Data Assimilation and Operational Oceanography: The Mercator experience

Transcription

1 Data Assimilation and Operational Oceanography: The Mercator experience Benoît Tranchant And the Mercator-Ocean Assimilation Team (Marie Drevillon, Elisabeth Remy, Mounir Benkiran, Eric Greiner, Jean-Michel Lellouche, Laurent Parent and Charles Emmanuel Testut)

2 Mercator Ocean: An OPA user but also an OPA developer OPA configurations used in operational (2006): North Atlantic (OPA8.1/rigid lid) MNATL medium (1/3 ) and PAM high (1/15 ) resolution Global (OPA8.2/free surface) ORCA2 and ORCA025 Next important steps: OPA-NEMO: ATL4, ORCA025 and ATL12 in 2007 ORCA12 in 2008 Regional: 1/3 & 1/15 Global: 2 & 1/4

3 2006 Mercator Ocean: A DA user and developer Brief overview of data assimilation schemes: SAM1-v1: Univariate OI (SLA). SAM1-v2: Multivariate OI (SLA, SST and T/S profiles) using 1D vertical modes Operational R&D SAM2-v1: Multivariate SEEK filter (SLA, SST HR and T/S profiles) using 3D modes SAM3-v0: Multivariate 3D-Var (SLA and T/S profiles)

4 Mercator Data Assimilation Systems : SAM 2006 OCEAN MODEL: OPA-NEMO DATA ASSIMILATION SCHEMES SAM1 : OI SAM2 : SEEK filter SAM3 :3D VAR SATELLITE observations IN SITU observations DATA SSALTONEMO userscoriolis meeting 2006 Forcing Fluxes & RTG_SST

5 The Mercator-Ocean forecasting systems satellite altimetry + RTG_SST + in situ data satellite altimetry PSY1v2 Reanalysis Impact studies PSY2Gv1 Oceanic initial conditions for seasonal forecasts satellite altimetry + RTG_SST + in situ data PSY2v2 satellite altimetry PSY3v1

6 North Atlantic prototypes: medium (1/3 ) and high resolution (1/15 ) Based on: 1. OPA 8.1 model, 43 vertical levels Two configurations: North Atlantic 1/3 horizontal resolution North Atlantic + Mediterranean 5 to 7 km hor. resolution 2. PALM_research software (CERFACS) modularity of the coupling model-data assimilation system 3. SAM1v2 data assimilation system: Reduced-Order Optimal Interpolation (ROOI) technique based on SOFA (LEGOS) 1D vertical multivariate Empirical Orthogonal Functions (EOFs) multivariate assimilation of SLA from JASON-1, ENVISAT and GFO, RTG_ SST, REYNAUD SSS climatology and T/S vertical profiles provided by the CORIOLIS centre. In development: ATL4 & ATL12 (OPA-NEMO), 50 vertical levels with the SEEK filter assimilation of SLA, SST HR and T/S profiles using up to 200 multivariate 3D modes for background errors

7 OSE : Impact of PIRATA data PSY1v2 Time serie of temperature profiles at SAMBA mooring (EQ-35 W) In-situ measurements With assimilation of PIRATA data Without assimilation of PIRATA data

8 PSY1v2 Mercator PSY1v2 Reanalysis: MERA Climate : temperature anomalies 350m NAO Cold Subpol Gyre Warm Gulf Stream NAO Warm Subpol Gyre Warm Subtrop Gyre

9 PSY2v2, the Mercator High Resolution Forecasting System for North Atlantic and Mediterranean Sea An example: Eddies in the Gulf of Mexico PSY2v2 Origin, separation and westward progression of an anticyclonic eddy (mid-june to mid-october 2004) 6 weeks from 25 July 2004 to 4 September 2004 Chlorophyll-A (MODIS-CATSAT) SSH (PSY2v2) Very good spatial and temporal agreement between model SSH and satellite Chlorophyll concentration (not assimilated) Warm eddies are characterized by a weak chlorophyll concentration

10 PSY2V2 : T/S profiles impact The Mediterranean Water Outflow PSY2v2 Climatology Salinity at 1000m (2004 temporal mean) PSY2v2 Salinity (11 W,40 N) on 15/08/2004 Model forecast observation

