Utrecht, 16/02/2012 Quantifying the AMOC feedbacks during a 2xCO2 stabilization experiment with land-ice melting Swingedouw Didier

Utrecht, 16/02/2012

Quantifying the AMOC feedbacks during a 2xCO2 stabilization

experiment with land-ice melting

Swingedouw Didier

Utrecht, 16/02/2012

AMOC spread in projections

• Large spread of AMOC response to GHG emissions

• Gregory et al. 2005: heat flux and freshwater flux both play a role

• Need for understanding processes

• Even for a given forcing: large spread

Stouffer et al. 2006

Schneider et al., 2007

Utrecht, 16/02/2012

Opposing effects for the water coming from the Arctic and the tropics

AMOC and salinity

forcing

Swingedouw et al. 2007a

Evaporation

Precipitations

Runoff

Humidity transport

Salinity advection

Utrecht, 16/02/2012

Actuel


AMOC and salinity

forcing


Evaporation

Precipitations

Runoff

Humidity transport

Salinity advection

Utrecht, 16/02/2012

ActuelFutur


AMOC and salinity

forcing


Evaporation

Precipitations

Runoff

Humidity transport

Salinity advection

Utrecht, 16/02/2012

ActuelFuturFutur


AMOC and salinity

forcing


Evaporation

Precipitations

Runoff

Humidity transport

Salinity advection

Utrecht, 16/02/2012

ActuelFuturFuturFutur


AMOC and salinity

forcing


Evaporation

Precipitations

Runoff

Humidity transport

Salinity advection

Utrecht, 16/02/2012

ActuelFuturFuturFuturFutur


AMOC and salinity

forcing


Evaporation

Precipitations

Runoff

Humidity transport

Salinity advectin

Utrecht, 16/02/2012

ActuelFuturFuturFuturFuturFutur


AMOC and salinity

forcing


Evaporation

Precipitations

Runoff

Humidity transport

Salinity advectin

Utrecht, 16/02/2012

Effect –Effect +

Oceanic meridional advection

Temperature density flux

Salinity density flux

AMOCi FCMs

AMOC internal feedbacks

Stocker et al., 2001

Utrecht, 16/02/2012

Effect –Effect +

Oceanic meridional heat transport

Oceanic meridional advection

Meridional atmospheric Temperature gradient

Sea ice amount

Brine rejection

Ekman divergence

Freshwater meridional transport

Sea ice transport and melting

Temperaturedensity flux



THCe TCMOs

Stocker et al., 2001

AMOCi

AMOC internal feedbacks

Utrecht, 16/02/2012

Questions

• How to quantify the mechanisms explaining the response of the AMOC to GHG increase?

• Can an additional freshwater input lead to substantial AMOC weakening in projections?

• What are the roles of feedbacks and forcing for the response of the AMOC?

Utrecht, 16/02/2012

Experimental design

Snow

Land Ocean

Ice

IPSL-CM4 model:• OPA-ORCA2 (0.5°-2°)• LMDz (2.5° x 3.75°)

2xCO2 scenario lasting for 500 years:

• With ice sheet melting• No ice sheet melting

Net heat flux

Temps

(années)

CO2

(ppm)

0 70 500

280

560

CTL

No

With

Time (years))

(Swingedouw et al. 2007b)

Utrecht, 16/02/2012

AMOC and convection sites

Climatology: Boyer Montegut et al., 2005

IPSL-CM4: CTL

• In CTL simulation: AMOC max. of only 11 Sv (obs. around 18 Sv )

• No convection in the Labrador Sea

• Overflow of 5.6 Sv (obs. around 6 Sv)

JFM mixed layer depth

Utrecht, 16/02/2012

• Greenland ice sheet (GrIS) melting amounts to 0.13 Sv after 200 years and is then constant

• Equivalent melting of GrIS by more than 50% after 500 years=very agressive melting scenario

With

CTL

NoAMOC index

Temps

(années)

CO2

(ppm)

0 70 500

280

560

CTL

No

With

Time (years))

Temps

(années)

