InitMIP-Greenland

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Overview

Earlier large-scale Greenland ice sheet experiments e.g. those run during ice2sea and SeaRISE initiatives have shown that ice sheet initialisation can have a large effect on sea-level projections and gives rise to important uncertainties. Improving initialisation techniques is currently a field of active research, which makes it difficult to prescribe one technique as the method of choice for ISMIP6. Instead, we first propose a “Come as you are”- approach, which allows participants to contribute with their currently used model setup and initialisation technique for intercomparison (initMIP). This, we hope, allows getting modellers involved early in the ISMIP6 process and keeps the workload for participants as low as possible. Furthermore, the proposed schematic experiments may facilitate to document on-going model development. Starting early in the CMIP6 process implies relying on schematic forcing for the initiation experiments that is independent from CMIP6 AOGCM output, which will only become available later on. The initMIP-Greenland is the first in a series of ISMIP6 ice sheet model intercomparison activities and is led by Heiko Goelzer.

Goals

• Compare and evaluate the initialisation methods used in the ice sheet modelling community

• Estimate uncertainty associated with initialisation

• Get the ice sheet modelling community started with ISMIP6 activities

• Document on-going model development, as the simple experiments could be repeated with new model versions

Experimental setup

Experiments are for the large scale Greenland ice sheet and are designed to allow intercomparison between models of 1) the initial state itself and 2) the response in two schematic forward experiments:

1. init: Initialisation to present day with method of choice

2. Schematic forward experiments

2a. ctrl: Unforced control run (100 years)

2b. asmb: Prescribed schematic surface mass balance anomaly (100 years)

The two forward experiments serve to evaluate the initialisation in terms of model drift (2a, ctrl) and response to a large perturbation (2b, asmb). For 2a, the models are run forward without any anomaly forcing, such that whatever surface mass balance (SMB) was used in the initialization technique would continue unchanged. The perturbation in 2b consists of a given surface mass balance anomaly, which has to be applied relative to the initial SMB inherent to the individual initialisation technique. The SMB anomaly in 2b (the same for each model) is schematic and should not be considered as a realistic projection. The core experiment duration is set to 100 years.

Requirements for the experiments

• Participants can and are encouraged to contribute with different models and/or initialisation methods

• Models have to be able to prescribe a given SMB anomaly

• No adjustment of SMB due to geometric changes in forward experiments (i.e. no elevation – SMB feedback is allowed)

• No bedrock adjustment in forward experiment

• The choice of model input data is unconstrained to allow participants the use of their preferred model setup without modification. Modelers without preferred data set choice can have a look at the ISMIP6 Datasets page for possible options

• The specific year of initialization (between 1950 and 2014) is equally unconstrained to allow the use of different observational data sets that may be tied to certain time periods.

Prescribed SMB anomaly

The SMB anomaly can be obtained via the ISMIP6 ftp server (email ismip6@gmail.com to obtain the login information). Modeling groups should use the 1km version to conservatively interpolate to their model native grid (see Appendix 1, below). Files of lower resolution (5km, 10km, and 20km) are provided for groups using the output grid (Bamber et al., 2001) as “native grid”. For 2b, the amplitude of the SMB anomaly is to be implemented as a time dependent function, which increases step-wise every full year (it is therefore independent of the time step in the model):


SMB(t) = SMB_initialization + SMB_anomaly * (floor (t) / 40); for 0 < t < 40 in years

SMB(t) = SMB_initialization + SMB_anomaly * 1.0; for t > 40 years


where SMB_anomaly is the anomaly provided by ISMIP6 and SMB_initialization is the model specific SMB used for the initialization. The units of SMB_anomaly are (meter ice equivalent/year) with an assumed density of 910 kg/m^3 and 31556926 s/yr.

