Comparison of adjoint and nudging methods to initialise ice sheet model basal conditions

• Published in: Geoscientific Model Development
• Main Authors: C. Mosbeux, F. Gillet-Chaulet, O. Gagliardini
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2016
• Subjects: Geology; QE1-996.5; Ice Sheet
• Online Access: https://doi.org/10.5194/gmd-9-2549-2016; https://doaj.org/article/2daeb9379f1a4fed90a8bc1cddc828eb

Ice flow models are now routinely used to forecast the ice sheets' contribution to 21st century sea-level rise. For such short term simulations, the model response is greatly affected by the initial conditions. Data assimilation algorithms have been developed to invert for the friction of the ice on its bedrock using observed surface velocities. A drawback of these methods is that remaining uncertainties, especially in the bedrock elevation, lead to non-physical ice flux divergence anomalies resulting in undesirable transient effects. In this study, we compare two different assimilation algorithms based on adjoints and nudging to constrain both bedrock friction and elevation. Using synthetic twin experiments with realistic observation errors, we show that the two algorithms lead to similar performances in reconstructing both variables and allow the flux divergence anomalies to be significantly reduced.