The Hybrid Ocean Modeling Environment The Hybrid Ocean Modeling Environment (HOME)(HOME)

A vision for Community Ocean Circulation Models:A vision for Community Ocean Circulation Models:Generalized Vertical CoordinatesGeneralized Vertical Coordinates

Presented on behalf of the HOME Team:Presented on behalf of the HOME Team:

R. Hallberg, R. Bleck, E. Chassignet, R. deSzoeke, S. R. Hallberg, R. Bleck, E. Chassignet, R. deSzoeke, S. Griffies, P. Schopf, S. Springer and A. WallcraftGriffies, P. Schopf, S. Springer and A. Wallcraft

The HOME white paper advocates:The HOME white paper advocates:

•Development: A Development: A versatile, open-versatile, open-source, community Ocean Modeling source, community Ocean Modeling Environment using a generalized Environment using a generalized hybrid vertical coordinatehybrid vertical coordinate..

•Science: Study Science: Study best practicesbest practices for for modeling various important oceanic modeling various important oceanic phenomena.phenomena.

The 10-year VisionThe 10-year Vision• Precursor ocean models disappear.Precursor ocean models disappear.

• Artificial fault lines of ocean modeling Artificial fault lines of ocean modeling community based on vertical coordinate (community based on vertical coordinate ( vs. Z vs. vs. Z vs. ) are erased.) are erased.

• The same ocean modeling codes usable for The same ocean modeling codes usable for education, research, and operations.education, research, and operations.

• Open, international, and multi-disciplinaryOpen, international, and multi-disciplinary..

What is a “Modeling What is a “Modeling Environment”?Environment”?A “Model”:A “Model”:• A specific collection of algorithms –A specific collection of algorithms –

e.g. MICOM v2.8e.g. MICOM v2.8- or -- or -• A specific configuration, including parameter A specific configuration, including parameter

settings, geometry, forcing fields, etc. –settings, geometry, forcing fields, etc. –e.g. The 1/12e.g. The 1/12°° North Atlantic MICOM model North Atlantic MICOM model

A “Modeling Environment”:A “Modeling Environment”:• Uniform code comprising a diverse collection Uniform code comprising a diverse collection

of interchangeable algorithms and supporting of interchangeable algorithms and supporting software from which a model can be selected.software from which a model can be selected.

zz σσ-z-z

σσ HybridHybrid

What are hybrid coordinates?What are hybrid coordinates?

There is broad agreement among ocean There is broad agreement among ocean modelers that generalized vertical coordinates modelers that generalized vertical coordinates are desirable.are desirable.

A large fraction of the U.S. ocean model A large fraction of the U.S. ocean model development community will therefore development community will therefore participate in HOME development.participate in HOME development.• HOME Predecessor Models:HOME Predecessor Models:

– HIM (NOAA/GFDL)HIM (NOAA/GFDL)– HYCOM (U. Miami, Navy NRL, & DOE LANL)HYCOM (U. Miami, Navy NRL, & DOE LANL)– HYPOP (DOE LANL)HYPOP (DOE LANL)– Poseidon (NASA/GMAO & George Mason U.)Poseidon (NASA/GMAO & George Mason U.)– POSUM (Oregon State U.)POSUM (Oregon State U.)

• Contributing Models:Contributing Models:– MITgcm (MIT) – A. AdcroftMITgcm (MIT) – A. Adcroft– MOM4 (NOAA/GFDL) – S. GriffiesMOM4 (NOAA/GFDL) – S. Griffies– ROMS (Rutgers U. & UCLA) – D. Haidvogel, J. ROMS (Rutgers U. & UCLA) – D. Haidvogel, J.

McWilliams, A. ShchepetkinMcWilliams, A. Shchepetkin

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

variabilityvariability

Examples of HOME predecessor model Examples of HOME predecessor model applications:applications:

Tropical Instability Waves in an ENSO forecastTropical Instability Waves in an ENSO forecast

Examples of HOME predecessor model applications:Examples of HOME predecessor model applications:1/121/12°° Pacific HYCOM with regional nesting Pacific HYCOM with regional nesting

Forced with high frequency ECMWF winds and thermal forcingForced with high frequency ECMWF winds and thermal forcingSSH Snapshot – 21 MarchSSH Snapshot – 21 March

Examples of HOME predecessor model Examples of HOME predecessor model applications:applications:

Mediterranean Overflow into an Atlantic ModelMediterranean Overflow into an Atlantic Model

Examples of HOME predecessor model Examples of HOME predecessor model applications:applications:

Global climate simulations at NASA/GISSGlobal climate simulations at NASA/GISS

HOME would be a joint effort of several HOME would be a joint effort of several Federal Agencies (NOAA, Navy/NRL, Federal Agencies (NOAA, Navy/NRL, NASA, DOE) and university groups, with a NASA, DOE) and university groups, with a structure that invites contributions from structure that invites contributions from the broader domestic and international the broader domestic and international community.community.