Specific uncertainty analysis

At a later stage and informed by the diversity and similarities of participating models, ISMIP6 will suggest further experiments to explicitly address certain aspects of uncertainty in the initialisation. It is hoped that participating groups will contribute to these additional experiments, which apply specific perturbations to the initialisations. These would take the form of repeating the experiments with systematic perturbations of the initialization choices, for example:

– Boundary conditions and other datasets

– Parameters

– Model structure

– Methods and judgments, e.g. tolerance for data mismatch or drift

- ...

References

Bamber, J. L., Layberry, R. L., and Gogineni, S.: A new ice thickness and bed data set for the Greenland ice sheet 1. Measurement, data reduction, and errors, J. Geophys. Res.-Atmos., 106, 33773–33780 (2001).

Bamber, J.L., Griggs, J.A., Hurkmans, R.T.W.L., Dowdeswell, J. A., Gogineni, S. P., Howat, I., Mouginot, J., Paden, J., Palmer, S., Rignot, E., and Steinhage, D.: A new bed elevation dataset for Greenland. Cryosphere 7, 499–510 (2013).

Appendix 1 – Output grid definition and interpolation

All 2D data is requested on a regular grid with the following description. Polar stereo-graphic projection with standard parallel at 71° N and a central meridian of 39° W (321° E) on datum WGS84. The lower left corner is at (-800000 m, -3400000 m) and the upper right at (700000 m, -600000 m). This is the same grid (Bamber et al., 2001) used to provide the SMB anomaly forcing. The output should be submitted on a resolution adapted to the resolution of the model and can be 20 km, 10 km, 5 km, 2 km or 1 km. The data will be conservatively interpolated to 1 km resolution for archiving and 5 km resolution for diagnostic processing by ISMIP6.

If interpolation is required in order to transform the SMB forcing (1km, same as Bamber et al. 2013) to your native grid, and transform your model variables to the initMIP output grid (20 km, 10 km, 5 km, 2 km, 1 km, Bamber et al. 2001), it is required that conservative interpolation is used. The motivation for using a common method for all models is to minimize model to model differences due to the choice of interpolation method.

A1.1 Regridding Tools and Tips

  • An overview of the regridding process can be found on the Regridding page.
  • Regridding_with_CDO contains tools and tips that have been used by ISMIP6 members

Appendix 2 – Naming conventions, upload and model output data.

Please provide:

• one variable per file for all 2D fields

• all variables in one file for the scalar variables

• a completed readme file

A2.1 File name convention

File name convention for 2D fields:

<variable>_<IS>_<GROUP>_<MODEL>_<EXP>.nc

File name convention for scalar variables:

scalar_<IS>_<GROUP>_<MODEL>_<EXP>.nc

File name convention for readme file:

README_<IS>_<GROUP>_<MODEL>.doc

where

<variable> = netcdf variable name (e.g. lithk)

<IS> = ice sheet (AIS or GIS)

<GROUP> = group acronym (all upper case or numbers, no special characters)

<MODEL> = model acronym (all upper case or numbers, no special characters)

<EXP> = experiment name (init, ctrl or asmb)

For example, a file containing the scalar variables for the Greenland ice sheet, submitted by group “JPL” with model “ISSM” for experiment “ctrl” would be called: scalar_GIS_JPL_ISSM_ctrl.nc

If JPL repeats the experiments with a different version of the model (for example, by changing the sliding law), it could be named ISSM2, and so forth.

A2.2 Uploading your model output

Please upload your model output on the FTP server cryoftp1.gsfc.nasa.gov, and email ismip6@gmail.com for the user name and latest password. Note sftp does not work!

After log in, go to the ISMIP6/initMIP/output directory via:

ftp> cd /ISMIP6/initMIP/output

and create a directory named <GROUP> with the following sub-directory structure:

initMIP output/ <GROUP>/ <MODEL>/ init/ ctrl/ asmb/

Create additional <MODEL> directories when participating with more than one model or model version.

An example of model output files can be found in /ISMIP6/initMIP/output/ISMIP6/REF.

