1. The Hybrid Ocean Modeling Environment (HOME) A vision for Community Ocean Circulation Models: Generalized Vertical Coordinates Presented on behalf of the HOME Team: R. Hallberg, R. Bleck, E. Chassignet, R. deSzoeke, S. Griffies, P. Schopf, S. Springer and A. Wallcraft

2. What is a “Modeling Environment”? A “Model”: A specific collection of algorithms – e.g. MICOM v2.8 A specific collection of algorithms – e.g. MICOM v2.8 - or - A specific configuration, including parameter settings, geometry, forcing fields, etc. – e.g. The 1/12° North Atlantic MICOM model A specific configuration, including parameter settings, geometry, forcing fields, etc. – e.g. The 1/12° North Atlantic MICOM model A “Modeling Environment”: Uniform code comprising a diverse collection of interchangeable algorithms and supporting software from which a model can be selected. Uniform code comprising a diverse collection of interchangeable algorithms and supporting software from which a model can be selected.

3. - Rotating and stratified fluids => dominance of lateral over vertical transport. lateral over vertical transport. - Hence, it is traditional in ocean modeling to orient the two horizontal coordinates orthogonal to the the two horizontal coordinates orthogonal to the local vertical direction as determined by gravity. local vertical direction as determined by gravity. - The choice of the vertical coordinate system is the single most important aspect of an ocean model's single most important aspect of an ocean model's design (DYNAMO, DAMÉE-NAB). design (DYNAMO, DAMÉE-NAB). - The practical issues of representation and parameterization are often directly linked to the parameterization are often directly linked to the vertical coordinate choice (Griffies et al., 2000). vertical coordinate choice (Griffies et al., 2000).

4. Currently, there are three main vertical coordinates in use, none of which provides universal utility. Hence, many developers have been motivated to pursue research into hybrid approaches.

5. Vertical Coordinates Vertical Coordinates

6. z σ-z σHybrid

7. The hybrid coordinate in HYCOM is isopycnal in the open, stratified ocean, but smoothly reverts to a terrain- following coordinate in shallow coastal regions, and to pressure coordinate in the mixed layer and/or unstratified seas.

8. Examples of HOME predecessor model applications: 1/25° East Asian Seas HYCOM (nested inside 1/6° Pacific) North-south velocity cross-section along 124.5°E, upper 400 m Snapshot on 14 October density front associated with sharp topographic feature (cannot be resolved with fixed coordinates) red=eastward flowblue=westward flow East China Sea Yellow Sea flow reversal with depth Isopycnals over shelf region z-levels and sigma-levels over shelf and in mixed layer Snapshot on 12 April YellowSea

9. There is broad agreement among ocean modelers that generalized coordinates are desirable. A large fraction of the U.S. ocean model development community will therefore participate in HOME development. HOME Predecessor Models: HOME Predecessor Models: –HIM (NOAA/GFDL) –HYCOM (U. Miami, Navy NRL, & DOE LANL) –HYPOP (DOE LANL) –Poseidon (NASA/GISS & George Mason U.) –POSUM (Oregon State U.) Contributing Models: Contributing Models: –MITgcm (MIT) – A. Adcroft –MOM4 (NOAA/GFDL) – S. Griffies –ROMS (Rutgers U. & UCLA) – D. Haidvogel, J. McWilliams, A. Shchepetkin

10. Examples of HOME predecessor model applications: Studies of the role of resolution and eddies in climate variability

11. Examples of HOME predecessor model applications: Tropical Instability Waves in an ENSO forecast

12. Examples of HOME predecessor model applications: 1/12° Pacific HYCOM with regional nesting Forced with high frequency ECMWF winds and thermal forcing SSH Snapshot – 21 March

13. Examples of HOME predecessor model applications: Overflows? (Papadakis et al or other?)

14. Examples of HOME predecessor model applications: Global climate simulations at NASA/GISS

15. The HOME white paper advocates the development of a versatile, open-source, community Ocean Modeling Environment using a generalized hybrid vertical coordinate. In addition to collecting the common code base, HOME would identify best practices for modeling key oceanic phenomena.