HOME could be construed to partially HOME could be construed to partially address Rec. 28-2 of the U.S. Commission address Rec. 28-2 of the U.S. Commission on Ocean Policy Report:on Ocean Policy Report:

““NOAA and the U.S. Navy should establish a joint ocean and NOAA and the U.S. Navy should establish a joint ocean and coastal information management and communications coastal information management and communications program… [that] should create a research and development program… [that] should create a research and development component…to generate new models and forecasts in component…to generate new models and forecasts in collaboration with Ocean.IT, taking full advantage of the collaboration with Ocean.IT, taking full advantage of the expertise found in academia and the private sector.”expertise found in academia and the private sector.”

Advantages of HOME: Community Advantages of HOME: Community CohesionCohesion• An organic trust-base already exists An organic trust-base already exists

within the Lagrangian-vertical-within the Lagrangian-vertical-coordinate ocean modeling community.coordinate ocean modeling community.

• All major developers recognize the All major developers recognize the practical benefits from trading “code practical benefits from trading “code ownership” for “community modeling”ownership” for “community modeling”– Reduced redundancy of effortsReduced redundancy of efforts– Increased collaborations and intellectual cross-Increased collaborations and intellectual cross-

fertilizationfertilization– Increased capabilities available to all researchers Increased capabilities available to all researchers

and applicationsand applications– More rapid solution of common difficultiesMore rapid solution of common difficulties

Advantages of HOME: Advantages of HOME: IngenuityIngenuity

• More rapid model improvementsMore rapid model improvements

• Combine existing capabilities of predecessor Combine existing capabilities of predecessor models to identify optimal configurationsmodels to identify optimal configurations

• Provide a target for new developments to be Provide a target for new developments to be rapidly evaluated and transitioned to realistic rapidly evaluated and transitioned to realistic ocean model applications.ocean model applications.

• Enable direct comparison of new techniques Enable direct comparison of new techniques with existing in idealized and actual applicationswith existing in idealized and actual applications

Biological metaphor: “Breed” better ocean models Biological metaphor: “Breed” better ocean models from a bigger “gene pool” of algorithms.from a bigger “gene pool” of algorithms.

Advantages of HOME: Advantages of HOME: TechnologyTechnology

• Built upon ESMF & Built upon ESMF & PRISM standardsPRISM standards

• Single code-base Single code-base readily deployable to readily deployable to a wide variety of a wide variety of computer computer architecturesarchitectures

• Facilitates long-term Facilitates long-term support & stabilitysupport & stability

• ESMF adoption ESMF adoption provides a window of provides a window of opportunity when the opportunity when the transition to HOME transition to HOME will be less disruptive.will be less disruptive.

ESMF Infrastructure(Low-level utilities)

SelectedHOME Code

ESMF or PRISM Superstructure

External Hardware libraries, MPI, NetCDF, …

Advantages of HOME: Advantages of HOME: TechnologyTechnology

• Built upon ESMF & Built upon ESMF & PRISM standardsPRISM standards

• Single code-base Single code-base readily deployable to readily deployable to a wide variety of a wide variety of computer computer architecturesarchitectures

• Facilitates long-term Facilitates long-term support & stabilitysupport & stability

• ESMF adoption ESMF adoption provides a window of provides a window of opportunity when the opportunity when the transition to HOME transition to HOME will be less disruptive.will be less disruptive.

ESMF Infrastructure(Low-level utilities)

SelectedHOME Code

ESMF or PRISM Superstructure

External Hardware libraries, MPI, NetCDF, …

AGCM

Advantages of HOME: Advantages of HOME: EducationEducation

• Students would learn about using ocean Students would learn about using ocean models with the same code-base as is models with the same code-base as is widely used for real applications.widely used for real applications.

• The HOME code will allow for easy-to-The HOME code will allow for easy-to-use, pedagogically interesting examples.use, pedagogically interesting examples.

• Code will be adaptable for a wide variety Code will be adaptable for a wide variety of student research topics.of student research topics.

