doctoral thesis: zouhair lachkar contributors: j.-c. dutay, p. delecluse, j. c. orr lsce/ipsl,...
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Doctoral Thesis: Doctoral Thesis: Zouhair LachkarZouhair Lachkar
Contributors: Contributors: JJ..-C-C.. Dutay Dutay, , PP.. Delecluse Delecluse, J. C. Orr, J. C. Orr
LSCE/IPSL, Laboratoire des Sciences du Climat et de l’EnvironnementCEA-CNRS-UVSQ Gif-sur-Yvette, France
Towards higher resolution, Towards higher resolution, global-ocean, tracer simulationsglobal-ocean, tracer simulations
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Coarse-resolution ocean models (OCMIP-2) Large differences Generally underpredict storage
Eddy resolving global model (1/10°) 1st to give adequate Southern Extratropical CFC-11 inventory
What horizontal resolution is What horizontal resolution is needed to capture large-needed to capture large-scale distributions?scale distributions?
Background:Background:
modeldata
range of OCMIP models
Anthropogenic CO2 (1990):
Sasai et al., (2004, GRL)
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Ocean spatiotemporal scales Ocean spatiotemporal scales governing surface variabilitygoverning surface variability
Chelton et al. (2001). Satellite altimetry and earth sciences, Chap. on Satellite altimetry, 57–64. Academic Press, NY.
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Evaluate:
- eddy-induced changes in simulated tracer distributions (model vs. model)
- any improvement due to explicitly including eddies (model vs. data)?
Understand how eddies affect transient tracer uptake & storage
Explore role of mesoscale eddies in AAIW ventilation (with CFC-11 as a diagnostic tool)
Study role of eddies & temporal variability of meridional transport of heat, CFC-11, and anthropogenic CO2
Thesis work of Zouhair Thesis work of Zouhair Lachkar:Lachkar:
Part 2
Part 1
Part 3
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2 versions of same model ORCA-LIM (Madec et al., 1998;
Barnier et al., 2006)
3 transient tracers:
- CFC-11
- Anthropogenic CO2
- Bomb 14C
eddying
Eddy Kinetic Energy
Broecker and Peng, 1974
Eddy Kinetic Energy
Atmospheric levels (normalized)14C CFC-11
CO2
Tracer Air-sea equilibration time
CFC-11 1 month
CO2 1 yr
Bomb C14 10 yr
(ORCA 05, ½° cos ½°) mean res. 33 km
non-eddying
(ORCA 2, 2° cos 2°) mean res. 130 km
TracerTracerss
1950 2000Year
ApproacApproachh
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Global inventory (106 mol) – 1994 (model vs. data)
Increasing resolution reduces CFC-11 uptake & storageIncreasing resolution reduces CFC-11 uptake & storage
non-eddying
eddying Sasai et al (2004)
GLODAP (data)
648 506 510 540
GlobalGlobal AtlanticAtlantic PacificPacific IndianIndian South of South of 20°s20°s
- 22% -33,6% -9,8% -23,5% -28%
- 22% -22,8% -10,8% -36,6% -31%
fluxflux
invinv
Eddy-induced changes (model vs. model)
• Decrease of global uptake by 22% (28% in SO)• Largest flux decrease Atlantic (>33%)• Largest inventory decrease Indian (> 36%)• Eddying model generally agrees with data
non-eddyingeddying
non-eddyingeddyingdata
Inventory
Cumulative flux
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Unlike explictlyGM alone brings little improvement, but not Unlike explictlyGM alone brings little improvement, but not enough…enough…
non-eddying
non-eddying + GM
eddying
eddying + GM
CFC-11 inventory
CFC
-11
Zonal In
tegra
l (M
mol degre
e-1)
non-eddying
non-eddying + GM
eddying + GM
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Global inventory (PgC) - 1994
non-eddying
eddying Sabine et al (2004)
GLODAP
120 98 106 106
GlobalGlobal AtlanticAtlantic PacificPacific IndianIndian South of South of 20°s20°s
- 18% -21,3% -12,5% -23,8% -25%
- 18% -17,9% -14,3% -24,8% -26%
fluxflux
invinv
• Decrease of total uptake by 18% (25% in SO)• Largest air-sea flux decrease Indian (>23%)• Largest inventory decrease Indian (>24%)• Eddying model agrees with data
Global inventory (Pg C) – 1994 (model vs. data)
Eddy-induced changes (model vs. model)
Increased resolution reduces COIncreased resolution reduces CO22 uptake & storage uptake & storage
non-eddyingeddying
non-eddyingeddyingdata
Cumulative flux
Inventory
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How do eddies affect Southern Ocean uptake?How do eddies affect Southern Ocean uptake?
