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