1. © Crown copyright Met Office UK report for GOVST Matt Martin GOVST-V, Beijing, October 2014.

2. © Crown copyright Met Office Contents Developments for new version of FOAM (v13). On-going developments Summary

3. © Crown copyright Met Office Development of new global FOAM version Overview FOAM V12 is reported in Blockley et al., 2013: NEMO model (vn 3.2) NEMOVAR data assimilation (3DVar-FGAT) ¼° global, 1/12° regional (N. Atlantic, Indian Ocean, Med). Main short-comings which were identified (partly through GOV class 4 inter- comparisons): Model mixing biases. Sea-ice issues (particularly sea-ice thickness). Inability of DA to control the larger-scale biases in data-sparse areas. FOAM V13 (at NEMO vn3.4) aims to address these issues through: Changes to the TKE mixing scheme (mainly parameter tuning). Sea-ice model (CICE) parameter tuning (increasing the ice albedo and the conductivity of the snow and ice). Implementing multiple length-scales in the NEMOVAR data assimilation scheme. Also increased the number of iterations in the minimisation of the DA.

4. © Crown copyright Met Office Model changes (v12 vs v13) Temperature biases warming at 100m cooling at 500m FOAM v12 (like GO1) New model (GO5) Old model (GO1) model drifts model bias and RMS From D. Storkey

5. © Crown copyright Met Office freshening in top 400m salinification at depth FOAM v12 model drifts model bias and RMS From D. Storkey Old model (GO1) New model (GO5) Model changes (v12 vs v13) Salinity biases

6. Development of new global FOAM version Data assimilation developments The model biases described before imply a large-scale component to the errors. In FOAM V12, the NEMOVAR system only had a small-scale covariance model, with the errors being corrected over length-scales of the Rossby radius. In FOAM V13, we implemented code in NEMOVAR to include multiple length-scales in the correlation model. Two length-scales are now modelled, the smaller one is still based on the Rossby radius, the larger one is 400km everywhere. The ratio of the variances associated with each scale determines the effective length-scale. With a larger-scale component, we also increased the number of iterations in the minimisation of the 3DVar cost function. Old error correlation length-scale (km) Work by I. Mirouze Large length-scale (400km) Small length-scale Effective length-scale

7. © Crown copyright Met Office Development of new global FOAM version Results: temperature profile errors Significant reduction in mean temperature errors between 50-200m depth. Mainly due to model mixing improvements. Also improved by the 2 length-scales in the DA. RMS errors also slightly reduced. V12 system global errors V13 system global errors From E. Blockley

8. © Crown copyright Met Office Development of new global FOAM version Results: salinity profile errors V12 system global errors V13 system global errors Significant reduction in mean salinity errors over the top 300m. Mainly due to the 2 length-scales in the DA. Improvements mainly in the Southern Ocean. RMS errors also slightly reduced. From E. Blockley

9. © Crown copyright Met Office Development of new global FOAM version Relative impact of model & DA changes Model changes improve the temperature biases, particularly in areas such as the South Pacific DA changes further reduce biases and RMS errors. A small increase in deeper errors (~1000m) -> further tuning of error covariances required. Model changes improve the salinity biases and RMS errors, particularly in areas such as the Southern Ocean. DA changes further reduce biases and RMS errors. BLACK => Old model, old DA BLUE => New model, old DA RED => New model, new DA

10. © Crown copyright Met Office Development of new global FOAM version Results: sea-ice volume and extent Ice volume increased from model tuning (albedo and conductivity). Much better agreement with PIOMAS volume. Ice extent now has smaller drift in the forecasts than the v12 system. From A. McLaren and E. Blockley

11. © Crown copyright Met Office Development of new global FOAM version Status and plans Results of V13 vs V12 trials: Significant improvements in sub-surface T&S biases SSH slightly degraded in the Southern Ocean regions -> could be balance issues in the DA given the large improvements in salinity there. No/little impact on the surface current forecast accuracy. Improvements in sea-ice extent and volume. Small reduction in SST RMS error from 0.49 to 0.47K. Operational implementation of the V13 system expected early 2015. Long reanalysis (1989 – 2013) with the V13 system also being produced (for seasonal forecast calibration purposes).