16. HOME would be a joint effort of several Federal Agencies (NOAA, ONR, NASA, DOE) and university groups, with a structure that invites contributions from the broader domestic and international community. HOME could be construed to partially address Rec. 28-2 of the U.S. Commission on Ocean Policy Report: “NOAA and the U.S. Navy should establish a joint ocean and coastal information management and communications program… [that] should create a research and development component…to generate new models and forecasts in collaboration with Ocean.IT, taking full advantage of the expertise found in academia and the private sector.”

17. Advantages of HOME: Community Cohesion An organic trust-base already exists within the Lagrangian-vertical-coordinate ocean modeling community. An organic trust-base already exists within the Lagrangian-vertical-coordinate ocean modeling community. All major developers recognize the practical benefits from trading “code ownership” for “community modeling” All major developers recognize the practical benefits from trading “code ownership” for “community modeling” –Reduced redundancy of efforts –Increased collaborations and intellectual cross-fertilization –Increased capabilities available to all researchers and applications –More rapid solution of common difficulties

18. Advantages of HOME: Ingenuity More rapid model improvements More rapid model improvements Combine existing capabilities of predecessor models to identify optimal configurations Combine existing capabilities of predecessor models to identify optimal configurations Provide a target for new developments to be rapidly evaluated and transitioned to realistic ocean model applications. Provide a target for new developments to be rapidly evaluated and transitioned to realistic ocean model applications. Enable direct comparison of new techniques in idealized and actual applications Enable direct comparison of new techniques in idealized and actual applications Biological metaphor: “Breed” better ocean models from a bigger “gene pool” of algorithms.

19. Advantages of HOME: Technology Built upon ESMF & PRISM standards Built upon ESMF & PRISM standards Single code-base readily deployable to a wide variety of computer architectures Single code-base readily deployable to a wide variety of computer architectures Facilitates long-term support & stability Facilitates long-term support & stability Window of opportunity: ESMF adoption Window of opportunity: ESMF adoption Low Level Utilities Fields and Grids Layer Model Layer Components Layer: Gridded Components Coupler Components ESMF Infrastructure Selected HOME Code ESMF or PRISM Superstructure BLAS, MPI, NetCDF, … External Libraries

20. Advantages of HOME: Flexibility Enable a single modeling system to be tailored for the demands of a particular application. Enable a single modeling system to be tailored for the demands of a particular application. Atmospheric and oceanic applications have shown the versatility of generalized coordinates. Atmospheric and oceanic applications have shown the versatility of generalized coordinates.

21. Advantages of HOME: Education The HOME code base will allow for easy to use pedagogically interesting examples. The HOME code base will allow for easy to use pedagogically interesting examples. Adaptable for a variety of research Adaptable for a variety of research

22. Coastal applications of HOME HOME predecessor models already work in coastal applications HOME predecessor models already work in coastal applications HOME offers the prospect of moving from the blue-water into the coastal zones seamlessly. HOME offers the prospect of moving from the blue-water into the coastal zones seamlessly. Nesting, open boundary conditions, and data assimilation capabilities have been used successfully. Nesting, open boundary conditions, and data assimilation capabilities have been used successfully. Key coastal model developers (J. McWilliams, D. Haidvogel, A. Shchepetkin) have agreed to collaborate in making world-class HOME-based coastal models. Key coastal model developers (J. McWilliams, D. Haidvogel, A. Shchepetkin) have agreed to collaborate in making world-class HOME-based coastal models.

23. Physical Model Nitrate [NO 3 ] Advection & Mixing Small Phytoplankton [P1] NO 3 Uptake Micro- Zooplankton [Z1] Grazing Ammonium [NH 4 ] Excretion NH 4 Uptake Detritus-N [DN] Fecal Pellet Sinking Silicate [Si(OH) 4 ] Diatoms [P2] Si Uptake N-Uptake Meso- Zooplankton [Z2] Sinking Detritus-Si [DSi] Grazing Fecal Pellet Sinking Predation Lost Total CO 2 [TCO 2 ] Biological Uptake Air-Sea Exchange Physical-Biogeochemical Model: Fei Chai

24. HOME and Biogeochemical modeling Biogeochemical modeling places unique demands on ocean models: Use lots of tracers Use lots of tracers –Typically evolve with slower timescales than internal gravity waves –Lagrangian-vertical coordinate solution techniques allow very clean separation of tracer time stepping from dynamics. –GFDL/HIM is ~10 times faster than GFDL/MOM4 with 20 tracers! Depend strongly on material conservation of properties Depend strongly on material conservation of properties –Isopycnal coordinate models ability to control diapycnal diffusion is invaluable.

