Abstract
Abstract. The shallow ice approximation (SIA) is commonly used in ice-sheet models to simplify the force balance equations within the ice. However, the SIA cannot adequately reproduce the dynamics of the fast flowing ice streams usually found at the margins of ice sheets. To overcome this limitation, recent studies have introduced heuristic hybrid combinations of the SIA and the shelfy stream approximation. Here, we implement four different hybrid schemes into a model of the Antarctic Ice Sheet in order to compare their performance under present-day conditions. For each scheme, the model is calibrated using an iterative technique to infer the spatial variability in basal sliding parameters. Model results are validated against topographic and velocity data. Our analysis shows that the iterative technique compensates for the differences between the schemes, producing similar ice-sheet configurations through quantitatively different results of the sliding coefficient calibration. Despite this we observe a robust agreement in the reconstructed patterns of basal sliding parameters. We exchange the calibrated sliding parameter distributions between the schemes to demonstrate that the results of the model calibration cannot be straightforwardly transferred to models based on different approximations of ice dynamics. However, easily adaptable calibration techniques for the potential distribution of basal sliding coefficients can be implemented into ice models to overcome such incompatibility, as shown in this study.
Highlights
Accurate projections of ice-sheet-driven sea level changes require the use of numerical models that are capable of capturing the dynamics of rapidly flowing regions and groundingline zones (Pattyn et al, 2013)
In this chapter we present an ensemble of simulations of the Antarctic Ice Sheet (AIS) aiming to comprehensively evaluate different hybrid schemes combining the shallow ice approximation (SIA) and SStA
Keeping in mind that each hybrid scheme builds upon the SIA solution, partially or entirely replacing it at variable locations with the SStA solution, we have included the results from the SIA-only scheme in our comparison
Summary
Accurate projections of ice-sheet-driven sea level changes require the use of numerical models that are capable of capturing the dynamics of rapidly flowing regions and groundingline zones (Pattyn et al, 2013). This requirement can be best accommodated using the most complete models currently available for modelling the ice dynamics, referred to as full Stokes (FS) models The timescales over which an ice sheet builds up and disintegrates in response to variations in the climatic forcing typically involve many thousands of years Numerical experiments over such time spans are necessary to separate the long-term transient component from relatively fast fluctuations in the ice volume during the observational record.
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