On the Contribution of Grain Boundary Sliding to Firn Densification – an Assessment using an Optimisation Approach
Physics based simulation approaches to firn densification often rely on the assumption that grain boundary sliding,first introduced by Alley (1987) to firn, is the leading process driving the first stage of densification. However, often so calledsemi empirical models are favored against the descript...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
| Published: |
2021
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/tc-2021-75 https://tc.copernicus.org/preprints/tc-2021-75/ |
| Summary: | Physics based simulation approaches to firn densification often rely on the assumption that grain boundary sliding,first introduced by Alley (1987) to firn, is the leading process driving the first stage of densification. However, often so calledsemi empirical models are favored against the description of grain boundary sliding due to simplicity and uncertainties regard-ing model parameters. In this study, we are assessing the applicability of grain boundary sliding to firn using a numeric firn5densification model and an optimisation approach, for which we formulate variants of the constitutive relation by Alley (1987).The efficient model implementation based on an updated Lagrangian numerical scheme enables us to perform a large numberof simulations testing different model parameters, to find simulation results suiting 159 firn density profiles from Greenlandand Antarctica best. For most of the investigated locations a good agreement of simulated and measured firn density profileswas found. This implies that the constitutive relation by Alley (1987) characterises the fist stage of firn densification well, if10suitable model parameter are used. An analysis of the parameters that lead to best matches reveals a dependency on the meansurface mass balance. This may indicate an insufficient description of the load situation, as horizontal components of the stresstensor are usually neglected in one dimensional models of the firn column. |
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