1. Ocean and sea-ice data assimilation and forecasting in the TOPAZ system L. Bertino, K.A. Lisæter, I. Kegouche, S. Sandven NERSC, Bergen, Norway Arctic ROOS meeting, 18 th Dec. 2007

3. Motivation  Objective:  Provide short-term (10 days) forecasts of physical and biogeochemical ocean parameters to the public at large and intermediate users.  Strategy  Focus on advanced data assimilation techniques  Gradual increase of resolution (as affordable…)  Nesting on regions of higher interest

4. Method  The ice-ocean system has two sources of information  A nonlinear ice-ocean model  A regular flow of observations  Uncertainties arise primarily from  The initial state  Surface boundary conditions  Measurements errors  Monte Carlo methods can handle non-linear dynamics.  Provide the best estimate  Provide the residual uncertainty  Each source of uncertainty must be simulated realistically.

5. Sequential data assimilation Recursive Monte Carlo method ForecastAnalysis Observations 1.Initial uncertainty 2.Model uncertainty 3.Measurement uncertainty 1 2 3 Member1 Member2 …… Member99 Member100

6. The TOPAZ model system  TOPAZ: Atlantic and Arctic  HYCOM  EVP ice model coupled  11- 16 km resolution  22 hybrid layers  EnKF  100 members  Sea Level Anomalies (CLS)  Sea Surface Temperatures  Sea Ice Concentrations (SSM/I)  Sea ice drift (CERSAT)  Runs weekly since Jan 2003  ECMWF atmos. forcing

7. Model upgrade Doubling the horizontal resolution TOPAZ2: 18 to 36 km TOPAZ3: 11 to 16 km TOPAZ2 TOPAZ3

8. System Validation Consistency? Accuracy? Performance?

9. Consistency: Against Climatology TOPAZ2TOPAZ3 Temperature anomalies at 30 m depths

10. Accuracy: against ice concentrations TOPAZ2TOPAZ3 Model minus obs.

11. Accuracy Against in-situ profiles from NPEO Aerial CTD casts TemperatureSalinity

12. Assimilation on 4 th and 11 th April Up to +10 days forecast

13. Forecast skills: Barents Sea - ice concentrations Average Winter 2007Average Summer 2007

14. Ice drift validation  In-situ  Ice drifting buoys (Statoil/CMR)  Manned expeditions  Remote sensing  ASAR (NERSC) WP2  QuickSCAT (Ifremer)  Modelling  TOPAZ V1, class 1  A good agreement [ J. Wåhlin]

15. Historical minimum Arctic sea-ice area, summer 2007 Observed sea-ice from SSM/I, NORSEX algorithm

16. Forecasting the ice minimum in TOPAZ Overlay of successive forecasts TOPAZ catches the freeze-up

17. Products Standards Delivery Timeliness

18. What products?  MERSEA products  Class 1:  3D daily fields  ocean and sea-ice  Anomalies to climatolgy  Class 2:  Predefined sections  Predefined moorings  Class 3:  Volume fluxes through sections  Salt and heat transports  Class 4:  Differences with observations,  Forecast skills  Other products (targeted)  Ensemble uncertainties,  Predicted drift  Icebergs

19. Class 2 metrics  Sections stored daily Moorings stored daily

20. Uncertainty estimates example sea-ice thickness Ensemble average 13 th March 2007 Ensemble standard dev. 13 th March 2007

21. Forecasting the drift of Tara  TOPAZ successive forecasts in red  Actual positions of Tara from DAMOCLES in black  Updated on Google Earth [ K. A. Lisæter]

22. 8m draft Iceberg simulations  An iceberg is sensitive to  Winds  Waves  Currents  Ice drift  Ice thickness  Iceberg shape  Tides  Melting  … 13m draft 18m draft [ I, Keghouche, NERSC ]

23. Availability  Forecast updated every Thursday  10 days forecast horizon  Available freely via  Webpage http://topaz.nersc.no (static pictures)http://topaz.nersc.no  OPeNDAP http://topaz.nersc.no/thredds (data)http://topaz.nersc.no/thredds  No password required  But feedback is welcome  Available to date  TOPAZ2: October 2005 to October 2007  TOPAZ3: July 2007 to present

24. Plans  Ongoing projects (MERSEA, BOSS4GMES)  Assimilation of additional data (Argo)  Inclusion of ecosystem model  NORWECOM from IMR, Bergen.  RT exploitation of TOPAZ at met.no  Developments of TOPAZ at NERSC  Exploitation at met.no (ongoing)  Planned project MyOcean (2008-2011)  30-years reanalysis