Report to WGOMD on GFDL Ocean Modelling Activities 20042005

1
Report to WGOMD on GFDL Ocean Modelling
Activities 2004-2005

• Stephen Griffies
• NOAA/GFDL (and CSIRO)

• IPCC AR4 activities
• Model developments

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IPCC activities

• Completed development of AR4 coupled climate
  model in 2004, and submitted simulations to PCMDI
  2004/2005.
• 1 degree ocean (mom4) with 50 levels and 1/3
  degree at equator. Described at previous
  meetings.
• Numerous studies now being conducted to document
  the models design and simulation
  characteristics. Will take years to fully
  evaluate.

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GFDL Coupled Model results
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References
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Ocean Model
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• Plans for GFDL ocean model development
• A briefing to WGOMD

• Inform WGOMD of plans for MOM4 over next 6
  months
• Speculate on 3-5 years research/development goals
  and
• applications involving ocean models.

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MOM4 as of November 2005

• Four public releases
• MOM4p0a Jan2004
• MOM4p0b Mar2004
• MOM4p0c Oct2004
• MOM4p0d May2005
• Roughly 300 registered users from 30 countries
  using 35 computational platforms. They
  represent about 1200 scientists, engineers, and
  programmers using the code and simulation results
  for research and development.

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MOM4 user statistics
Vertical lines are intermediate code
releases mom4p0a mom4p0b mom4p0c mom4p0d
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GFDL Applications of MOM4

• IPCC Global climate change modelling
• Ocean component to the GFDL AR4 climate change
  models.
• Developed largely for global climate modeling
  applications.
• 50 GFDL scientists directly involved with this
  research and development.
• Earth system modelling
• interactive land, atmosphere, ocean
  biogeochemistry and ecosystems
• 30 scientists at GFDL and Princeton University
• Global and regional process studies
• paleo-oceanography
• idealized climate change simulations
• thermohaline shutdown
• physical process studies
• 20 scientists, visiting researchers, post-docs,
  graduate students

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Gravity current-entrainment CPT
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Eddy mixed layer interactions CPT
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MOM4p1 vertical coordinate features
free surface z-model mom4p0

• Terrain following s-model
• Smooth topography
• Regular computational domain (no land/sea masks)
• Time independent computational domain
• (-1 lt sigma lt 0)
• Pressure gradient errors requires topography
  filters
• Difficult neutral physics
• implementation not commonly done in sigma-models

• Partial step topography
• Trivial pressure gradient errors
• Decades of experience
• Well known limitations
• Irregular and variable computational domain
• (i.e., land/sea masks and
• vanishing surface layer)

• Irregular computational domain
• (i.e., land/sea masks needed)
• Time independent computational
• domain (-H lt z lt 0) no vanishing layers.
• Negligible pressure gradient errors since
  isosurfaces are quasi-horizontal.
  Correspondingly, can use the same neutral physics
  technology as in z-models.

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Evolution of GFDL ocean codes

• Evolution is in response to many inputs
• New applications
• Refined resolution climate models
• Biogeochemistry and ecosystem applications
• Earth system modeling
• Coastal impacts of climate change
• Non-hydrostatic processes at very refined
  resolutions
• Enhanced features
• physical parameterizations (e.g., mixed layers,
  mesoscale eddies)
• algorithm fundamentals (e.g., time stepping,
  vertical coordinates)
• better understanding of the ocean (e.g., equation
  formulations)
• Computational efficiency and platform portability
• Input from the international user communities
  (HIM, MITgcm, MOM4)
• Main developers Alistair Adcroft, Bob Hallberg,
  Steve Griffies

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Evolution Path

• MOM4p1 March 2006 with rudimentary generalized
  vertical coordinate features to expand mom4
  applications.
• HIM-Fortran Hallberg Isopycnal Model, publicly
  supported within GFDL Flexible Modeling System
  (FMS) GFDL development now aimed at coupled
  simulations to compare w/ mom4-based coupled
  model.
• Research Merge three fundamental perspectives
• non-hydrostatic z-modeling from MIT (Adcroft)
• hydrostatic isopycnal modeling from HIM
  (Hallberg)
• Global ocean climate modeling from MOM4
  (Griffies)
• Key NOAA application climate impacts on coasts
• Global BackBone Model 10 km with nest to 1 km
• Tides, wave breaking, storm surge, sediment
  transport, etc.
• 2008-2010 for first public code release

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Horizontal grids nesting and cubed sphere

• Multiple 2-way nested regions
• Mass and tracer conservation Most nesting
  implementations in ocean and atmospheric models
  are non-conservative
• Time sub-cycling coarse region not constrained
  by time step used in fine region. Essential for
  economical global models with nests.
• Envision applications in areas such as
• global climate models boundaries, choke points,
  etc.
• Regional modeling with nests to estuary scale
• Coastal biogeochemistry and ecosystems
• Present development
• general grid description
• tools for parallel computing and coupled
  modeling
• analysis/visualization tools
• shallow water test cases
• Cubed Sphere
• technology from MITgcm
• Also envisioned for finite volume atmosphere model

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Main Applications

• Coastal impacts of climate change
• Earth System Modelling w/ eddying simulations
  (1/3 to 1/4 degree mercator with twoway nesting
  in selected critical regions)
• NOAA BackBone model, with 1/10 global to be
  nested with finer grids in certain coastal areas.
  For use by many projects within NOAA.
• nonHydrostatic process studies and very refined
  coastal and estuary simulations
• University PI and student research and education

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HIM MIT MOM ???
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Unified GFDL Ocean Code

• Bring together our understanding of the ocean and
  how to simulate a wide range of scales.
• Various algorithms with stepwise evolution
  involving suites of applications to test methods
  and flesh out favourable approaches.
• This effort is a major research and development
  project, presently in its early stages at GFDL.
  Much research remains to determine particulars of
  algorithms.
• Various efforts (e.g., HOME) to develop a US
  community model have failed to garner funds. GFDL
  is committed to this project using in-house
  resources, and will involve outside collaborators
  as best as possible.