CTL

No

With

Global temperatureModel responses

Utrecht, 16/02/2012

AMOC and density in the convection sites

Correlation of 0.98 between density in the black box and the AMOC:

t=0

No-CTL

With-CTL

Name of the meeting, 20/06/2011

Influence of haline and thermal response on the AMOC

With melting: Changes in temperature (T) and salinity (S) weakens the density (and AMOC)

TS

T

S

Name of the meeting, 20/06/2011

T

S

T

S

Influence of haline and thermal response on the AMOC

TS

With melting: Changes in temperature (T) and salinity (S) weakens the density (and AMOC)

No melting: Salinity changes explain the recovery

Utrecht, 16/02/2012

Density budget in the convection box

dtdwSSddVSSdvzll

expansionDilutionDiffusionTransportEvolution

)().(.

Transport

Surface

l

Utrecht, 16/02/2012

-2,5

-2

-1,5

-1

-0,5

0

0,5

1

1,5

2

2,5

1 2 3 4 5 6 7

NIS2-CTRL

WIS2-CTRL

Density buget in the convection box after 500 years

AMOC increases

AMOC decreases

Transport Surface Residual

STTSTSResiduResiduSurfaceSurfaceTransportTransport

Budget

No-CTLWith-CTL

Utrecht, 16/02/2012

-2,5

-2

-1,5

-1

-0,5

0

0,5

1

1,5

2

2,5

1 2 3 4 5 6 7

NIS2-CTRL

WIS2-CTRL

Transport Surface Résidu


Bilan

-4

-3

-2

-1

0

1

2

3

1 2 3 4

SoverTransport

SgyreTransport

ToverTransport

TgyreTransport

Sans-CTRLAvec-CTRL

AMOC increases

AMOC decreases

Density buget in the convection box after 500 years

Utrecht, 16/02/2012

Synthesis of important factor explaining density budget in No ice sheet melting

• Over 500 years AMOC reduction mainly caused by:

o Warming in the convection sites (26 %)

o Salinity transport by the overturning (65 %)

• AMOC recovery mainly caused by:

o Transport of salinity anomalies by the gyre (40 %)

o Sea ice melting reduction in the convection sites (28 %)

Utrecht, 16/02/2012

Sea ice melting anomaliesCTL:

• Sea ice transport through Fram Strait

• Brine rejection in winter when sea ice forms

-0,1

-0,05

0

0,05

0,1

0,15

0,2

Local Transport Total

CTRLNIS2

+ =

No melting projections (after 500 years):

• Sea ice transport decreases

• Brine rejection decreases

Sv

Sea ice transport in CTL

CTLNo

Utrecht, 16/02/2012

Salinity anomalies in the Atlantic

SSS anomalies: No melting - CTL

Utrecht, 16/02/2012

Feedback amplification

Linear feedback model (Hansen et al., 1984, for climate sensitivity):

• G0: Static gain

• λi: Feedback factors

0G

1

i

n

+-

Utrecht, 16/02/2012

Feedback quantification methology

now stands for the difference between the projections

We isolate GrIS melting effect:


with

Utrecht, 16/02/2012

-0,4

-0,2

0

0,2

0,4

0,6

0,8

1

1 2

Quantification of feedback factors

5.2)(1

1

TS

G

Dynamical gain:

S T

Climatic system transfer

TemperatureDensity flux

Salinity Density flux

AMOC_in AMOC_out

)( S

)( T

+-+

Utrecht, 16/02/2012

-5

-4

-3

-2

-1

0

1

2

3

4

1 2 Transport Surface Résidu

Salinity Temperature

Transport Surface Résidu

Heat flux feedback strongly damps heat transport feedback

Ocean transport

Temperature density flux


AMOCin AMOCout+

-

Local atmospheric damping

Quantification of feedback factors

Utrecht, 16/02/2012

Quantifying the AMOC feedbacks among different AOGCMs

• For a given freshwater input, large spread among AOGCMs (Stouffer et al. 2006)

• Methodology of feedbacks quantification could be useful (Swingedouw et al. 2007)

• Application to the models from this project framework?

