Modeling Tides for Southern Ocean GLOBEC

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Modeling Tides for Southern Ocean GLOBEC

• Susan Howard and Laurence Padman
• Earth Space Research

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Motivation

• Tidal currents are noise in ship ADCP records.
  A model helps us remove them to highlight the
  mean circulation.
• Tides contribute to benthic stirring and
  pycnocline mixing.
• Ocean-applied stresses on the sea-ice base affect
  ice kinematics and surface buoyancy exchanges.

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Topics

• 2-D model
• Description of model
• Results
• Validation
• 3-D model (preliminary work)
• Description of model
• Results

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2-D Model CATS

• Resolution The resolution is 1/4o E/W and 1/12o
  N/S (10 km at 70oS).
• Forced by height fields along 58oS obtained from
  the Oregon State University TPXO5.1 global tidal
  solution.

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CATS

• Model
• Domain

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2-D Model CATS

• Resolution The resolution is 1/4o E/W and 1/12o
  N/S (10 km at 70oS).
• Forced by height fields along 58oS obtained from
  the Oregon State University TPXO5.1 global tidal
  solution.
• Bathymetry modified ETOPO-5.
• Constituents K1,O1,P1,Q1, M2,S2,N2,K2,Mm,Mf.

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K1
M2
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CATS Model

• Mean tidal speed
• 10 Constituents
• Weak tides except at shelf break
• Tides at shelf break diurnal (TVW)
• Currents will be affected by bathymetry

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Tidal Signal in Drifters

• Max speeds
• 15 cm s-1
• Diurnal band
• only
• Speed varies
• with position
• spring neap cycle
• Evidence of
• strong tides near
• shelf break

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CATS vs. Moorings
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3-D Model POM

• Resolution The resolution is 1/8o E/W and 1/15o
  N/S (8 km).
• (we want to work toward a 2-4 km res.)
• Forced by normal flow at open boundaries (taken
  from CATS).

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POM
Model Domain (preliminary)
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3-D Model POM

• Resolution The resolution is 1/8o E/W and 1/15o
  N/S (8 km).
• Forced by normal flow at open boundaries (taken
  from CATS).
• Bathymetry modified ETOPO5.
• Constituents K1 and M2, modeled separately.

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K1
K1
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M2
Adelaide Island
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K1
Adelaide Island
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M2
Adelaide Island
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M2
M2
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Conclusions

• Tidal currents are quite weak except at the shelf
  break.
• Internal tides may be generated by both diurnal
  and semidiurnal flows across the upper
  continental slope.
• Surface tidal currents move the ice pack around,
  and may also increase open-water fraction.
• Lots of room for model improvements!

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CATS Model Improvements

• Rerun Cats with New WHOI Bathymetry
• Improve resolution
• Update internal tide dissipation parameterization
• Assimilate BPR and coastal tide gauge data

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POM Model Improvements

• Use new WHOI bathymetry
• Increase resolution
• Increase domain size
• Use spatially varying stratification
• Examine seasonal effects of stratification
• Improve open boundary conditions

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Acknowledgements

• We would like to thank Dick Limeburner
• for providing us with drifter data and Lana
• Erofeeva for help with tide modeling.