04 Jan 2023
 | 04 Jan 2023
Status: this preprint is currently under review for the journal TC.

Assimilating CryoSat-2 freeboard to improve Arctic sea ice thickness estimates

Imke Sievers, Till A. S. Rasmussen, and Lars Stenseng

Abstract. In this study, a new method to assimilate satellite radar altimetry derived freeboard instead of sea ice thickness is presented with the goal of improving the initial state of sea ice thickness predictions in the Arctic. In order to quantify the improvement in sea ice thickness gained by assimilating freeboard, we compare three different model runs. One reference run (refRun), one that assimilates only SIC (sicRun) and one that assimilates both SIC and FB (fbRun). It is shown that, estimates for both SIC and FB can be improved by assimilation, but only the fbRun improved the sea ice thickness estimates. The resulting sea ice thickness is evaluated by comparing it to Alfred Wegener Institute's (AWI) weekly CryoSat-2 sea ice thickness data product, which is based on the same FB observations as were assimilated in this study. It is shown that the sea ice thickness from the fbRun is closer to the traditional CryoSat-2 sea ice thickness than sea ice thickness from refRun or sicRun. Additionally, we compare independent sea ice draft measurements from the Beaufort Gyre Exploration Project to both fbRun sea ice thickness and observed CryoSat-2 sea ice thickness. This comparison shows that our new method provides equally good results as the AWI weekly CryoSat-2 product; in two of three locations even better results.

Imke Sievers 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-2022-262', Anonymous Referee #1, 31 Jan 2023
    • AC1: 'Reply on RC1', Imke Sievers, 20 Mar 2023
  • RC2: 'Comment on tc-2022-262', Anonymous Referee #2, 13 Feb 2023
    • AC2: 'Reply on RC2', Imke Sievers, 20 Mar 2023

Imke Sievers et al.

Imke Sievers et al.


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Short summary
The polar orbiting satellite CryoSat-2 measures freeboard, which is used to derive sea ice thickness (SIT). This SIT comes with large uncertainties due to uncertainties in sea ice density, snow density and snow thickness. This study presents a method to derive SIT by assimilating the freeboard into the sea ice model CICE. It is shown that the SIT from freeboard assimilation gives comparable results as SIT derived from classical approach and mooring based sea ice draft measurements.