08 Mar 2022
08 Mar 2022
Status: this preprint is currently under review for the journal TC.

Evaluating Greenland Surface-Mass-Balance and Firn-Densification Data Using ICESat-2 Altimetry

Benjamin E. Smith1, Brooke Medley2, Xavier Fettweis3, Tyler Sutterley1, Patrick Alexander4,5, David Porter4, and Marco Tedesco4,5 Benjamin E. Smith et al.
  • 1University of Washington Applied Physics Laboratory Polar Science Center, Seattle, WA, 98122, USA
  • 2Cryospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
  • 3SPHERES research unit, Geography, University of Liège, Liège, Belgium
  • 4Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
  • 5NASA Goddard Institute for Space Studies, New York, NY 10025, USA

Abstract. Surface-mass-balance (SMB) and firn-densification (FD) models are widely used in altimetry studies as a tool to separate atmospheric-driven from ice-dynamics-driven ice-sheet mass changes, and to partition observed volume changes into ice-mass changes and firn-air-content changes. Until now, SMB models have been principally validated based on comparison with ice core and weather-station data, or comparison with widely separated flight radar-survey flight lines. Firn-densification models have been primarily validated based on their ability to match net densification over decades, as recorded in firn cores, and the short-term time-dependent component of densification has rarely been evaluated at all. The advent of systematic ice-sheet-wide repeated ice-surface-height measurements from ICESat-2 (the Ice Cloud, and land Elevation Satellite, 2) allows us to measure the net surface-height change of the Greenland ice sheet at quarterly resolution, and compare the surface height changes directly with those predicted by three FD/SMB models. By segregating the data by season and elevation, and based on the timing and magnitude of modelled processes in areas where we expect minimal ice-dynamic-driven height changes, we investigate the models’ accuracy in predicting atmospherically-driven height changes. We find that while all three models do well in predicting the large seasonal changes in the low-elevation parts of the ice sheet where melt rates are highest, two models systematically overpredict, by around a factor of two, the magnitude of height changes in the high-elevation parts of the ice sheet, particularly those associated with melt events. This overprediction seems to be associated with the melt sensitivity of the models in the high-elevation part of the ice sheet, and third model, which has an updated high-elevation melt parameterization, avoids this overprediction.

Benjamin E. Smith et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2022-44', Anonymous Referee #1, 04 May 2022
    • AC1: 'Reply on RC1', Benjamin Smith, 07 Sep 2022
  • RC2: 'Review of Smith et al. (tc-2022-44)', Anonymous Referee #2, 02 Jun 2022
    • AC1: 'Reply on RC1', Benjamin Smith, 07 Sep 2022
  • RC3: 'Comment on tc-2022-44', Anonymous Referee #3, 13 Jun 2022
    • AC1: 'Reply on RC1', Benjamin Smith, 07 Sep 2022

Benjamin E. Smith et al.

Benjamin E. Smith et al.


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Short summary
In this paper, we use repeated satellite measurements of the height of the Greenland to learn about how three computational models of snowfall, melt, and snow compaction represent actual changes in the ice sheet. We find that the models do a good job of estimating how the parts of the ice sheet near the coast have changed, but that two of the models have trouble representing surface melt for the highest part of the ice sheet. This work provides suggestions for how to better model snow melt.