11 North Atlantic prototypes in development: ATL4 with SAM2-v1 Based on: 1. OPA-NEMO model, ice model, free surface and bulk formulae, 50 vertical levels 2. PALM_MP software (MPI-2) enhanced modularity of the coupling model-data assimilation system 3. SAM2v1 data assimilation system: Based on SEEK filter (LEGI) 3D multivariate seasonal anomalies (O 2 ), adaptative variance (P/2), control vecto (Hbar,T, S, U,V) Data assimilation of SLA, RTG_ SST, SST HR and T/S vertical profiles. First analysis increments of salinity and temperature in january 2004

12 GLOBAL PROTOTYPES Low resolution & Eddy permitting resolution 1. Model: ORCA2 OPA 8.2 free surface, 31 vertical z-levels, 2 hor. resolution and ½ in the tropics 2. Palm software 3. Assimilation methods: Operational : Assimilation of SLA data (OI, Cooper and Haines lifting/lowering method) used for seasonal forecasting 1. Model: ORCA025 OPA8.2 free surface, 46 vertical z-levels, ¼ hor. resolution 2. Palm software 3. Assimilation methods: Operational: Assimilation of SLA data (OI, Cooper and Haines lifting/lowering method) operational since october 2005 Data Assimilation schemes in development: Multivariate assimilation of SLA and T and S in situ data with 3D modes (method based on SEEK filter, LEGI) Multivariate assimilation of T/S in situ data and SLA with a 3D-var method (based on ORCAVAR, CERFACS) Model in development: ORCA025-LIM (50 vertical z- levels, 1m-450m) ORCA12-LIM

13 Validation with independent in situ data TAO/TRITON moorings in the Tropical Pacific Ocean PSY3v1 140 W O N Temperature of the global system 110 W 5 S Temperature of the global system Temperature observed by the TAO buoy Temperature observed by the TAO buoy C

14 A basis for global climate monitoring PSY3v1 Global system heat content in 2005 (0-700m), in J/m 2 Climate change indicators Average depth of the 26 C isotherm in the global forecasting system in September 2005 hurricane indicators

15 Seasonal forecasting activity with ORCA2: First results obtained with SAM2 (SEEK) ALL1: assimilation of SLA, in situ T,S profiles and SST data (T/P, JASON, ERS2, ENVISAT, ENSEMBLE, RTG_SST) Reduced order Kalman filter (SEEK formulation), with 200 multivariate 3D modes ALL1 vs Control run ALL1 Control run Std dev. Improvement (0< means better) Equipe R&D assimilation

16 SAM3 Based on ORCAVAR v1.x Intercomparion experiment with SAM2 = - 3DVar : OPAVAR version with the «default options» (background error covariance matrix, ), - ENACT like experiments: corrected ERA40 fluxes, a=-200w/m2/k, - ORCA2: free surface constant volume: daily correction of E-P. - along track T/P sla assimilated (filtered for ORCA2), MDT Rio V5.1 - observation error covariance matrix: 3D for T and S, 2D for altimetry computed using the Fu. et al. method (1993): <rr>=<yy>-<ym> Representativity NEMO error users : meeting SLA, zonal 2006T mean

17 SSH and heat content evolution from 0 to 300 m ( ) Mean HC(2001) Mean HC(1993) in C Mean SSH (2001) Mean SSH (1993) in m Data: Merged satellite Products Assim. in situ + T/P (IAO) Control Data 65 N-65 S Temperature anomalies (0 300m/60 N-60 S) SLA global 60 N-60 S

18 Summary 2006 OPAx and SAMx OPA8.1 OPA8.2 SAM1v1 SAM2v1 OPA9 SAM1v2 SAM3 Analysis and 2 week forecasts every week:psy1v2,psy2v2,psy2gv1 and PSY3V1 Reanalysis: MERA11 OSE/OSSE:Pirata impact, SSS assimilation from SMOS and Aquarius (Newsletter #21:April 2006) Seasonal forecasting Reanalysis with ORCA025 planned in 2007 with SAM2.

19 Perspectives 2006 Upgrade of data assimilation schemes: SAM2-vx A better way to assimilate largest scales (H) Smoother/IAU Adaptative covariances (time dependent) Data assimilation of surface currents (drifters/radar) and ice concentration SST HR Estimation of representativity errors (obs. errors) Numerical Optimization for huge configuration (ORCA Gb): PALM_MP using. SAM3-vx improvement of salinity assimilation Improvement of B matrix Coupling SAM2 with OPA-NEMO configurations: ATL4 and ORCA025-LIM : end of 2006/ beginning of 2007 ATL12 in 2007 ORCA12 in 2008