A2.3 Model output variables and README file

The README file is an important contribution to the initMIP submission. It may be obtained here or requested by email to ismip6-at-gmail.com


The variables requested in the table below serve to evaluate and compare the different models and initialization techniques. Some of the variables may not be applicable for your model, in which case they are to be omitted (with explanation in the README file). Also, specify missing values in your netcdf file where needed, and fields should be undefined outside of the ice mask.

We distinguish between state variables (e.g. ice thickness, temperatures and velocities) and flux variables (e.g. SMB). Flux variables are defined as positive when the process adds mass to the ice sheet and negative otherwise. Note the different treatment for state variables (snapshots) and fluxes (time average). The standard should be averaging over all native time steps for yearly scalar output and for 5 year periods for 2D fields. Please specify how your reported flux data has been averaged over time in the README file.

Example model output files can be found in /ISMIP6/initMIP/output/ISMIP6/REF on the ftp server.

Variable Dim Type Variable Name Standard Name Units Comment
2D variables requested every five years, starting at t=0, snapshots for type ST and as five year average for type FL
Ice thickness x,y,t ST lithk land_ice_thickness m The thickness of the ice sheet
Surface elevation x,y,t ST orog surface_altitude m The altitude or surface elevation of the ice sheet
Bedrock elevation x,y,t ST topg bedrock_altitude m The bedrock topography (unchanged in forward exps.)
Geothermal heat flux x,y C hfgeoubed upward_geothermal_heat_flux_at_ground_level W m-2 Geothermal Heat flux (unchanged in forward exps.)
Surface mass balance flux x,y,t FL acabf land_ice_surface_specific_mass_balance_flux kg m-2 s-1 Surface Mass Balance flux (for areas covered by ice only)
Basal mass balance flux x,y,t FL libmassbf land_ice_basal_specific_mass_balance_flux kg m-2 s-1 Basal mass balance flux (for areas covered by ice only)
Ice thickness imbalance x,y,t FL dlithkdt tendency_of_land_ice_thickness m s-1 dHdt
Surface velocity in x x,y,t ST uvelsurf land_ice_surface_x_velocity m s-1 u-velocity at land ice surface
Surface velocity in y x,y,t ST vvelsurf land_ice_surface_y_velocity m s-1 v-velocity at land ice surface
Surface velocity in z x,y,t ST wvelsurf land_ice_surface_upward_velocity m s-1 w-velocity at land ice surface
Basal velocity in x x,y,t ST uvelbase land_ice_basal_x_velocity m s-1 u-velocity at land ice base
Basal velocity in y x,y,t ST vvelbase land_ice_basal_y_velocity m s-1 v-velocity at land ice base
Basal velocity in z x,y,t ST wvelbase land_ice_basal_upward_velocity m s-1 w-velocity at land ice base
Mean velocity in x x,y,t ST uvelmean land_ice_vertical_mean_x_velocity m s-1 The vertical mean land ice velocity is the average from the bedrock to the surface of the ice
Mean velocity in y x,y,t ST vvelmean land_ice_vertical_mean_y_velocity m s-1 The vertical mean land ice velocity is the average from the bedrock to the surface of the ice
Surface temperature x,y,t ST litempsnic temperature_at_ground_level_in_snow_or_firn K Ice temperature at surface
Basal temperature x,y,t ST litempbot land_ice_basal_temperature K Ice temperature at base
Basal drag x,y,t ST strbasemag magnitude_of_land_ice_basal_drag Pa Magnitude of basal drag
Calving flux x,y,t FL licalvf land_ice_specific_mass_flux_due_to_calving kg m-2 s-1 Loss of ice mass resulting from iceberg calving. Only for grid cells in contact with ocean
Land ice area fraction x,y,t ST sftgif land_ice_area_fraction 1 Fraction of grid cell covered by land ice (ice sheet, ice shelf, ice cap, glacier)
Grounded ice sheet area fraction x,y,t ST sftgrf grounded_ice_sheet_area_fraction 1 Fraction of grid cell covered by grounded ice sheet, where grounded indicates that the quantity correspond to the ice sheet that flows over bedrock
Floating ice sheet area fraction x,y,t ST sftflf floating_ice_sheet_area_fraction 1 Fraction of grid cell covered by ice sheet flowing over seawater
Scalar outputs requested every full year, as snapshots for type ST as 1 year averages for type FL. The t=0 value should contain the data of the initialization.
Total ice mass t ST lim land_ice_mass kg spatial integration, volume times density
Mass above floatation t ST limnsw land_ice_mass_not_displacing_sea_water kg spatial integration, volume times density
Grounded ice area t ST iareag grounded_land_ice_area m^2 spatial integration
Floating ice area t ST iareaf floating_ice_shelf_area m^2 spatial integration
Total SMB flux t FL tendacabf tendency_of_land_ice_mass_due_to_surface_mass_balance kg s-1 spatial integration
Total BMB flux t FL tendlibmassbf tendency_of_land_ice_mass_due_to_basal_mass_balance kg s-1 spatial integration
Total calving flux t FL tendlicalvf tendency_of_land_ice_mass_due_to_calving kg s-1 spatial integration

