail of ICESHEET 1.0: A program to produce paleo-ice sheet models with minimal assumptions

Geoscientific Model Development Discussions, 2016

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Research paper thumbnail of Interplay of Altitude, Ground Track Coverage, Noise, and Regularization in the Spatial Resolution of GRACE Gravity Field Models

Journal Of Geophysical Research: Solid Earth, 2023

Models of the temporal gravity field derived from space gravity missions are typically produced w... more Models of the temporal gravity field derived from space gravity missions are typically produced with monthly temporal resolution and ∼300‐km spatial resolution. However, variations in instrument performance and altitude of the Gravity Recovery and Climate Experiment (GRACE) mission impact the spatial resolution that can be achieved month‐to‐month. As the altitude of the orbits of the twin spacecraft vary throughout the mission, so does the ability of the observations to recover certain components of the temporal gravity field. The spatial resolution of GRACE observations should increase as the altitude decreases throughout the mission because the reduced altitude intensifies the gravity signals acting on the satellites. Simulations using actual GRACE altitude and ground track coverage and realistic noise levels confirm this predicted influence of the altitude of the satellites on the accuracy of the estimated solutions. Solutions with larger mass concentration elements (mascons) are more numerically stable as the satellite altitude decreases but they suffer from greater error caused by the inability to properly represent spatial variations of signals within mascons, referred to as intramascon variability. Mascons as small as ∼150 × 150 km (i.e., ∼1.5 arc‐degree) reduce the intramascon variability and, with appropriate regularization, yield the most accurate solutions, especially during the low‐altitude periods of the GRACE mission. Importantly, unlike spherical harmonic solutions, regularized mascon solutions are not degraded during resonant orbit months, and are of comparable quality to months with full ground track coverage.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Model of the western Laurentide Ice Sheet from glacio-isostatic adjustment analysis and revised margin locations

AGU Fall Meeting Abstracts, Dec 1, 2013

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Role of Range Acceleration Observations and Regularisation in the Estimation of Sub-monthly Temporal Gravity Fields From GRACE Observations

AGU Fall Meeting Abstracts, Dec 1, 2017

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Revealing climate modes in steric sea levels: lessons learned from satellite geodesy, objective analyses and ocean reanalyses

AGU Fall Meeting Abstracts, Dec 1, 2017

Bookmarks Related papers MentionsView impact

Research paper thumbnail of How errors in the calibration of GRACE accelerometers affect the estimates of temporal gravity fields

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Supplementary material to "ICESHEET 1.0: A program to produce paleo-ice sheet models with minimal assumptions&quot

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The impact that modelling ocean tides can have in the estimation of GRACE temporal gravity fields

AGU Fall Meeting Abstracts, Dec 1, 2016

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Satellite Gravimetry and the Gravitational Dirichlet Problem

AGU Fall Meeting Abstracts, Dec 1, 2016

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Assessing the uncertainties in the historical reconstructions of steric sea level changes

AGUFM, Dec 1, 2018

Bookmarks Related papers MentionsView impact

Research paper thumbnail of 150 km ANU mascon solutions

<p>We present updated mascon solutions of the temporal gravity field, derived from ... more <p>We present updated mascon solutions of the temporal gravity field, derived from the analysis of Level-1B GRACE and GRACE-FO data using the range acceleration observable. Our previous solutions contained significant noise in particular regions of high mass loss (e.g. West Antarctica), which was caused by inappropriate levels of regularisation. Here we show a new approach of both iteration and regularisation of the solutions which generates more reliable estimates of the mass variations across the whole Earth, with both temporal and spatial consistency despite not applying any temporal or spatial inter-mascon constraints. We compare mascon solutions at spatial resolutions from 300 km to 100 km, show estimates of ocean mass increase and mass loss in ice-covered regions as well as assess the C20 time series estimated directly from GRACE data alone. Our new mascon estimates, at ~200 km x 200 km spatial resolution, are now publicly available.</p>