strong upwelling rapid northward transport
Zonal mean CFC-11 saturation in the Atlantic
non-eddying
eddying
Mixed Layer
Thermocline
60°S 40°S 60°S 40°S 60°S 40°S
+ =Eulerian mean circulation
Eddy induced flow
Residual mean circulation
30 Sv -10 Sv 20 Sv
Eddy-induced slow-down of the SO upper meridional circulation
4-year trajectories of set of particles launched at z=250 m, y=60°S, 110°E<x<120°E
weak upwelling
slow northward transport
250 m
250 m
0 m
0 m
100 m
100 m
depth (m)
eddying
non-eddying
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Effect of increasing horizontal resolution Effect of increasing horizontal resolution section I9S – CFC-11 section I9S – CFC-11
Including mesoscale eddies:
reduces excessive penetration of CFC-11 in Southern Ocean
yields a better agreement with data
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- increase of UCDWAAIW: +5 Sv
- decrease of LCDWAAIW (ML): -15 Sv
- reduction of excessive intermediate ocean ventilation (AAIW, - 42%)
non-eddyingeddyingdata
How do eddies affect AAIW ventilation?How do eddies affect AAIW ventilation?
CFC-11 inventory (27-27.4 layer)
Including eddies leads to:LCDWAAIW
UCDWAAIW
SAMW
AAIWUCDWLCDWNADW
SAMW
AAIWUCDWLCDWNADW
Maximum of mixed layer depth
Maximum of mixed layer depth
eddyingIsopycnal meridional streamfunction
non-eddying
30 Sv
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Decrease southern extratropical uptake (improve data-model agreement) CFC-11: -28%; Anthro. CO2: -25%; Bomb C-14: negligible
Increase residence time of tracer-rich waters at the surface Increase surface water saturation of rapid equilibrating tracers (CFC-11,
anthropogenic CO2)
Reduce upwelling (LCDWAAIW) Decrease formation & ventilation of AAIW
modify distribution of AAIW source regions (from circumpolar distribution along ACC to localized in the Pacific Ocean)
decrease vertical penetration of CFC-11 and CO2 (improve data-model agreement)
Need better parameterization or explicit representation of mesoscale eddies to properly simulate southern extratropical uptake & storage of CFC-11 & anthropogenic CO2
Mesoscale eddies:Mesoscale eddies:
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EGU 2006 General Assembly
Future work: Future work: towards eddy-resolving transient tracer simulationstowards eddy-resolving transient tracer simulations
CFC-11 Inventory (1965)
Surface current speed (5-day mean, Jan 1-5)
ORCA2 (2° cos 2°) mean res. 130 km
ORCA05 (½° cos ½°) mean res. 33 km
ORCA025 (¼° cos ¼°) mean res.
17km
From European-led DRAKKAR project on high-resolution ocean
modelling
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Global inventory (1028 atoms 14C) – 1994 (model vs. data)
non-eddying
eddying GLODAP Broeker et al 1995
3,07 2,94 3,13 3,29
GlobalGlobal AtlanticAtlantic PacificPacific IndianIndian South of South of 20°s20°s
- 4,6% -4,7% -4% -6,1% -8%
- 4,6% -5,7% -1,8% -7,3% -7%
fluxflux
invinv
Eddy-induced changes (model vs. model)
• Small decrease of uptake & inventory (<5%)• Good agreement with observation
Global Global 1414C distribution is insensitive to horizontal resolutionC distribution is insensitive to horizontal resolution
non-eddyingeddying
non-eddyingeddyingdata
Cumulative flux
Inventory
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