1. U.S. Navy Global Ocean Prediction Update Key Performers: A.J. Wallcraft, H.E. Hurlburt, E.J. Metzger, J.G. Richman, J.F. Shriver, P.G. Thoppil, O.M. Smedstad, L. Zamudio 2011 GODAE OceanView Technical Workshop on Observing System Evaluation and Inter-comparison 13-17 June 2011 Santa Cruz, CA

3. Modeling tides in the global model In the global model, the body forces due to the tidal potential, self attraction and loading have been added Tidal Forcing with 8 constituents: – –Semidiurnal M 2, S 2, N 2 and K 2 – –Diurnal O 1, P 1, Q 1 and K 1 Topographic wave drag is applied to the tidal motions – –The form of the drag is generalized from the linear topographic wave drag, but tuned to minimize the difference with the 102 pelagic tide gauges using a barotropic version of the model

4. Comparison of M 2 tide from Data- Assimlative Shallow Water Model (TPXO7.2) and HYCOM Simulation TPXO7.2 M 2 Tidal Model HYCOM M 2 Tide Difference with 102 pelagic tide gauges 7.8 cm rms Difference with TPXO7.2 model 5.4 cm rms

5. cm M 2 internal tide amplitude: along-track altimetry data vs 1/12  Global HYCOM Altimetry-based analysis HYCOM Analysis of along-track altimetry data based upon extracting the aliased tidal signal from the repeat-cycle data as described by Ray and Mitchum (1996, 1997) The internal tide is recovered by a spatial filter to separate the barotropic and baroclinic tides Atlimeter analysis provided by Richard Ray HYCOM SSH analyzed for tides, sampled along track and filtered similar to altimeter

6. Altimetry-based analysis cm HYCOM M 2 internal tide amplitude: along-track altimetry data vs 1/12  Global HYCOM

7. Large Scale Prediction GOFS V3.5 1/25° non-assim. global HYCOM 1/12° non-assim. global HYCOM Mean SSH 2004-2009 Forced with 0.5° NOGAPS winds and heat fluxes

8. Large Scale Prediction GOFS V3.5 1/25° non-assim. global HYCOM 1/12° non-assim. global HYCOM SSH Variability (cm) 2004-2009 Satellite observations from CLS

9. HindcastNCODASyntheticsCICE 1MVOIMODASNo 23DVARMODASNo 33DVARISOPNo 43DVARISOPYes 1/12° NCODA(3DVAR) / ISOP / CICE Hindcast Matrix Hindcasts 1-3 will cover approximately a three month period and incrementally build upon each other. It is anticipated that hindcast four will be the final configuration of GOFS V3.1 and so this will be integrated an entire year. Plans for 1/12° Global Forecast System (GOFS 3.1)

10. FY12 Plans for 1/25° System (GOFS 3.5)

11. Near real-time 1/12° global HYCOM/NCODA prediction system output (Nov 2003-present) 1/12° global non-assimilative HYCOM output (2003-2006) 1/12° North Atlantic data assimilative HYCOM output (2003-2008) 1/12° Pacific non-assimilative HYCOM output (1979-2003 – monthly means) Variables remapped to 33 standard levels: 3D – T, S, U, V, ρ; 2D – SSH, SST, SSS, MLD, … HYCOM Data Serving http://www.hycom.org/dataserving

12. 1/12º Global HYCOM Questions?

13. ISOP corrects climatological or model backgrounds based on climatologically observed modes of variability Background from climatology or model forecast + uncertainty in situ observations + uncertainty Remote sensing (SST, SSH) + uncertainty Mixed-layer depth estimate + uncertainty Synthetic profile of T,S or corrections to background ISOP EOFs of T, S Model mixed layer, deep layer, transitions minimize variance among background, observations

14. Eddy Kinetic Energy at the Surface Eddy Kinetic Energy (cm 2 /s 2 )

15. Eddy Kinetic Energy at the Surface in the Gulf Stream The 1/25 model has the highest EKE with a larger southern recirculation gyre Data assimilation brings the EKE close to the observations from the drifters

16. Summary of Surface EKE 74.2, (1/12  ) DA 04.2, (1/25  ) FR 18.2, (1/12  ) FR 18.5, (1/12  ) FR-T 2008-092005-072005-09 Surface Observed (Drifter) Mean EKE = 418.2; KEMM = 135.4 Mean EKE395.4439.1348.3346.3 KEMM145.3179.9155.2156.0 EKE Correlation 0.7690.8090.8040.802 Increasing the resolution or assimilating data increases the EKE to levels comparable to the drifter observations Increasing the resolution increases the KEM while assimilating data decreases the KEM Part of the doubled resolution EKE increase may be associated with surface quasigeostrophic motions Interannual variability about 15 cm 2 /s 2 in EKE and 20 cm 2 /s 2 in KEM

18. Why does the 1/25° Model Perform so much better? Much emphasis for the global models has been focused on resolving the eddy scales (Rossby radius of deformation) The dynamics are governed by the energy and enstrophy cascades and interactions. – –In the surface enstropy cascades to small scales and energy towards the Rossby radius, where it is transferred in the vertical (barotropization) – –The barotropic eddy kinetic energy can be transferred to the mean (a mechanism for the downstream increase in the Gulf Stream) – –The enstropy cascades are a critical part of this cycle, which are resolved better in the higher resolution model – –Increasing the eddy kinetic energy in the surface by data assimilation improves the model but does adequately resolve the enstropy cascades

19. 1/12° 1/25° – 1/12° 1/12° Tides – 1/12°1/12° DA – 1/12° Differences in Surface Eddy Kinetic Energy (cm 2 /s 2 ) Surface Eddy Kinetic Energy

20. Deep Eddy Kinetic Energy in the Gulf Stream Region

21. What happens in the simulations? We find that the resolution of the present generation of ocean general circulation models of ~1/10° is inadequate to establish a vigorous abyssal circulation and the surface eddy kinetic energy (EKE) is only about 85% of the observed. Adding tidal forcing has a minimal impact on the surface circulation but increases the deep EKE by 12% and the deep KEM by 25%. Doubling the horizontal resolution of the model increases the surface EKE to levels comparable to the drifter observations and increases the KEM by 40%, which is greater than the drifter estimates. The deep EKE and KEM also are increased to levels consistent with the deep current meters. Data assimilation increases the surface EKE to levels consistent with the drifter observations and increases the deep EKE and KEM. Surprisingly, data assimilation weakens the KEM at the surface and upper thermocline to levels below the 1/12° simulation.

22. Mean Kinetic Energy at Surface (cm 2 /s 2 ) Kinetic Energy of the Mean Flow at the Surface 1/12° Drifters

23. Large Scale Prediction GOFS V3.5 Maximenko and Niiler 1/25° non-assim. global HYCOM Mean SSH 2004-2009

24. Large Scale Prediction GOFS V3.5 1/25° non-assim. global HYCOM 1/12° non-assim. global HYCOM Mean SSH 2004-2009 Forced with 0.5° NOGAPS winds and heat fluxes

25. Large Scale Prediction GOFS V3.5 1/25° non-assim. global HYCOM 1/12° non-assim. global HYCOM SSH Variability (cm) 2004-2009 Satellite observations from CLS