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Research paper thumbnail of Mitigation of thermal noise in GRACE accelerometer observations

Advances in Space Research, 2022

Bookmarks Related papers MentionsView impact

Research paper thumbnail of An assessment of the ICE6G_C (VM5A) glacial isostatic adjustment model

EGUGA, Apr 1, 2016

Bookmarks Related papers MentionsView impact

Research paper thumbnail of ANU GRACE Data Analysis: Orbit Modeling, Regularization and Inter‐satellite Range Acceleration Observations

Journal Of Geophysical Research: Solid Earth, Feb 1, 2022

Several different basis functions have been used to represent the Earth's gravity field in or... more Several different basis functions have been used to represent the Earth's gravity field in order to generate estimates of mass variations on Earth from the analysis of data of the Gravity Recovery and Climate Experiment (grace) and its successor grace Follow‐On missions, including spherical harmonics, mass concentration elements (mascons) and slepian functions. Each approach depends inherently upon accurate modeling of the orbits of the pair of satellites as they revolve around the Earth, so that the observations of inter‐satellite changes in range (or, more specifically, range rate) can be exploited to identify mass variations. We have developed software using a classical orbit modeling approach, mascons and 24‐hr orbit integration, to estimate simultaneously corrections to orbital parameters and the temporal gravity field from grace data. Rather than using the range rate, we use the range acceleration as the inter‐satellite observable as it aids in localizing the mass variations. Level‐1 B range acceleration observations contain high levels of high‐frequency noise that inhibits their usefulness for this purpose. Instead, we generate range acceleration observations by numerical differentiation of the Level‐1B range rate prefit residuals. Simulations show that the gravity signal is not attenuated in this process. Our monthly estimates of mass anomalies from grace data (2003–2016) agree well with previous studies, both spatially and temporally. When converted to spherical harmonics our time series of C2,0, derived from grace data alone, are close to the independent estimates from satellite laser ranging, but the overall solution is improved by substituting the SLR C2,0.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Interplay of altitude, ground track coverage, noise and regularisation in the spatial resolution of GRACE gravity field models

<p>Models of the temporal gravity field derived from space gravity missions are typ... more <p>Models of the temporal gravity field derived from space gravity missions are typically produced with monthly temporal resolution and ~300 km spatial resolution. However, variations in instrument performance and altitude of the GRACE mission impact the spatial resolution that can be achieved month-to-month. As the altitude of the orbits of the twin spacecraft vary throughout the mission, so does the ability of the observations to recover certain components of the temporal gravity field. The spatial resolution of GRACE observations should increase as the altitude decreases throughout the mission because the reduced altitude intensifies the gravity signals acting on the satellites. Simulations using actual GRACE altitude and ground track coverage and realistic noise levels confirm this predicted influence of the altitude of the satellites on the accuracy of the estimated solutions. Solutions with larger mass concentration elements (mascons) are more numerically stable as the satellite altitude decreases but they suffer from greater error caused by the inability to properly represent spatial variations of signals within mascons, referred to as intra-mascon variability. Mascons as small as ~150 x 150 km (i.e. ~1.5 arc-degree) reduce the intra-mascon variability and, with appropriate regularisation, yield the most accurate solutions, especially during the low-altitude periods of the GRACE mission. Importantly, unlike spherical harmonic solutions, regularised mascon solutions are not degraded during resonant orbit months, and are of comparable quality to months with full ground track coverage.</p>

Bookmarks Related papers MentionsView impact

Research paper thumbnail of ANU GRACE Data Analysis: Characteristics and Benefits of Using Irregularly Shaped Mascons

