Operational forecasting at the Met Office using NEMO

1. Operational forecasting at the Met Office using NEMO Dave Storkey

2. Contents • Current operational systems • Rationale for changing to NEMO • Progress with transition: • deep ocean • shelf

3. Operational deep ocean forecasting (FOAM) • Daily analyses and 5-day forecasts • Based on ocean component of MetO Unified Model. • Global coverage (1 deg resolution) with nested models down to ~10km resolution • OI assimilation scheme • Fluxes from NWP model.

4. Operational deep ocean forecasting (FOAM) 1º Global 36km (1/3º) North Atlantic and Arctic 12km (1/9º) North Atlantic 12km (1/9º) Mediterranean 27km (1/4º) Antarctic 12km (1/9º) Arabian Sea

5. Operational shelf seas forecasting • Daily nowcasts and 3-day forecasts. • Based on POLCOMS. • Nested 12km – 1nm models in NW European shelf • Tidal harmonic forcing at lateral boundaries • Fluxes from NWP model. • Runoff from 47 sources (rivers and Baltic) • No assimilation.

6. Operational shelf seas forecasting 12km Atlantic Margin Model FOAM 12km (1/9º) North Atlantic 1nm Irish Sea Model 6km MRCS Model

7. Rationale for transitioning to NEMO • UM ocean model reaching the end of its life. • Facilitate collaboration with other European groups. • Enable FOAM and Shelf groups in the the Met Office to work more closely together and share developments (eg. assimilation code). • Modular, F90 code easier to maintain.

8. Transition of FOAM system • FOAM-NEMO configuration: • filtered free surface • direct flux forcing • LIM2 sea-ice. Aim to use CICE soon. • TVD advection • TKE vertical mixing • Assimilation using FOAM OI scheme as stand-alone code with observation operator (Greg Smith, ESSC) and increments code (Matt Martin) within NEMO. Will use NEMOVAR system in the longer term.

9. Transition of FOAM system • Hoping to transition all FOAM operational suites to NEMO by April 2009. • Initial FOAM-NEMO system will be based on ORCA025 and N Atlantic 1/12° configurations. High near-surface vertical resolution. • ORCA025 configuration being tested in trial operational suite. • Initial results reasonable, but testing very slow due to resource usage (min 2 nodes of NEC SX8). • Performance/scaling issues.

10. FOAM-ORCA025: SST after 3 months spin up Temperature range: 0 - 32 °C

11. FOAM-ORCA025 : temperature verification stats

12. Transition of Shelf Seas system • Shelf-NEMO configuration: • Timesplit surface pressure gradient calculation. • Sigma coordinate in vertical with new pressure gradient schemes (to be tested). • Nonlinear free surface (variable volume). “Bug fix” for strongly nonlinear flows. • Tidal harmonic forcing as part of BDY open boundary module. • GOTM. • Online harmonic analyser.

13. Transition of Shelf Seas system • Aim to have initial trial operational implementation in summer 2008. • Main development and validation now being done by Jason Holt at POL. • Tides-only tests in 12km model show good comparison with equivalent POLCOMS simulations. • Full baroclinic simulations being set up with a view to validating for period of North Sea Project.

14. Shelf Seas: cotidal charts for barotropic integration with M2 forcing POLCOMS NEMO

15. Summary • Transition to NEMO under way for FOAM and Shelf Seas systems. • Still at the stage of setting up operational configurations – not much validation yet. • Within next FY, hope to have entire FOAM system transitioned and a trial operational Shelf system.