25. HOME and Climate modeling HOME-predecessor models are under active consideration for IPCC use at NOAA/GFDL & NASA/GISS. Most coupled climate models have traditionally used Z-coordinates, leading to common biases. HOME-predecessor models are under active consideration for IPCC use at NOAA/GFDL & NASA/GISS. Most coupled climate models have traditionally used Z-coordinates, leading to common biases. Dense overflows mediate many climatically important slow processes (e.g. North Atlantic thermohaline circulation). Controlling the level of diapycnal diffusion in overflows is of particular importance for long climate simulations. Dense overflows mediate many climatically important slow processes (e.g. North Atlantic thermohaline circulation). Controlling the level of diapycnal diffusion in overflows is of particular importance for long climate simulations. Eddy-permitting models using Z-coordinates exhibit large advective diapycnal watermass modification (Griffies et al., MWR, 2000). Isopycnal coordinate may prove uniquely useful for eddy-permitting climate simulations. Eddy-permitting models using Z-coordinates exhibit large advective diapycnal watermass modification (Griffies et al., MWR, 2000). Isopycnal coordinate may prove uniquely useful for eddy-permitting climate simulations.

26. HOME and Ocean Data Assimilation Some HOME predecessors have demonstrated value from multiple data assimilation approaches. Some HOME predecessors have demonstrated value from multiple data assimilation approaches. –Optimal Interpolation ; EnVOI ; EnKF ; SEEK ; ROIF ; Adjoint The Ocean Modeling Environment will be a natural host for this collection of algorithms. The Ocean Modeling Environment will be a natural host for this collection of algorithms. Some of the data assimilation techniques require a linear tangent and adjoint of the forward model, which can be naturally incorporated in the framework. Some of the data assimilation techniques require a linear tangent and adjoint of the forward model, which can be naturally incorporated in the framework.

27. The 10-year vision Distinct HOME predecessor codes disappear within 3-5 years. Distinct HOME predecessor codes disappear within 3-5 years. HOME group will have extensive consultation with European and other international counterparts (NEMO) HOME group will have extensive consultation with European and other international counterparts (NEMO) Strong coordination with existing Z- and  - modeling groups over 3-5 years sets the stage for next step. Strong coordination with existing Z- and  - modeling groups over 3-5 years sets the stage for next step. Broad unification of all ocean model development activities within a generalized ocean modeling environment over 10 years. Broad unification of all ocean model development activities within a generalized ocean modeling environment over 10 years. Diversity will persist within the environment with a choice of algorithms for various applications. Diversity will persist within the environment with a choice of algorithms for various applications.

28. HOME Measures of Success (1) Voluntary participation of existing isopycnal & hybrid ocean model community in developing a common ocean modeling environment. Voluntary participation of existing isopycnal & hybrid ocean model community in developing a common ocean modeling environment. Collaboration from the broader ocean model development community, especially in the extension of HOME to applications that have not traditionally used isopycnal coordinates. Collaboration from the broader ocean model development community, especially in the extension of HOME to applications that have not traditionally used isopycnal coordinates. Contributions of new capabilities from beyond the circle of developers of existing models. Contributions of new capabilities from beyond the circle of developers of existing models.

29. HOME Measures of Success (2) A code base that is easy to configure and use for a variety of applications, with clear, consistent, and explicit documentation A code base that is easy to configure and use for a variety of applications, with clear, consistent, and explicit documentation Widespread adoption of the HOME code- base for ocean applications. Widespread adoption of the HOME code- base for ocean applications. Useful and extensive best-practice guidance for HOME users. Useful and extensive best-practice guidance for HOME users. Pedagogically useful examples derived from the HOME code base. Pedagogically useful examples derived from the HOME code base.