Journal of Geophysical Research: Solid Earth, 2022

The estimation of mass anomalies using Gravity Recovery and Climate Experiment (GRACE) data invol... more The estimation of mass anomalies using Gravity Recovery and Climate Experiment (GRACE) data involves parameterizing the temporal gravity field using basis functions. In this study, we show that the use of irregularly shaped mass concentration (mascon) tiles that follow land/ocean boundaries reduces the leakage of land signals into ocean regions and vice versa. Leakage of signal from continents to oceans in mascons that cross the coastline affect the integrated mass changes at a regional scale. For example, the calculated mass loss in 2016 is ∼5% greater for Greenland when using mascons that follow coastlines. We describe efficient algorithms for computing the accelerations acting on the satellites caused by mass changes on mascons, along with the partial derivatives relating the mass changes to the inter‐satellite observations. Through simulation, we quantify the impact of different mascon geometries, spatial resolution and regularization. The variations of mass change signals within mascons, which we call “intra‐mascon variability,” contribute to errors in estimates of mass variation from GRACE data. While this can be mitigated through the regularization of the inversions, it cannot be removed entirely. The use of irregularly shaped mascons that follow land/ocean boundaries reduces the “intra‐mascon leakage” of land signals into ocean regions and vice versa. This approach can also be applied to hydrological basins for calculating integrated mass changes on catchment scales.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Holocene sea-level and paleoenvironmental reconstruction using radiocarbon local marine reservoir age and geophysical modeling in Tongatapu, Kingdom of Tonga

Japan Geoscience Union, 2019

Reconstructing the history of Holocene relative sea levels around Tonga is important for understa... more Reconstructing the history of Holocene relative sea levels around Tonga is important for understanding geomorphological theories and also interpreting paleoenvironmental and archaeological studies in that area. However, neither continuous sea level reconstructions nor quantitative paleoenvironmental studies using geochemical/physical methods are available. In this study, we reconstructed Holocene sea level changes in Tongatapu island using radiocarbon local marine reservoir age (ΔR) and glacio-hydro adjustment (GIA) modeling. Furthermore, we interpreted the relationship between the reduction of the size of bivalves (Gafrarium tumidum) and changes in their paleoenvironment. We suggest that ΔR results showed a sea surface salinity (SSS) decrease in the islands lagoon as relative sea level have been risen during the period between ~2.6 cal kyr BP to the present, and this can be attributed as closure of the lagoon. Moreover, the maximum sea level in mid-Holocene using GIA modeling sugge...

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Research paper thumbnail of A new Approach to Combine GRACE and ICESat Observations to Estimate Glacial Isostatic Adjustment in East Antarctic

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Holocene sea level reconstruction using lagoon specific local marine reservoir effect and geophysical modeling in Tongatapu, Kingdom of Tonga

Quaternary Science Reviews, 2020

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Reply to Comment by W. R. Peltier, D. F. Argus, and R. Drummond on “An Assessment of the ICE6G_C (VM5a) Glacial Isostatic Adjustment Model”

Journal of Geophysical Research: Solid Earth, 2018

The empirical approximation of Purcell et al. (2011, https://doi.org/10.1029/2011GL048624) has be... more The empirical approximation of Purcell et al. (2011, https://doi.org/10.1029/2011GL048624) has been validated by Peltier et al. (2018, https://doi.org/10.1002/2016JB013844). In their Comment they introduced new results derived from the same ice/rheology models of ICE6G_C (VM5a) but using a different model for Antarctic bathymetry. This has greatly reduced the differences in predicted Antarctic uplift rates relative to those of Purcell et al. (2016, https://doi.org/10.1002/2015JB012742). In fact, with a ∼50% reduction in uplift rate in the Weddell Sea, the results of Peltier et al. (2018, https://doi.org/10.1002/2016JB013844) now agree more closely with the predictions of Purcell et al. (2016, https://doi.org/10.1002/2015JB012742) than with the original ICE6G_C values. Peltier et al. (2018, https://doi.org/10.1002/2016JB013844) state that the high power in their high‐frequency spherical harmonic coefficients remains in their new calculations. They also claim that Purcell et al. (2016...

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Research paper thumbnail of ICESHEET 1.0: A program to produce paleo-ice sheet models with minimal assumptions

Geoscientific Model Development Discussions, 2016

Bookmarks Related papers MentionsView impact