Regional accuracy of global ARGO-based Regional accuracy of global ARGO-based monthly mixed layer property estimates: monthly mixed layer property estimates:

depth, temperature, salinitydepth, temperature, salinity

Mélanie JUZAMélanie JUZAThierry PENDUFFThierry PENDUFFBernard BARNIER Bernard BARNIER

LEGI, Grenoble, FRANCELEGI, Grenoble, FRANCE

EGU, Vienna, Austria, April 18 th, 2008

Interest of ARGO array for climate

- Monitoring and research

Determination of the observable part of the ocean dynamics

- Accuracy of the ARGO array (OSSE approach)

Heat content within the mixed layer:

Regional accuracy of global ARGO-based Regional accuracy of global ARGO-based monthly mixed layer property estimates: monthly mixed layer property estimates:

depth, temperature, salinitydepth, temperature, salinity

0

0

MLDz

TdzCpMLHC

Datasets

Observations: ARGO floats

from ENACT-ENSEMBLES (Met Office Hadley Center observations datasets)

Datasets

1958-2004 numerical simulation : DRAKKAR ¼°

DRAKKAR Group 2007, Barnier et al 2006, Brodeau et al 2007, Penduff et al 2008

- NEMO code (ocean model OPA9 + sea-ice LIM2 + CFC11 + 14C)

- Global setup.

- Resolution: 1/4° . 46 vertical levels

- Interannual forcings 1958-2004: BULK formulae (COARE)

- Turbulent fluxes: atmospheric variables (from ERA40 reanalysis)

- Radiative fluxes: ISCCP satellite observations

- Precipitations (Xie and Arkin)

- Runoffs (Dai and Trenberth)

- Outputs: U , V, T, S, SSH … (5 day means)

Observations: ARGO floats

from ENACT-ENSEMBLES (Met Office Hadley Center observations datasets)

¼° Drakkar Model

Mixed Layer Depth

2004

Collocation of hydrographic data

ENACT/ENSEMBLEST,S(x,y,z,t) vertical profilesGlobal. ARGO. 1998-2004

MODELT,S(x,y,z,t)Global. 1998-2004

• Keep good data only• Quadrilinear collocation (obs. space)

COLLOCATEDOBSERVED and MODEL

T,S(x,y,z,t) profiles Dispersed in time and space

VALIDATION SAMPLING ERROR

Integrated quantities within the mixed layer

Statistical analysis

Simulated and observed MLD

ARGO

August 1998-2004 February 1998-2004

Mixed layer depths (MLD) (m)

1/4°

model

Realism of simulated and observed MLD quantities

Method for the analysis of mixed layer quantities

Distribution of Mixed Layer Depth / Temperature / Salinity / Heat and Salt Contents

Medians and percentiles 17% and 83%

Example: MLHC in North Atlantic

Median

17%

83%

0

0

MLDz

TdzCpMLHC

-- full model -- sub-sampled model (like ARGO)

SAMPLING ERROR

April

1998-2004

Sampling errors of MLHC in NATL

-- sub-sampled model

-- full model ¼°

Monthly cycles of MLHC (1998-2004): zone MNW-ATL

well observed seasonal cycle

small sampling error. JFM ~ 2 GJ/m2

jan mar may jul sep nov

16

14

12

10

8

6

4

2

0

ML

HC

(G

J/m

2 )

Sampling errors of MLHC at global scale

ARGO sampling error on monthly MLHC (1998-2004)

30° x 30° x 1 month bins (1998-2004)Error = <sub-sampled model> – <full model>

MLHC (J/m2)

too warm

too cold

Sampling errors of MLHC at global scale

ARGO sampling error on monthly MLHC (1998-2004)

30° x 30° x 1 month bins (1998-2004)Error = <sub-sampled model> – <full model>

MLHC (J/m2)

too warm

too cold

Sampling errors of MLHC at global scale

ARGO sampling error on monthly MLHC (1998-2004)

30° x 30° x 1 month bins (1998-2004)Error = <sub-sampled model> – <full model>

MLHC (J/m2)

too warm

too cold

Sampling errors of MLD and MLT

Regional sampling errors of MLHC, MLD, MLT

Sampling error of monthly MLHC/MLD/MLT (1998-2004)

Contribution of MLD / MLT to the ARGO sampling errors of MLHC

MLHC

North Atlantic

MLD

too warm

too cold

MLT

5°C too warm

5°C too cold

100m too shallow

100m too deep

0

0

MLDz

TdzCpMLHC

March

Regional sampling errors of MLHC, MLD, MLT

Sampling error of monthly MLHC/MLD/MLT (1998-2004)

Contribution of MLD / MLT to the ARGO sampling errors of MLHC

MLHC

North Atlantic

MLD

too warm

too cold

MLT

5°C too warm

5°C too cold

100m too shallow

100m too deep

Number of data per bin

March

Exact spatial distribution of ARGO floats

¼° model MLD & ARGO floats positions – mar 1998-2004

Regional sampling errors of MLHC, MLD, MLT

Sampling error of monthly MLHC/MLD/MLT (1998-2004)

Contribution of MLD / MLT to the ARGO sampling errors of MLHC

MLHC

North Atlantic

MLD

too warm

too cold

MLT

5°C too warm

5°C too cold

100m too shallow

100m too deep

¼° model MLD & ARGO floats positions – mar 1998-2004

- sub-sampled model

- full model ¼°

MLD

March

Preliminary estimates at global scale:

- ARGO sampling error in mixed layer

and Salinity and Salt Content …

- Dependence on spatial distribution of ARGO floats

Interest of numerical simulations to assess the accuracy of observation systems

Extend this assessment : to recent years (maximum ARGO coverage)

: toward the last 50 years (interannual cycles)

Conclusion-perspectives

Typical Max

Depth +/- 10 m +/- 100 m

Temperature +/- 1 °C +/- 5 °C

Heat content +/- 1 GJ/m2 +/- 5 GJ/m2