A 2D Model for the Interleaving of Northern and Southern Atlantic Ocean Deep Waters

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A 2D Model for the Interleaving of Northern and
Southern Atlantic Ocean Deep Waters

• Guo, Xin
• October 7th 2004
• Advisor Ingersoll, Andrew P.

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Outline

• The Interleaving phenomenon in northern and
  southern Atlantic ocean deep waters
• The reason for interleaving
• The 2D model
• Results of simulation
• Conclusion and future work

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Interleaving of Atlantic Waters

• Northern Atlantic water is warmer and saltier
  than southern Atlantic water
• Atlantic source water (North Atlantic water)
  could be denser at the surface and less dense at
  the bottom than the Antarctic source water (South
  Atlantic water)
• Ingersoll 2004 suggests that the level of neutral
  buoyancy would be about 3.5km below the sea level

Hartmann, D.L., Global Physical Climatology.
International Geophysics Series, ed. R. Dmowska
and J.R. Holton. Vol. 56. 1994, San Diego
Academic Press.
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Equation of State

• Cold Fresh Water (CFW) vs Warm Salty Water (WSW)
  at different depths
• Thermobaric Effect Thermal coefficient of
  expansion increases with pressure

Hartmann, D.L., Global Physical Climatology.
International Geophysics Series, ed. R. Dmowska
and J.R. Holton. Vol. 56. 1994, San Diego
Academic Press.
Knauss, J.A., Introduction to Physical
Oceanography. 1978, New Jersey Prentice-Hall,
Inc.
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Possibility of Interleaving thermobaric effect

• At low pressure, salinity dominates density
  variance
• At high pressure, temperature dominates density
  variance
• At somewhere between, isopycnal is possible

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Observation
http//sam.ucsd.edu/vertical_sections/
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The Real Ocean
Depth1 2km North Water 1024.4438 kg/m3 South
Water 1024.3979 kg/m3 Depth2 5km North Water
1024.119 kg/m3 South Water 1024.1518 kg/m3
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The Real Ocean
Depth1 4km North Water 1024.4664 kg/m3 South
Water 1024.6752 kg/m3 Depth2 0.5km North
Water 1024.7035 kg/m3 South Water 1024.6918
kg/m3
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Model with Boussinesq Approximationequations to
solve
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Initial condition and boundary condition

• Initial conditions
• Homogenous stream function
• Homogenous potential temperature
• Homogenous salinity
• Boundary conditions
• No-slip boundaries at sides and bottom
• None-stress top boundary
• Specific salinity flux on surface
• Relaxation thermal flux
• Zero geothermal heat flux

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With Asymmetric Fluxes
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With Asymmetric Fluxes
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Conclusion and future work

• The dependence of density on various parameters
  and thermobaric effect is presented in the real
  ocean, which can explain the interleaving
• This 2D model shows its potential to reproduce
  the interleaving in thermohaline circulation
• Effects of boundary condition, initial condition
  and parameters need further exploration
• Model is simple, longitudinal circulation and sea
  floor topography could play important role

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The End
Acknowledgement
Andrew Ingersoll, Kevin Lewis, Claudia Pasquero
and Liming Li for useful guidance and discussion

• Thank you for listening

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Observation
http//sam.ucsd.edu/vertical_sections/
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With Asymmetric Fluxes
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With Asymmetric Fluxes
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With Asymmetric Fluxes
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References

• Ingersoll, A., Boussinesq and Anelastic
  Approximations Revisited Potential Energy
  Release during Thermobaric Instability. Submitted
  to Journal of Physical Oceanography, 2004.
• Hartmann, D.L., Global Physical Climatology.
  International Geophysics Series, ed. R. Dmowska
  and J.R. Holton. Vol. 56. 1994, San Diego
  Academic Press.
• Knauss, J.A., Introduction to Physical
  Oceanography. 1978, New Jersey Prentice-Hall,
  Inc.
• Vellinga, M., Instability of Two-Dimensional
  Thermohaline Circulation. Journal of Physical
  Oceanography, 1996. 26(3) p. 305-319.
• http//sam.ucsd.edu/vertical_sections/

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With symmetric fluxes
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With symmetric fluxes
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With symmetric fluxes
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With asymmetric fluxes
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With asymmetric fluxes
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Discussion on the picture of interleaving

• Thermobaric effect works
• Different levels where pole-to-pole convection
  happens
• Diffusion coefficient helps build temperature and
  salinity gradient
• Boundary fluxes and relaxation time
• Initial condition would affect the transient
  stages but not final steady stages

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Thermobaric Instability

• The dependence of density on temperature,
  salinity and pressure allows seawater to store a
  finite amount of potential energy for later
  release.

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Possibility of Interleaving thermobaric effect
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Knauss, J.A., Introduction to Physical
Oceanography. 1978, New Jersey Prentice-Hall,
Inc.
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Temperature Density
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