Appendix 3 – Participating Models and Characteristics

Greenland Standalone Ice Sheet Modeling

Contributors Model Group ID Group
Nick Golledge PISM ARC Antarctic Research Centre, Victoria University of Wellington, NZ
Martin Rückamp, Angelika Humbert ISSM AWI Alfred Wegener Institute for Polar and Marine Research, DE /University of Bremen, DE
Victoria Lee, Tony Payne BISICLES BGC University of Bristol, Bristol, UK
Christian Rodehacke PISM DMI Danish Meteorological Institute, DK
Ralf Greve SICOPOLIS ILTS Institute of Low Temperature Science, Hokkaido University, Sapporo, JP
Ralf Greve, Reinhard Calov SICOPOLIS ILTS_PIK Institute of Low Temperature Science, Hokkaido University, Sapporo, JP /

Potsdam Institute for Climate Impact Research, Potsdam, DE

Heiko Goelzer, Roderik van de Wal IMAUICE IMAU Utrecht University, Institute for Marine and Atmospheric Research (IMAU), Utrecht, NL
Helene Seroussi, Nicole Schlegel ISSM JPL NASA Jet Propulsion Laboratory, Pasadena, USA
William Lipscomb, Joseph H. Kennedy CISM LANL Los Alamos National Laboratory, Los Alamos, USA / Oak Ridge National Laboratory, USA
Fabien Gillet-Chaulet, Olivier Gagliardini Elmer LGGE Laboratoire de Glaciologie et Géophysique de l'Environnement, FR
Sébastien Le clec'h GRISLI LSCE Laboratoire des sciences du climat et de l'environnement, FR
Fuyuki Saito, Ayako Abe-Ouchi IcIES MIROC Japan Agency for Marine-Earth Science and Technology, JP / The University of Tokyo, Tokyo, JP
Florian Ziemen PISM MPIM Max Planck Institute for Meteorology, DE
Andy Aschwanden PISM UAF Geophysical Institute, University of Alaska Fairbanks, USA
Helene Seroussi, Mathieu Morlighem ISSM UCIJPL NASA Jet Propulsion Laboratory, Pasadena, USA / University of California Irvine, Irvine, USA
Sainan Sun and Frank Pattyn FETISH ULB Laboratoire de Glaciologie, Université Libre de Bruxelles, Brussels, BE
Philippe Huybrechts, Heiko Goelzer GISM VUB Vrije Universiteit Brussel, Brussels, BE