12. © Crown copyright Met Office On-going developments Development of 1/12° global configuration 1/4°1/12° Surface current speed (5 day mean) Boundary currents and extensions change dramatically between ¼° and 1/12° with potentially important implications for biases and air-sea fluxes/coupling. The ORCA12 NEMO model configuration has been run at the Met Office. Based on a configuration developed within the DRAKKAR consortium. NEMOVAR now being implemented in ORCA12. P. Hyder and J. Waters

13. © Crown copyright Met Office Coupled forecasts currently being produced operationally: ¼° ocean/sea-ice, ~60km atmosphere/land. Initialised using FOAM ocean/sea-ice analysis and Met Office NWP atmosphere/land analysis. Ocean forecasts from the coupled system provided through MyOcean. Developments: Weakly coupled data assimilation system. Higher resolution model (1/12° ocean/sea-ice, 17km atmosphere/land). Improving the coupling through implicit solver for SST to improve diurnal cycle. Weakly coupled DA system planned to be implemented as a demonstration operational system in 2015. On-going developments Coupled prediction

14. © Crown copyright Met Office New FOAM system (v13) planned to be implemented in early 2015. Coupled predictions (¼° ocean/ice ~60km atmosphere/land) using FOAM as initial ocean conditions and NWP analyses as initial atmospheric conditions now operational (forecasts for MyOcean). New weakly coupled DA system (at the same resolution) being developed to improve initialisation of these coupled forecasts. Now developing higher resolution coupled system (1/12° ocean/ice ~17km atmosphere/land) which could provide NWP and ocean forecasts in a few years. Move to new supercomputer, starting in 2015. Expected to provide an order of magnitude increase in computing power overall in about 2 years from now (phased increase). Summary

15. © Crown copyright Met Office Thank you

16. © Crown copyright Met Office Additional slides

17. © Crown copyright Met Office

18. Dec 2010Dec 2012 Dec 2010Dec 2012 Development of new global FOAM version SST statistics: Global reduction in RMS error from 0.49 to 0.47 Sea-ice concentration statistics: Global increase in RMS error from 2.9% to 3%

19. © Crown copyright Met Office Development of new global FOAM version SSH statistics: Global increase in RMS error from 7.1cm to 7.5cm Mainly due to degradation in the Southern Ocean Dec 2010Dec 2012 Dec 2010Dec 2012

20. © Crown copyright Met Office Development of new global FOAM version Surface currents compared to drifters Little impact on the surface current forecasts or analyses.

21. © Crown copyright Met Office Monthly mean W 06/2011 – equatorial sections Free run DA with no pcbias DA + inst pcbias + orig pcbias

22. © Crown copyright Met Office Monthly W standard deviation 06/2011 – equatorial sections Free run DA with no pcbias DA + inst pcbias + orig pcbias

23. © Crown copyright Met Office Impact of horizontal resolution Current speed (5 day mean) Demonstrates the impact of horizontal resolution on surface ocean currents. For example, boundary currents and extensions change dramatically between ¼ and 1/12 th with potentially important implications for biases and air-sea fluxes/coupling. 1 deg ¼ deg 1/12 th deg From Pat Hyder

24. © Crown copyright Met Office Global 1/12° NEMOVAR in FOAM Status The ORCA12 NEMO model configuration has been run at the Met Office. Based on a configuration developed within the DRAKKAR consortium. Basic technical work to implement NEMOVAR within this configuration has been undertaken. For an example day: Observation operator has been run. Basic version of NEMOVAR has been run. Increments have been added into the model. Some work was required to make the observation operator and the NEMOVAR step more efficient: Reading observations in batches and assign to correct processor. Removal of some global arrays and implementation of alternative techniques for locating observations on the model grid.

25. © Crown copyright Met Office In the tropics, data assimilation causes spurious vertical motions which disrupt the velocities (horizontal and vertical). In FOAM a pressure correction is applied to maintain balance between the wind stress and the ocean density field in tropical regions to alleviate this. The pressure correction is a slowly evolving bias field which is updated at each analysis step using the temperature and salinity increments. However, even with the pressure correction we still get a strong equatorial response with spurious vertical velocities and equatorial waves. We are investigating the application of an “instantaneous pressure correction” to attempt to reduce the impact of the DA on the velocities in the tropics. On-going developments Data assimilation in the tropics