Climatic system transfer

TemperatureDensity flux

Salinity Density flux

AMOC_in AMOC_out

)( S

)( T

+ -+

Stouffer et al. 2006

Utrecht, 16/02/2012

THOR water hosing

• 6 models including one OGCM

• 1965-2005 with 0.1 Sv

Utrecht, 16/02/2012

THOR project: Swingedouw et al., in prep.

An hypothesis to explain AMOC spread

Rypina et al. 2011

Utrecht, 16/02/2012

Outlooks

• Quantifying AMOC feedbacks in the different EMBRACE models

• Evaluating impact of gyre asymmetry on gyre feedbacks factor

Limits/challenges• Computation of density budget in a model• Assumption of AMOC related to density in convection zone holds in other models

Utrecht, 16/02/2012

Predefined sections across the North Atlantic

26N RAPID

OVIDE

A25AR7W

42N

interface between the subtropical and subpolar gyres

overflows : connection between the subpolar gyre and the Nordic Seas

connection with the Arctic ocean

reference salinity : 34.8

Utrecht, 16/02/2012

FCVAR from Julie Deshayes:Diagnostic package of 3D metrics of the circulation

model configurations and simulations

GFDL CM3CNRM CM5IPSL CM5CCSM4+ HADGEM2 ? + HADGEM3 ?pre-industrial control runsmonthly output

+ ocean-only simulationsORCA2-OON2ORCA1-OCEP09ORCA025.L75-G85GLORYS2V1

load grid pointsscale factors

identify sections and areas as sequences of grid points

extract data (t,z,l)along sections and areas

load datau, v, θ, S(t,z,y,x)

predefined sections and areas defined by (lat,lon) of end points+ additional sections

calculate indices (t) for sections, ie components of the northward transport of mass, heat and salt:•net (with and without net mass flux)•overturning in vertical coordinates•overturning in density coordinates•barotropic•baroclinic (net-overturning-barotropic)•0 to1000m deep•1000 to 2000m deep•2000m deep to bottom•related to thermal wind (only from ρ)

calculate indices (t) for areas, regarding heat and freshwater:•volume changes•advective fluxes at ocean boundaries•eddy fluxes at ocean boundaries•diffusion, ice + atmospheric fluxes

Matlab package available

to the community

Utrecht, 16/02/2012

Thank you

[email protected]

Utrecht, 16/02/2012

Convection sites density as a driver of AMOC?

• Strong assumption from the proposed model

• Gregory and Tailleux (2010): buoyancy fluxes over the convection sites as a production of Available potential energy then used for Kinetic energy production

Utrecht, 16/02/2012

Linear feedback factor and hysteresis

• Stommel et al. (1961): non linearity for the response of the AMOC to freshwater input

• This would appears in the feedback factor of the overturning terms for salinity and heat transport (dependent in the mean state)

Utrecht, 16/02/2012

Transport Chaleur Méridien Océanique

Advection Méridienne Océanique

Gradient TempératureMéridien Atmosphérique

Formation Glace

Rejet de Sel Glace

Divergence Ekman, locale

Transport Eau Douce Méridien

Transport, Fonte Glace

Flux DensitéTempérature

Flux Densité Salinité

Flux Densité Salinité

THCe TCMOs

-

Réchauffement climatique

+

+

Action -Action +

Réchauffement climatique

Utrecht, 16/02/2012

Avec fonte : convection disparaît

Sans fonte : renforcement de la convection en mer de GIN, diminution en mer d’Irminger

Réponses des sites de convection

Avec : année 500

CTL

Sans : année 500

Utrecht, 16/02/2012

Représentation de la THC dans le modèle

Fonction de courant latitude-profondeur en Atlantique

Latitude

Profondeur

2 cellules avec NADW et AABW

Maximum pour la NADW d’environ 11 Sv (Indice THC)

Plus faible que les estimations issues d’observations (14-18 Sv)

Sv

Documents

Utrecht, 16/02/2012 Quantifying the AMOC feedbacks during a 2xCO2 stabilization experiment with land-ice melting Swingedouw Didier