initMIP Overview: Focus on initialization
Earlier large-scale ice sheet experiments e.g. those run during the ice2sea and SeaRISE initiatives have shown that ice sheet initialization can have a large effect on sea-level projections and gives rise to important uncertainties. Improving initialization 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 initialization technique for intercomparison (initMIP). This, we hope, allows getting modelers 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. Result of initMIP-Greenland have been published in the following article:
- Goelzer, H.’, Nowicki, S., Edwards, T., Beckley, M., Abe-Ouchi, A., Aschwanden, A., Calov, R., Gagliardini, O., Gillet-Chaulet, F., Golledge, N. R., Gregory, J., Greve, R., Humbert, A., Huybrechts, P., Kennedy, J. H., Larour, E., Lipscomb, W. H., Le clec’h, S., Lee, V., Morlighem, M., Pattyn, F., Payne, A. J., Rodehacke, C., Rückamp, M., Saito, F., Schlegel, N., Seroussi, H., Shepherd, A., Sun, S., van de Wal, R., and Ziemen, F. A. (2018). Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison, The Cryosphere, 12, 1433-1460, doi:10.5194/tc-12-1433-2018.
- The model output and forcing data is available in a public archive: Results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison, doi:10.5281/zenodo.1173088
- Compare and evaluate the initialization methods used in the ice sheet modeling community
- Estimate uncertainty associated with initialization
- Get the ice sheet modeling community started with ISMIP6 activities
- Document on-going model development, as the simple experiments could be repeated with new model versions
initMIP Greenland 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 three schematic forward experiments:
init: Initialization to present day with method of choice
- 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 initialization in terms of model drift (
2a. ctrl) and response to a large perturbation (
2b. asmb). For
2a. ctrl, 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. asmb consists of a given surface mass balance anomaly, which has to be applied relative to the initial SMB inherent to the individual initialization technique. The SMB anomaly in
2b. asmb (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 initialization method
- 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 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 through the ISMIP6 datasets distributed via the Ghub Globus web application. See the instructions document at the end of this wiki. Modeling groups should use the 1km version to conservatively interpolate to their model native grid (see Appendix 1, below). Files of lower resolution (5 km, 10 km, and 20 km) are provided for groups using the output grid (Bamber et al., 2001) as “native grid”. For `2b. asmb’ as, 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
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/m3 and 31,556,926 s/yr.
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 70° N and a central meridian of 45° W (315° E) on datum WGS84 (EPSG3413 projection). The lower left cell center is at (-720,000 m,-3,450,000 m) with nx=1,681 and ny=2,881 cells in x and y-direction at full km positions (xmin = -720 km, xmax = +960 km, ymin = -3,450 km, ymax = -570 km). 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 to your native grid, and transform your model variables to the initMIP output grid (20 km, 10 km, 5 km, 2 km, 1 km), 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.
Note: The previously requested regular grid was in 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 (-800,000 m, -3,400,000 m) and the upper right at (700,000 m, -600,000 m). This is the same grid (Bamber et al., 2001) used to provide the SMB anomaly forcing previously. This grid was changed to the EPSG3413 projection described above.
A1.1 Regridding Tools and Tips
- An overview of the regridding process can be found on the two Regridding pages below.
- Regridding with CDO contains tools and tips that have been used by ISMIP6 members
- Regridding BISICLES output with ESMF and NCO contains other tools and tips
- ISMIP6 is designing tools to help with the regridding.
- If you need help with conservative interpolation, please email firstname.lastname@example.org.
Appendix 2 – Naming conventions, upload and model output dataPlease 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:
File name convention for scalar variables:
File name convention for readme file:
<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:
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 Accessing ISMIP6 datasets and submitting model experiments to Globus
ISMIP6 datasets are distributed via the Ghub Globus web application. Public datasets can be found in Ghub’s Browse Data page. ISMIP6-specific initMIP Antarctic (and initMIP Greenland and projection data) can be accessed through the Ghub endpoints via Globus UI. To access and download data, one must create a Ghub account and register with Globus. Instructions to create accounts can be referenced in the General ISMIP6 Globus Instructions (v. 2023) instruction document at the end of this wiki.
The document provides instructions on how to use Globus to download Ghub data in general, including the ISMIP6 datasets distributed via Ghub. These datasets are from earlier ISMIP6 activities, such as the initMIP, ABUMIP or projections to 2100. ISMIP6 and GHub is partnered with UB CCR to provide access to large datasets. These datasets are described in detail on our Browse Data page. If you have any questions or issues, please contact us by email at ismip6-at-gmail.com. Please also check the suggested text to acknowledge the many scientists and organizations that made the ISMIP6 data possible.
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.
|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_ice_sheet_area||m2||spatial integration|
|Floating ice area||t||ST||iareaf||floating_ice_shelf_area||m2||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
|Model ID||Numerics||Ice Flow||Initialization||Initial Year||Initial SMB||Velocity||Bed||Surface||GHF||Res min||Res max|
|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|
|Basal sliding:||PL=Pseudo-plastic, NP=Nearly Plastic, VS= Viscous Sliding, WS= Weertman Sliding|
|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.|
|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, Arctic and Climate, 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, Thomas Reerink||IMAUICE||IMAU||Utrecht University, Institute for Marine and Atmospheric Research (IMAU), Utrecht, NL|
|Nicole Schlegel, Helene Seroussi||ISSM||JPL||NASA Jet Propulsion Laboratory, Pasadena, USA|
|William Lipscomb, Joseph H. Kennedy||CISM||LANL||National Center for Atmospheric Research, Boulder, CO, 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, Frank Pattyn||FETISH||ULB||Laboratoire de Glaciologie, Université Libre de Bruxelles, Brussels, BE|
|Philippe Huybrechts, Heiko Goelzer||GISM||VUB||Vrije Universiteit Brussel, Brussels, BE|
General ISMIP6 Globus Instructions (v. 2023): Globus_Instructions_ismip6_general_June2023.docx (2 MB, uploaded by Katelyn Eaman 2 months 4 weeks ago).
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).