Model Characteristics

Model ID Numerics Ice Flow Initialization Initial Year Initial SMB Velocity Bed Surface GHF Res min Res max
ARC-PISM FD HYB SP 2000 RA1 B SR 5 5
AWI-ISSM1 FE HO DE 2000 RA3 RM M SR 2.5 35
AWI-ISSM2 FE HO DE 2000 RA3 RM M SR 2.5 35
BGC-BISICLES1 FV SSA DE 1997-2006 HIR RM M 1.2 4.8
BGC-BISICLES2 FV SSA DE 1997-2006 HIR RM M 2.4 4.8
BGC-BISICLES3 FV SSA DE 1997-2006 HIR RM M 4.8 4.8
DMI-PISM1 FD HYB SP 2000 PDD B SR 5 5
DMI-PISM2 FD HYB SP 2000 PDD B SR 5 5
DMI-PISM3 FD HYB SP 2000 PDD B SR 5 5
DMI-PISM4 FD HYB SP 2000 PDD B SR 5 5
DMI-PISM5 FD HYB SP 2000 PDD B SR 5 5
ILTS-SICOPOLIS FD SIA SP 1990 PDD B P 5 5
ILTSPIK-SICOPOLIS FD SIA SP 1990 PDD H G 5 5
IMAU-IMAUICE1 FD SIA SP 1990 RA3 B SR 5 5
IMAU-IMAUICE2 FD SIA SP 1990 RA3 B SR 10 10
IMAU-IMAUICE3 FD SIA SP 1990 RA3 B SR 20 20
JPL-ISSM FE SSA DA 2012 BOX RM M SR 1 15
LANL-CISM FE HO SP 1961-1990 RA1 M CTE 4 4
LGGE-ELMER1 FE SSA DA 2000-2010 MAR J M 1.5 45
LGGE-ELMER2 FE SSA DA 2000-2010 MAR J M 1 5
LSCE-GRISLI FD HYB DA 2000 MAR J M FM 5 5
MIROC-ICIES1 FD SIA DA 2004 RA1 B B 10 10
MIROC-ICIES2 FD SIA SP 2004 PDD B 10 10
MPIM-PISM FD HYB SP 2006 PDD B 5 5
UAF-PISM1 FD HYB SP 2007 RA1 M SR 1.5 1.5
UAF-PISM2 FD HYB SP 2007 RA1 M SR 3 3
UAF-PISM3 FD HYB SP 2007 RA1 M SR 4.5 4.5
UAF-PISM4 FD HYB SP 2007 RA1 M SR 1 1
UAF-PISM5 FD HYB SP 2007 RA1 M SR 3 3
UAF-PISM6 FD HYB SP 2007 RA1 M SR 4.5 4.5
UCIJPL-ISSM FE HO DE 2007 RA1 RM M SR 0.5 30
ULB-FETISH1 FD HYB DA 1979-2006 PDD B B FM 10 10
ULB-FETISH2 FD HYB DA 1979-2006 PDD B B FM 10 10
VUB-GISM1 FD HO SP 2005 PDD B SR 5 5
VUB-GISM2 FD SIA SP 2005 PDD B SR 5 5

Numerical method: FD= Finite difference, FE= Finite element, FV= Adaptive mesh refinement

Ice flow: SIA= Shallow ice approximation, SSA= Shallow shelf approximation, HO= Higher order, HYB= Hybrid SIA-SSA

Initialization: DA= Data Assimilation, SP= Spin up

Initial SMB: RA1= RACMO2.1, RA3= RACMO2.3, HIR=HIRHAM5, PDD= Positive Degree Day Model, MAR= MAR, BOX=BOX reconstruction

Velocity: RM= Rignot and Mouginot, J= Joughin et al.

Bed and surface: M= Morlinghem et al., B= Bamber et al., H=Herzfeld

Geothermal Heat Flux (GHF): SR= Shapiro and Ritzwoller, G= Greve, P= Purucker, FM= Fox Maule et al.,

Model resolution (Res) in km. In case of heterogeneous grid resolution the minimum and maximum resolution are given.

Initial Results