IMBIE GIA Model Intercomparison

This page describes the experimental protocol for the IMBIE GIA model inter-comparison for the IMBIE 2023 assessment. This model inter-comparison aims at (i) informing how the spread in GIA estimates contributes to the (dis)agreement between satellite-based estimates of ice sheet mass balance and (ii) understanding the sources of variations between existing GIA models to reduce uncertainties in current GIA modelled estimates.

This exercise is coordinated by Dr Karen Simon (karen.simon@nrcan-rncan.gc.ca).

Experimental Protocol

Here, we outline the experimental protocol that will be followed to analyse and compare the different GIA submissions received.

1. Comparison of Stokes coefficients

We are planning on comparing Stokes coefficients to determine the approximate magnitude of the effect of applying each correction to GRACE and GRACE-FO data.

2. Comparison of uplift rates

We will compare uplift rates and will compute the mean and standard deviation of the submissions received to identify areas of (dis)agreement between the various GIA models and assess the magnitude of those variations.

Participation Conditions

To participate in the IMBIE GIA model inter-comparison, participants are required to contribute uplift rates and Stokes coefficients using the standard format defined below. The GIA solutions must have been compared quantitatively to rebound data and must utilise an ice history model that is guided by geological constraints. To participate, participants are required to have created either the ice history or Earth model that form the basis of their GIA solution, and they may submit only one GIA estimate to this exercise for each ice sheet.

Standard data format for IMBIE 2023

We are requesting GIA participants to submit:

1. a file with uplift rates
2. a file with Stokes coefficient

We have defined standard file formats to simplify data collection and post-processing. Please only submit GIA model estimates using this format. Data submitted using other formats cannot be accepted. The file format is either a text file or netCDF for the uplift rates and a text file for the Stokes coefficients.

1. Uplift rates distributed on a 0.5 degrees grid

Please provide uplift rates distributed on a 0.5 degrees grid (Lon: 0.0, 0.5, 1.0, …, 360.0; Lat: 90.0, 89.5, 89.0,…, -90.0).

Variable	Dimension	Variable name	Standard_name	Long_name	Units	Comment
Longitude – centre	(x,y)	lon	longitude	grid centre longitude	degrees_east
Latitude – centre	(x,y)	lat	latitude	grid centre latitude	degrees_north
Uplift rates	(x,y)				mm_per_year (mm/yr)
Uncertainty of uplift rates					mm_per_year (mm/yr)	If applicable

You can find an example of a file of uplift rate here: uplift_rates_example

2. Stokes Coefficients at least up to degree and order 90

Column number	Variable
1	degree l
2	order m
3	Clm
4	Slm

You can find an example of a file of Stokes Coefficients here: Stokes_coefficients_example

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