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
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)
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.
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
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
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
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
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
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
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
- 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
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:
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
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