A Science VisionA Science Vision

•IPCC-class climate IPCC-class climate simulationssimulations

•Biogeochemical simulationsBiogeochemical simulations

•Pelagic-to-coastal integrationPelagic-to-coastal integration

•Ocean data assimilationOcean data assimilation

HOME and Climate modelingHOME and Climate modeling• Hybrid-isopycnal coordinate HOME-predecessor models Hybrid-isopycnal coordinate HOME-predecessor models

are being used for IPCC at NASA/GISS and NOAA/GFDL.are being used for IPCC at NASA/GISS and NOAA/GFDL.– Most coupled climate models have traditionally used Most coupled climate models have traditionally used

Z-coordinates, leading to common biasesZ-coordinates, leading to common biases..– Multiple types of viable climate models will be Multiple types of viable climate models will be

enormously powerful for evaluating robustness.enormously powerful for evaluating robustness.

• Dense overflows mediate many climatically important Dense overflows mediate many climatically important slow processes (e.g. North Atlantic thermohaline slow processes (e.g. North Atlantic thermohaline circulation). Controlling the level and location of circulation). Controlling the level and location of diapycnal diffusion in overflows is of particularly diapycnal diffusion in overflows is of particularly importance for long climate simulations.importance for long climate simulations.

• Eddy-permitting models using Z-coordinates exhibit Eddy-permitting models using Z-coordinates exhibit large advective diapycnal watermass modification large advective diapycnal watermass modification (Griffies et al., MWR, 2000). Isopycnal coordinates may (Griffies et al., MWR, 2000). Isopycnal coordinates may prove uniquely useful for eddy-permitting climate prove uniquely useful for eddy-permitting climate simulations.simulations.

PhysicalModel

Nitrate[NO3]

Advection& Mixing

SmallPhytoplankton

[P1]NO3

Uptake

Micro-Zooplankton

[Z1]

Grazing

Ammonium[NH4]

Excretion

NH4

Uptake

Detritus-N[DN]

FecalPellet

Sinking

Silicate[Si(OH)4]

Diatoms[P2]

SiUptake

N-Uptake

Meso-Zooplankton

[Z2]

Sinking

Detritus-Si[DSi]

GrazingFecalPellet

Sinking

Predation

Lost

Total CO2

[TCO2]

BiologicalUptake

Air-Sea Exchange

Physical-Biogeochemical Model: Fei Chai

HOME and Biogeochemical HOME and Biogeochemical modelingmodeling

Biogeochemical modeling places unique demands Biogeochemical modeling places unique demands on ocean models:on ocean models:

• Use lots of tracersUse lots of tracers– Typically evolve more slowly than internal gravity Typically evolve more slowly than internal gravity

waveswaves– The HOME techniques allow very clean separation of The HOME techniques allow very clean separation of

tracer time stepping from dynamics.tracer time stepping from dynamics.– GFDL/HIM is GFDL/HIM is ~10 times faster~10 times faster than GFDL/MOM4 in 1° than GFDL/MOM4 in 1°

global models with 20 tracers and same number of global models with 20 tracers and same number of layers!layers!

• Depend strongly on material conservation of Depend strongly on material conservation of propertiesproperties– Isopycnal coordinate models ability to control diapycnal Isopycnal coordinate models ability to control diapycnal

diffusion is invaluable.diffusion is invaluable.

Examples of HOME predecessor model applications:Examples of HOME predecessor model applications:1/25° East Asian Seas HYCOM (nested inside 1/61/25° East Asian Seas HYCOM (nested inside 1/6°° Pacific) Pacific)

North-south velocity cross-section along 124.5°E, upper 400 mNorth-south velocity cross-section along 124.5°E, upper 400 m

Snapshot on 14 October

density frontdensity frontassociated withassociated with

sharp topographic featuresharp topographic feature(cannot be resolved with(cannot be resolved with

fixed coordinates)fixed coordinates)

red=eastward flowblue=westward flow

East China East China SeaSea

Yellow Sea flowreversal with depth

Isopycnals overshelf region

z-levels and sigma-levelsover shelf and in mixed layer

Snapshot on 12 April

YellowYellow SeaSea

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

Coastal applications of HOMECoastal applications of HOME

• HOME predecessor models already work in HOME predecessor models already work in coastal applicationscoastal applications

• HOME offers the prospect of moving from HOME offers the prospect of moving from the blue-water into the coastal zones the blue-water into the coastal zones seamlessly.seamlessly.

• Nesting, open boundary conditions, and Nesting, open boundary conditions, and data assimilation capabilities have been data assimilation capabilities have been used successfully.used successfully.

• Key coastal model developers (J. Key coastal model developers (J. McWilliams, D. Haidvogel, A. Shchepetkin) McWilliams, D. Haidvogel, A. Shchepetkin) have agreed to collaborate in making world-have agreed to collaborate in making world-class HOME-based coastal models.class HOME-based coastal models.

