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  • 1
    Article
    Article
    Was ist eigentlich Klima? : Klima und Klimaänderungen (2015)
    Associated volumes
    Details Availability
    In: Expedition Erde, Bremen : MARUM - Zentrum für Marine Umweltwissenschaften, 2015, (2015), Seite 352-359, 9783000490453
    In: year:2015
    In: pages:352-359
    Type of Medium: Article
    Pages: Ill.
    Language: German
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  • 2
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    Comparison of hybrid schemes for the combination of shallow approximations in numerical simulations of the Antarctic Ice Sheet (2017)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 11 (1). pp. 247-265.
    Details
    Publication Date: 2018-12-17
    Description: The shallow ice approximation (SIA) is commonly used in ice-sheet models to simplify the force balance equations within the ice. However, the SIA cannot adequately reproduce the dynamics of the fast flowing ice streams usually found at the margins of ice sheets. To overcome this limitation, recent studies have introduced heuristic hybrid combinations of the SIA and the shelfy stream approximation. Here, we implement four different hybrid schemes into a model of the Antarctic Ice Sheet in order to compare their performance under present-day conditions. For each scheme, the model is calibrated using an iterative technique to infer the spatial variability in basal sliding parameters. Model results are validated against topographic and velocity data. Our analysis shows that the iterative technique compensates for the differences between the schemes, producing similar ice-sheet configurations through quantitatively different results of the sliding coefficient calibration. Despite this we observe a robust agreement in the reconstructed patterns of basal sliding parameters. We exchange the calibrated sliding parameter distributions between the schemes to demonstrate that the results of the model calibration cannot be straightforwardly transferred to models based on different approximations of ice dynamics. However, easily adaptable calibration techniques for the potential distribution of basal sliding coefficients can be implemented into ice models to overcome such incompatibility, as shown in this study
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/tc-11-247-2017
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison (2018)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 12 (4). pp. 1433-1460.
    Details
    Publication Date: 2018-12-17
    Description: Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/tc-12-1433-2018
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    initMIP-Antarctica: an ice sheet model initialization experiment of ISMIP6 (2019)
    Copernicus Publications (EGU)
    In:  The Cryosphere, 13 (5). pp. 1441-1471.
    Details
    Publication Date: 2021-01-08
    Description: Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMIP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMIP-Greenland, initMIP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMIP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/tc-13-1441-2019
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Simulation of the future sea level contribution of Greenland with a new glacial system model (2018)
    Copernicus Publications (EGU)
    In:  The Cryosphere Discussions . pp. 1-37.
    Details
    Publication Date: 2018-09-03
    Description: We introduce the coupled model of the Greenland glacial system IGLOO 1.0, including the polythermal ice sheet model SICOPOLIS (version 3.3) with hybrid dynamics, the model of basal hydrology HYDRO and a parameterization of submarine melt for marine-terminated outlet glaciers. Aim of this glacial system model is to gain a better understanding of the processes important for the future contribution of the Greenland ice sheet to sea level rise under future climate change scenarios. The ice sheet is initialized via a relaxation towards observed surface elevation, imposing the palaeo-surface temperature over the last glacial cycle. As a present-day reference, we use the 1961-1990 standard climatology derived from simulations of the regional atmosphere model MAR with ERA reanalysis boundary conditions. For the palaeo-part of the spin-up, we add the temperature anomaly derived from the GRIP ice core to the years 1961–1990 average surface temperature field. For our projections, we apply surface temperature and surface mass balance anomalies derived from RCP 4.5 and RCP 8.5 scenarios created by MAR with boundary conditions from simulations with three CMIP5 models. The hybrid ice sheet model is fully coupled with the model of basal hydrology. With this model and the MAR scenarios, we perform simulations to estimate the contribution of the Greenland ice sheet to future sea level rise until the end of the 21st and 23rd centuries. Further on, the impact of elevation-surface mass balance feedback, introduced via the MAR data, on future sea level rise is inspected. In our projections, we found the Greenland ice sheet to contribute to global sea level rise between 1.9 and 13.0cm until the year 2100 and between 3.5 and 76.4cm until the year 2300, including our simulated additional sea level rise due to elevation-surface mass balance feedback. Translated into additional sea level rise, the strength of this feedback in the year 2100 varies from 0.4 to 1.7cm, and in the year 2300 it ranges from 1.7 to 21.8cm. Additionally, taking Helheim and Store Glaciers as examples, we investigate the role of ocean warming and surface runoff change for the melting of outlet glaciers. It shows that ocean temperature and subglacial discharge are about equally important for the melting of the examined outlet glaciers.
