Parameter and state estimation with a time-dependent adjoint marine ice sheet model
To date, assimilation of observations into large-scale ice models has consisted predominantly of time-independent inversions of surface velocities for basal traction, bed elevation, or ice stiffness, and has relied primarily on analytically derived adjoints of glaciological stress balance models. To...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-11-01
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| Series: | The Cryosphere |
| Online Access: | http://www.the-cryosphere.net/7/1659/2013/tc-7-1659-2013.pdf |
| Summary: | To date, assimilation of observations into large-scale ice models has
consisted predominantly of time-independent inversions of surface velocities
for basal traction, bed elevation, or ice stiffness, and has relied primarily
on analytically derived adjoints of glaciological stress balance models. To
overcome limitations of such "snapshot" inversions – i.e., their inability to
assimilate time-dependent data for the purpose of constraining transient flow
states, or to produce initial states with minimum artificial drift and
suitable for time-dependent simulations – we have developed an adjoint of a
time-dependent parallel glaciological flow model. The model implements a
hybrid shallow shelf–shallow ice stress balance, solves the continuity
equation for ice thickness evolution, and can represent the floating,
fast-sliding, and frozen bed regimes of a marine ice sheet. The adjoint is
generated by a combination of analytic methods and the use of algorithmic
differentiation (AD) software. Several experiments are carried out with
idealized geometries and synthetic observations, including inversion of
time-dependent surface elevations for past thicknesses, and simultaneous
retrieval of basal traction and topography from surface data. Flexible
generation of the adjoint for a range of independent uncertain variables is
exemplified through sensitivity calculations of grounded ice volume to
changes in basal melting of floating and basal sliding of grounded ice. The
results are encouraging and suggest the feasibility, using real observations,
of improved ice sheet state estimation and comprehensive transient
sensitivity assessments. |
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| ISSN: | 1994-0416 1994-0424 |