HOME and Ocean Data HOME and Ocean Data AssimilationAssimilation

• Several HOME predecessors have Several HOME predecessors have demonstrated value from multiple data demonstrated value from multiple data assimilation approaches.assimilation approaches.– Optimal Interpolation ; EnVOI ; EnKF ; SEEK ; Optimal Interpolation ; EnVOI ; EnKF ; SEEK ;

ROIF ; AdjointROIF ; Adjoint

• HOME will be a natural host for this collection HOME will be a natural host for this collection of methodologies.of methodologies.

• Some data assimilation techniques require a Some data assimilation techniques require a tangent linear model and adjoint of the tangent linear model and adjoint of the forward model, which can be naturally forward model, which can be naturally incorporated in the framework.incorporated in the framework.

The 10-year RoadmapThe 10-year Roadmap• Distinct HOME predecessor codes disappear within Distinct HOME predecessor codes disappear within

3-5 years.3-5 years.• HOME group will have extensive consultation with HOME group will have extensive consultation with

European and other international counterparts European and other international counterparts (e.g. NEMO)(e.g. NEMO)

• Strong coordination with existing Z- and Strong coordination with existing Z- and - - modeling groups over 3-5 years sets the stage for modeling groups over 3-5 years sets the stage for next step.next step.

• Broad unification of all ocean model development Broad unification of all ocean model development activities within a generalized ocean modeling activities within a generalized ocean modeling environment over 10 years.environment over 10 years.

• Algorithmic diversity will persist, with the selection Algorithmic diversity will persist, with the selection dictated by the needs of specific applications.dictated by the needs of specific applications.

HOME Measures of Success HOME Measures of Success (1)(1)

• Voluntary participation of existing isopycnal Voluntary participation of existing isopycnal & hybrid ocean model community& hybrid ocean model community in in developing a common ocean modeling developing a common ocean modeling environment.environment.

• Collaboration from the broader ocean model Collaboration from the broader ocean model development communitydevelopment community, especially in the , especially in the extension of HOME to applications that have extension of HOME to applications that have not traditionally used isopycnal coordinates.not traditionally used isopycnal coordinates.

• Contributions of new capabilitiesContributions of new capabilities from from beyond the circle of developers of existing beyond the circle of developers of existing models.models.

HOME Measures of Success HOME Measures of Success (2)(2)

• A A code basecode base that is easy to configure and that is easy to configure and use for a variety of applications, with use for a variety of applications, with clear, consistent, and explicit clear, consistent, and explicit documentationdocumentation

• Widespread adoptionWidespread adoption of the HOME code- of the HOME code-base for ocean applicationsbase for ocean applications

• Useful and extensive Useful and extensive best-practice best-practice guidanceguidance for HOME users for HOME users

• Pedagogically useful examplesPedagogically useful examples derived derived from the HOME code basefrom the HOME code base

-- Rotating and stratified fluidsRotating and stratified fluids =>=> dominance of dominance of lateral over vertical transport. lateral over vertical transport.

-- Hence, it is traditional in ocean modeling to orient 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 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 designdesign (DYNAMO, DAMÉE-NAB). (DYNAMO, DAMÉE-NAB).

-- The practical issues of representation and The practical issues of representation and parameterization are often directly linked to the parameterization are often directly linked to the vertical coordinate choicevertical coordinate choice (Griffies et al., 2000).(Griffies et al., 2000).

Why does the vertical coordinate Why does the vertical coordinate matter so much?matter so much?

• Properties of the ocean:Properties of the ocean:– HydrostaticHydrostatic– AdiabaticAdiabatic– Rotating and density stratified Rotating and density stratified – Surface forcedSurface forced– Constrained by bathymetryConstrained by bathymetryConsequences: Conservative of PV, tracers, Consequences: Conservative of PV, tracers,

momentum, etc.momentum, etc.

• The vertical coordinate strongly affects the The vertical coordinate strongly affects the ability of a numerical model to respect ability of a numerical model to respect these properties, and to parameterize these properties, and to parameterize unresolved physical processes.unresolved physical processes.

Currently, there areCurrently, there are three main vertical coordinates three main vertical coordinates in use, none of which provides universal utility. in use, none of which provides universal utility.

Hence, many developers have been motivated to Hence, many developers have been motivated to pursue research intopursue research into hybrid approaches.hybrid approaches.

Currently, there areCurrently, there are three main vertical coordinates three main vertical coordinates in use, none of which provides universal utility. in use, none of which provides universal utility.

Hence, many developers have been motivated to Hence, many developers have been motivated to pursue research intopursue research into hybrid approaches.hybrid approaches.