    Type: Article , NonPeerReviewed
    Format: text
    DOI: 10.5194/tc-2018-23
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    OceanRep: Article in a Scientific Journal - without review
  • 6
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    Simulation of the future sea level contribution of Greenland with a new glacial system model (2018)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3The Cryosphere, COPERNICUS GESELLSCHAFT MBH, 12(10), pp. 3097-3121, ISSN: 1994-0424
    Details
    Publication Date: 2019-02-04
    Description: We introduce the coupled model of the Green- land glacial system IGLOO 1.0, including the polythermal ice sheet model SICOPOLIS (version 3.3) with hybrid dy- namics, the model of basal hydrology HYDRO and a param- eterization of submarine melt for marine-terminated outlet glaciers. The aim of this glacial system model is to gain a better understanding of the processes important for the future contribution of the Greenland ice sheet to sea level rise under future climate change scenarios. The ice sheet is initialized via a relaxation towards observed surface elevation, impos- ing the palaeo-surface temperature over the last glacial cycle. As a present-day reference, we use the 1961–1990 standard climatology derived from simulations of the regional atmo- sphere model MAR with ERA reanalysis boundary condi- tions. For the palaeo-part of the spin-up, we add the temper- ature anomaly derived from the GRIP ice core to the years 1961–1990 average surface temperature field. For our pro- jections, we apply surface temperature and surface mass bal- ance anomalies derived from RCP 4.5 and RCP 8.5 scenar- ios created by MAR with boundary conditions from simula- tions with three CMIP5 models. The hybrid ice sheet model is fully coupled with the model of basal hydrology. With this model and the MAR scenarios, we perform simulations to estimate the contribution of the Greenland ice sheet to future sea level rise until the end of the 21st and 23rd centuries. Fur- ther on, the impact of elevation–surface mass balance feed- back, introduced via the MAR data, on future sea level rise is inspected. In our projections, we found the Greenland ice sheet to contribute between 1.9 and 13.0 cm to global sea level rise until the year 2100 and between 3.5 and 76.4 cm until the year 2300, including our simulated additional sea level rise due to elevation–surface mass balance feedback. Translated into additional sea level rise, the strength of this feedback in the year 2100 varies from 0.4 to 1.7 cm, and in the year 2300 it ranges from 1.7 to 21.8 cm. Additionally, taking the Helheim and Store glaciers as examples, we inves- tigate the role of ocean warming and surface runoff change for the melting of outlet glaciers. It shows that ocean temper- ature and subglacial discharge are about equally important for the melting of the examined outlet glaciers.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 7
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    Simulations of the Greenland ice sheet with the ice sheet model SICOPOLIS including a fully coupled model of basal hydrology (2017)
    In:  EPIC3EGU General Assembly 2017, Vienna, 2017-04-24-2017-04-28
    Details
    Publication Date: 2017-05-08
    Description: We present simulations with the dynamic/thermodynamic ice sheet model SICOPOLIS (version 3) coupled to HYDRO, a model of basal hydrology. SICOPOLIS describes the evolution of ice thickness, temperature and water content of ice sheets. Recently, the treatment of longitudinal and lateral stresses (“shelfy stream approximation”) for the dynamics and the enthalpy method as an alternative method for solving the energy equation were included into the model. HYDRO describes the basal water transport using the hydrological potential. In a bi-directional coupling, HYDRO receives the basal water fluxes from SICOPOLIS, while the basal water from HYDRO affects the basal sliding in SICOPOLIS. Here, we present offline simulations with HYDRO as well as simulations with SICOPOLIS-only and the coupled model SICOPOLIS-HYDRO. Several sensitivity studies highlight the importance of basal processes. In particular, we inspect the role of horizontal resolution. It shows that not only horizontal resolution plays an important role for resolving outlet glaciers, but also the coupled model better reproduces outlet glaciers compared to the uncoupled one; even the North-East-Greenland Ice Stream is modelled quite well without the need for special regional tuning.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 8
