NOTE: This tool will be updated with a link to the hosted tool and/or source code as soon as it is available. Thank you for your patience during our transition.
The Cryosphere model Comparison tool (CmCt) compares user-uploaded ice sheet models against remote-sensing observations. Currently, the tool supports a comparison of modeled mass change against observed mass change from satellite gravimetry. The tool is also currently limited to the Greenland Ice Sheet and comparisons for the Antarctic Ice Sheet will be added shortly. In the future, the CmCt tool will also be expanded to perform comparisons of other variables such as ice sheet mass change using observations from the Ice sheet Mass Balance Inter-comparison Exercise (IMBIE), surface elevation change using laser altimetry observations, and surface velocity change using various observations.
Observational dataset description
Gravimetry
Ice sheet mass change observations are obtained from the NASA Gravity Recovery And Climate Experiment (GRACE) mission. GRACE, launched in 2002, is a dual-satellite mission with the primary objective of measuring the gravity field of the Earth as it changes over space and time (Wahr et. al., 1998). It does this by very accurately measuring the distance between the two satellites (to within a few micrometers), which are flying one behind the other in the same orbit, about 200 km apart and 400-500 km above Earth’s surface. Precisely measuring how the Earth’s gravity tugs each of the satellites differently allows for the calculation of changes in Earth’s gravitational potential field. GRACE was retired in September 2017 and a follow-on mission, GRACE-FO, was launched in May 2018 and has continued providing global mass change measurements.
The CmCt tool uses a mascon solution that was processed at NASA’s Goddard Space Flight Center (GSFC; Luthcke et al., 2013). The CmCt reprojects modeled ice sheet mass change into mascon space and performs a direct quantitative comparison, calculating model-observation discrepancies. The tool currently uses the ‘gsfc.glb_.200204_202312_rl06v2.0_obp-ice6gd.h5’ mascon product, with monthly mass change estimates over 2002 to 2023, which can be requested at the NASA GSFC dataset main distribution site. Future development of the CmCt tool will enable it to automatically check for updates to the mascon product to extend the comparison timespan.
We would like to acknowledge and thank to Michael Croteau and Bryant Loomis at NASA GSFC for providing the mascon data product and contributing to the code.
Ice sheet model data upload requirements
The CmCt gravimetry notebook expects thickness data (lithk variable) for the comparison.
At time of writing, the models MUST be defined on a rectangular X-Y grid in the ISMIP6 standard projected polar-stereographic space. (Note, NOT a lat-lon grid!) More information about ISMIP6, including information about the standard polar stereographic projection, can be found on the ISMIP6 wiki.
The mascon data range used here goes from 2002 to 2023. The desired model time range for the comparison can be set in the appropriate cells. A single file can be uploaded that includes multiple years. The start and end date range can be selected within the Jupyter notebook cells.
How to run the CmCt GRACE mascon comparison
- Set time range for comparison
- Upload ice sheet model file
- Plot observed mass change, modeled mass change, and model-observation discrepancy
Tool output
The CmCt creates a plot with the observed mass change, modeled mass change, and model-observation discrepancy. The plots can be downloaded with the Download Plot button.
Future developments for the CmCt tool
- Automated observational data product updates to extend comparison timespan
- Add Antarctica comparison
- Output quantitative comparison statistics
References
Luthcke et. al., (2013). Antarctica, Greenland and Gulf of Alaska land-ice evolution from an iterated GRACE global mascon solution, Journal of Glaciology, Vol. 59, No. 216, 2013 doi:10.3189/2013JoG12J147
Wahr et. al., (1998). Time variability of the Earth’s gravity field: Hydrological and oceanic effects and their possible detection using GRACE, Journal of Geophysical Research, Vol. 103, Issue B12, 1998 doi:10.1029/98JB02844