Improving the initialisation of our operational shelf-seas models

Transcription

1 Improving the initialisation of our operational shelf-seas models Robert King James While, Matt Martin, Dan Lean, Jennie Waters, Enda O Dea, Jenny Graham NPOP May 2018

2 Contents 1. Recent history developments to AMM7 2. Upcoming changes AMM15 status 3. Future developments plans for data assimilation over next 3-5 years

3 Introduction AMM7 Forecasting Ocean Assimilation Model configuration covering the North-West European Shelf Seas (FOAM-Shelf). Ocean model is NEMOv3.6 in the AMM7 configuration 7km resolution, 51 vertical sigma-levels Tidal, wind- and pressure-forced model forced by Met Office NWP fluxes and LBCs from Met Office 1/12⁰ North Atlantic Model and Baltic MFC. Data assimilation scheme is NEMOVAR. 3DVar FGAT with 24-hour window Multi-scale background errors, multivariate balance

4 Recent History: AMM7v8 (oper < Apr 2017) AMM7v8 7km resolution, used NEMOVAR to assimilate SST observations ONLY. Significant biases, some controlled but significant subsurface biases remained. Plots show 30-year mean differences between AMM7 and WOA CO5 free run - WOA Temperature CO5 with assim - WOA

5 Recent History: AMM7v8 (oper < Apr 2017) AMM7v8 7km resolution, used NEMOVAR to assimilate SST observations ONLY. Significant biases, some controlled but significant subsurface biases remained. Plots show 30-year mean differences between AMM7 and WOA CO5 free run - WOA Salinity CO5 with assim - WOA

6 Recent History: AMM7v9 (oper since Apr 2017) Temperature profiles Salinity profiles Example coverage of T/S profile observations for 1-month (Sept 2017). Example coverage of SST observations for 1-day. Example coverage of satellite altimeter observations for 1-day from Sentinal-3, Jason-3, Cryosat and AltiKa.

7 Recent History: AMM7v9 (oper since Apr 2017) New system with assimilation of SST, SLA, and T/S profiles Large reduction (>25%) in T/S RMS errors compared to v8 system. Assimilation of SLA also introduces eddy-scale features to our analyses which compares well with altimeter-derived surface current estimates. Temperature Salinity Left: Mean surface currents for January 2015 from AMM7v8 and v9 and from observation-derived current products. Right: Depth profile of temperature (left) and salinity (right) innovation statistics from AMM7 v8 (grey) and v9 (black) averaged over full domain and 2- year period. OLD NEW --- mean error RMSE OLD NEW King et al., Ocean Modelling, 2018, submitted

8 Upcoming changes: AMM15 Currently upgrading the ocean model component of FOAM-Shelf. Higher resolution, slightly smaller domain. New, higher resolution bathymetry and coastline. No change in vertical resolution. AMM7 Can now begin to resolve mesoscale eddies, internal tides. Leads to improved vertical mixing and reduced surface T/S biases. AMM15

9 Upcoming changes: AMM15 Currently upgrading the ocean model component of FOAM-Shelf. Higher resolution, slightly smaller domain. New, higher resolution bathymetry and coastline. No change in vertical resolution. Can now begin to resolve mesoscale eddies, internal tides. Leads to improved vertical mixing and reduced surface T/S biases.

10 Upcoming changes: AMM15 (no assimilation) Seasonal SST anomalies: Comparison with OSTIA ( ). Reduced overall bias in AMM15 compared to AMM7, but improvement is greater off-shelf. From Graham et al. 2017

11 Upcoming changes: AMM15 with assimilation AMM15 assimilation follows same approach as for AMM7 SST T profiles Assimilation of satellite and in situ SST data, satellite altimeter SLA data (in the deep part of the domain), and in situ temperature/salinity profiles has been implemented in AMM15 SLA S profiles Obs coverage for Feb 2017

12 Upcoming changes: AMM15 with assimilation First implementation of DA in AMM15 has similar short-term accuracy to AMM7. SST ( C) AMM7 Retains high resolution model information. Longer experiments of this system are currently being run and assessed. System is expected to be made operational later in AMM7 AMM15 AMM15 1 st Feb 2016

13 AMM15: impact of assimilation T profiles S profiles SLA mean bias NoAssim Assim SST T profiles ASSIM NO ASSIM ASSIM NO ASSIM

14 AMM15: impact of resolution T profiles S profiles SLA mean bias AMM7 AMM15 SST AMM15+DA AMM7+DA AMM15+DA AMM7+DA

15 Future Developments 2018: Test changes to vertical mixing and light attenuation schemes. Aim to decrease on-shelf biases. 2018/19: Implement existing DA system within the coupled oceanwave model. Test new high resolution altimeter observations better match scales of AMM15. Estimate new error co-variances for AMM : Upgrading DA to work with NEMO4.0 and wetting-anddrying. Prepare for SWOT swath altimeter providing SLA obs with similar coverage to SST. Investigate assimilation of altimeter SLA data in shallower waters.

16 Summary Operational AMM7v9 has significantly reduced biases through assimilation of new observation types Higher resolution AMM15 allows for fine scale detail of flow speed, variability and begin to resolve mesoscale eddies and internal tides. Existing assimilation capability has been implemented in AMM15 and will be operational later in Various developments planned over coming few years: Implement DA in coupled ocean-waves model and tune the error co-variances. Implement DA in NEMO4.0 with wetting-and-drying. Improve the assimilation of altimeter data and prepare for SWOT.