13 research outputs found
Sensitivity of centennial mass loss projections of the Amundsen basin to the friction law
Reliable projections of ice sheets' future contributions to sea-level rise require models that are able to accurately simulate grounding-line
dynamics, starting from initial states consistent with observations. Here, we
simulate the centennial evolution of the Amundsen Sea Embayment in response
to a prescribed perturbation in order to assess the sensitivity of mass loss
projections to the chosen friction law, depending on the initialisation
strategy. To this end, three different model states are constructed by
inferring both the initial basal shear stress and viscosity fields with
various relative weights. Then, starting from each of these model states,
prognostic simulations are carried out using a Weertman, a Schoof and a Budd
friction law, with different parameter values. Although the sensitivity of
projections to the chosen friction law tends to decrease when more weight is
put on viscosity during initialisation, it remains significant for the most
physically acceptable of the constructed model states. Independently of the
considered model state, the Weertman law systematically predicts the lowest
mass losses. In addition, because of its particular dependence on effective
pressure, the Budd friction law induces significantly different grounding-line retreat patterns than the other laws and predicts significantly higher
mass losses.</p
Impact of mesh resolution for MISMIP and MISMIP3d experiments using Elmer/Ice
International audienceThe dynamical contribution of marine ice sheets to sea level rise is largely controlled by grounding line (GL) dynamics. Two marine ice sheet model intercomparison exercises , namely MISMIP and MISMIP3d, have been proposed to the community to test and compare the ability of models to capture the GL dynamics. Both exercises are known to present a discontinuity of the friction at the GL, which is believed to increase the model sensitivity to mesh resolution. Here, using Elmer/Ice, the only Stokes model which completed both intercomparisons, the sensitivity to the mesh resolution is studied from an extended MISMIP experiment in which the friction continuously decreases over a transition distance and equals zero at the GL. Using this MISMIP-like setup, it is shown that the sensitivity to the mesh resolution is not improved for a vanishing friction at the GL. For the original MISMIP experiment, i.e. for a discontinuous friction at the GL, we further show that the results are moreover very sensitive to the way the friction is interpolated in the close vicinity of the GL. In the light of these new insights, and thanks to increased computing resources, new results for the MISMIP3d experiments obtained for higher resolutions than previously published are made available for future comparisons as the Supplement
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initMIP-Antarctica: an ice sheet model initialization experiment of ISMIP6
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
InitMIP-Antarctica:An ice sheet model initialization experiment of ISMIP6
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
A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)
We present a comparison of the numerics and simulation results for two
"full" Stokes ice sheet models, FELIX-S (Leng et al. 2012) and Elmer/Ice (Gagliardini et al. 2013). The models are applied to the Marine Ice Sheet Model
Intercomparison Project for plan view models (MISMIP3d). For the diagnostic
experiment (P75D) the two models give similar results ( < 2 %
difference with respect to along-flow velocities) when using identical
geometries and computational meshes, which we interpret as an indication of
inherent consistencies and similarities between the two models. For the standard (Stnd),
P75S, and P75R prognostic experiments, we find that FELIX-S (Elmer/Ice)
grounding lines are relatively more retreated (advanced), results that are
consistent with minor differences observed in the diagnostic experiment
results and that we show to be due to different choices in the implementation
of basal boundary conditions in the two models. While we are not able to
argue for the relative favorability of either implementation, we do show that
these differences decrease with increasing horizontal (i.e., both along- and
across-flow) grid resolution and that grounding-line positions for FELIX-S
and Elmer/Ice converge to within the estimated truncation error for
Elmer/Ice. Stokes model solutions are often treated as an accuracy metric in
model intercomparison experiments, but computational cost may not always
allow for the use of model resolution within the regime of asymptotic
convergence. In this case, we propose that an alternative estimate for the
uncertainty in the grounding-line position is the span of grounding-line
positions predicted by multiple Stokes models
[Recurrent transient ischemic stroke in a young patient with papillary fibroelastoma of the mitral valve and hyperhomocysteinemia. A case report].
International audienceWe describe a case of a young patient admitted for recurrent ischemic stroke caused by a papillary fibroelastoma of the mitral valve and a hyperhomocysteinemia. A papillary fibroelastoma is a benign cardiac tumor which can be associated with serious embolic complications. A moderate plasma level of hyperhomocysteinemia is considered as a risk factor of ischemic stroke. The authors suggest that this association increases the risk of ischemic stroke in their patient. The tumor was surgically removed to avoid new embolic events associated with a vitamin B supplementation. After surgery and acid folic supplementation, no recurrence was observed
[Acute heart disease in search and rescue helicopter missions, from French Navy. A retrospective study from 2000 to 2007].
International audienceBACKGROUND: Search and rescue helicopters from the French navy conduct ambulance and search and rescue missions near the western coast of the French Britain. The team on board includes military doctor and paramedic. Operations in this area are challenging due to long distances and severe weather conditions. METHODS: We studied retrospectively 205 search and rescue missions from 2000 to 2007 with special emphasis on acute heart disease and operative conditions. RESULTS: 12.2% of the missions (25/205) concern acute heart disease dominated by myocardial infarction elevation myocardial infarction. All of the patients are male. Most of them are seafarers and the others come from ferries with a median age of 53.4 years. Sixty-two percent of the missions were carried in darkness. The median range is about 80 nautical miles. Two patients died during search and rescue missions. All patient are hospitalized. CONCLUSION: Ambulance and search and rescue mission near the western coasting of the French Britain are a challenge. Using a heavy helicopter from French Navy was the best way to carry medical treatment to seafarers and passengers of ferries suffering from acute heart disease