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    Continuum-mechanical, Anisotropic Flow model for polar ice masses, based on an anisotropic Flow Enhancement factor (2018)
    Springer-Verlag | Springer-Verlag
    Details
    Publication Date: 2021-03-29
    Description: A complete theoretical presentation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor (CAFFE model) is given. The CAFFE model is an application of the theory of mixtures with continuous diversity for the case of large polar ice masses in which induced anisotropy occurs. The anisotropic response of the polycrystalline ice is described by a generalization of Glen’s flow law, based on a scalar anisotropic enhancement factor. The enhancement factor depends on the orientation mass density, which is closely related to the orientation distribution function and describes the distribution of grain orientations (fabric). Fabric evolution is governed by the orientation mass balance, which depends on four distinct effects, interpreted as local rigid body rotation, grain rotation, rotation recrystallization (polygonization) and grain boundary migration (migration recrystallization), respectively. It is proven that the flow law of the CAFFE model is truly anisotropic despite the collinearity between the stress deviator and stretching tensors.
    Keywords: Continuum mechanics; Anisotropy; Ice; Mixtures; Recrystallization ; 551 ; Physics; Theoretical and Applied Mechanics; Structural Materials; Engineering Thermodynamics, Heat and Mass Transfer; Classical Continuum Physics
    Type: article , publishedVersion
    Format: application/pdf
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    CITATION GEO-LEO
  • 9
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    Comparative simulations of the evolution of the Greenland ice sheet under simplified Paris Agreement scenarios with the models SICOPOLIS and ISSM (2019)
    In:  EPIC3Polar Science, 21, pp. 14-25, ISSN: 18739652
    Details
    Publication Date: 2019-11-18
    Description: Projections of the contribution of the Greenland ice sheet to sea level rise comprise uncertainties that arise from the imposed climate forcing and from the underlying mathematical and numerical description used by ice flow models. Here, we present a comparative modelling study with the models SICOPOLIS, using the shallow ice approximation (SIA) on a structured grid, and ISSM, using a higher-order (HO) approximation of the Stokes equation on an unstructured grid. Starting from a paleoclimatic spin-up produced by SICOPOLIS, the models are forced with two different, simplified warming scenarios based on RCP2.6 projections from climate models, which are in line with the limit of global warming negotiated for the Paris Agreement. ISSM/HO produces lower flow speeds at the glacier termini, but more acceleration in narrow outlet glaciers compared to SICOPOLIS/SIA. This leads to a larger elevation reduction for ISSM/HO, and thus a positive feedback on the surface mass balance (with that of ISSM/HO becoming ∼50 Gt a−1 more negative). Across the two models and scenarios, the projected mass loss by 2300 is ∼62–88 mm sea level equivalent.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 10
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    initMIP-Antarctica: an ice sheet model initialization experiment of ISMIP6 (2019)
    In:  EPIC3The Cryosphere, 13(5), pp. 1441-1471, ISSN: 1994-0424
    Details
    Publication Date: 2020-02-27
    Description: Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMIP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMIP-Greenland, initMIP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMIP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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    PAPER (OA)
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