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Mélanie JUZA Thierry PENDUFF Bernard BARNIER LEGI, Grenoble, FRANCE

Regional accuracy of global ARGO-based monthly mixed layer property estimates: depth, temperature, salinity. Mélanie JUZA Thierry PENDUFF Bernard BARNIER LEGI, Grenoble, FRANCE. EGU, Vienna, Austria, April 18 th, 2008.

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Mélanie JUZA Thierry PENDUFF Bernard BARNIER LEGI, Grenoble, FRANCE

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  1. Regional accuracy of global ARGO-based monthly mixed layer property estimates: depth, temperature, salinity Mélanie JUZA Thierry PENDUFF Bernard BARNIER LEGI, Grenoble, FRANCE EGU, Vienna, Austria, April 18 th, 2008

  2. Regional accuracy of global ARGO-based monthly mixed layer property estimates: depth, temperature, salinity • 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:

  3. Datasets Observations: ARGO floats from ENACT-ENSEMBLES (Met Office Hadley Center observations datasets)

  4. Datasets Observations: ARGO floats from ENACT-ENSEMBLES (Met Office Hadley Center observations 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)

  5. ¼° Drakkar Model Mixed Layer Depth 2004

  6. Collocation of hydrographic data VALIDATION SAMPLING ERROR COLLOCATED OBSERVED and MODEL T,S(x,y,z,t) profiles Dispersed in time and space Integrated quantities within the mixed layer Statistical analysis ENACT/ENSEMBLES T,S(x,y,z,t) vertical profiles Global. ARGO. 1998-2004 MODEL T,S(x,y,z,t) Global. 1998-2004 • Keep good data only • Quadrilinear collocation (obs. space)

  7. Simulated and observed MLD Mixed layer depths (MLD) (m) August 1998-2004 February 1998-2004 ARGO 1/4° model  Realism of simulated and observed MLD quantities

  8. 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 April 1998-2004 SAMPLING ERROR 17% Median 83% -- full model -- sub-sampled model (like ARGO)

  9. Sampling errors of MLHC in NATL Monthly cycles of MLHC (1998-2004): zone MNW-ATL 16 14 12 10 8 6 4 2 0 MLHC (GJ/m2) -- sub-sampled model -- full model ¼° jan mar may jul sep nov • well observed seasonal cycle • small sampling error. JFM ~ 2 GJ/m2

  10. Sampling errors of MLHC at global scale too warm too cold ARGO sampling error on monthly MLHC (1998-2004) MLHC (J/m2) Error = <sub-sampled model> – <full model> 30° x 30° x 1 month bins (1998-2004)

  11. Sampling errors of MLHC at global scale too warm too cold ARGO sampling error on monthly MLHC (1998-2004) MLHC (J/m2) Error = <sub-sampled model> – <full model> 30° x 30° x 1 month bins (1998-2004)

  12. Sampling errors of MLHC at global scale too warm too cold ARGO sampling error on monthly MLHC (1998-2004) MLHC (J/m2) Error = <sub-sampled model> – <full model> 30° x 30° x 1 month bins (1998-2004) • Sampling errors of MLD and MLT

  13. Regional sampling errors of MLHC, MLD, MLT March 5°C too warm 5°C too cold too warm 100m too shallow too cold 100m too deep  Contribution of MLD / MLT to the ARGO sampling errors of MLHC Sampling error of monthly MLHC/MLD/MLT (1998-2004) MLT MLHC North Atlantic MLD

  14. Regional sampling errors of MLHC, MLD, MLT March 5°C too warm 5°C too cold too warm 100m too shallow too cold 100m too deep  Exact spatial distribution of ARGO floats ¼° model MLD & ARGO floats positions – mar 1998-2004  Contribution of MLD / MLT to the ARGO sampling errors of MLHC Sampling error of monthly MLHC/MLD/MLT (1998-2004) MLT MLHC North Atlantic MLD  Number of data per bin

  15. Regional sampling errors of MLHC, MLD, MLT March 5°C too warm 5°C too cold too warm 100m too shallow too cold 100m too deep ¼° model MLD & ARGO floats positions – mar 1998-2004  Contribution of MLD / MLT to the ARGO sampling errors of MLHC Sampling error of monthly MLHC/MLD/MLT (1998-2004) MLT MLHC North Atlantic MLD - sub-sampled model - full model ¼° MLD

  16. Conclusion-perspectives • 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)

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