An Ocean Tidal Inverse Model

1
An Ocean Tidal Inverse Model For Antarctic Ice
Shelves Application to Amery Ice Shelf
Laurie Padman Helen A. Fricker Richard Coleman
2
Why Study Tides?

• Remove tide signals from satellite (InSAR,
  altimetry) and in situ (GPS, gravity, tilt) data
• Tides influence

• Ice shelf basal melting and refreezing
• Iceberg calving and subsequent drift
• Ocean mixing (water mass modification)
• and sea ice distribution

3
Standard Deviation of Tide Height
Amery
CADA00.10
RMS Tide Height (cm) Hmax ? 4RMS
4
Tide Model Choices

• Empirical data analyses
• Dynamical momentum equations
• ?Assimilation formalized hybrid
• Assimilation nudges dynamical
• solution towards better fit with data

5
The Inverse Model (CADA)

• Circum-Antarctic, 86o-58oS, 10 km grid spacing
• Oregon State Tidal Inversion Software (G. Egbert)
• Bathymetry includes water column thickness
  under major ice shelves

6
Potential Data Sources

• ? TOPEX/Poseidon radar altimetry
• ? Tide gauges (coastal, benthic) (30)
• ? GPS on ice shelves (1 only)
• ? Gravimeter (Ross 10)
• ERS-1 ERS-2 radar altimetry
• Future laser altimetry (GLAS on
• ICESat)

7
Amery Ice Shelf
Dynamics-only With Assimilation


M2 Amplitude (cm)
8
Model Comparisons, Southern Amery
Forward Assimilation Difference
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Satellite Aliasing Problem
TOPEX/Poseidon ERS 35-day
10
ERS Altimeter Tide Measurements
G1 (near ice front)
?t?2.4 days
CADA00.10
?Hmodel80.8?HERS
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Summary

• Optimistic outlook for tide prediction with data
  assimilation
• Useful data for model upgrades include

• Satellite altimetry (ERS, GLAS)
• Better open-ocean bathymetry grid
• Ice shelf grounding lines (InSAR)
• Ice shelf GPS
• Sub-ice water column thickness (ground-
• based radar)