Report from Working Group for Ocean Model Development WGOMD

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Report from Working Group for Ocean Model
Development (WGOMD)
Panel members S. Griffies (chair), H. Banks
(proposed co-chair), G. Danabasoglu, H. Drange,
M. England, R. Greatbatch, G. Madec, H. Tsujino
Emeritus C. Boening, E. Chassignet, R. Gerdes,
A.-M. Treguier CLIVAR rep Anna Pirani
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WGOMD Terms of Reference (as of 2005)

• To stimulate the development of ocean models for
  research in climate and related fields.
• To encourage investigations of the effects of
  model formulation on the results of ocean models,
  making use of sensitivity studies and
  intercomparisons.
• To promote interaction amongst the ocean
  modelling community and between this and other
  communities through workshops and other
  activities.
• To stimulate the validation of ocean models when
  used in stand alone mode and as part of a coupled
  ocean-atmosphere model, using oceanographic data
  and other methods, and to advise on the
  observational requirements of such studies.
• To publicise developments in ocean models amongst
  the climate modelling community.
• To collaborate with other activities in areas of
  overlapping responsibility.
• To advise on ocean modelling and related issues
  and to report on its activities to the JSC/CLIVAR
  WGCM and CLIVAR Scientific Steering Group.

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7th Panel meeting Bergen 25th-27th August 2007

• Organised numerical methods workshop before panel
  meeting, August 23-24
• 80 participants

• Discuss and debate novel methods for developing
  the next generation of ocean models for global,
  regional and coastal applications.
• Bring together key practitioners and algorithm
  developers for eight provocative and pedagogical
  sessions.

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7th Panel meeting Bergen 25th-26th August 2007

• Joint session with SOPHOCLES project
• Key discussions
• CORE (Coordinated Ocean Reference Experiments)
  design and progress
• Ocean metrics

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Key Goals of CORE

• Provide a workable and agreeable experimental
  design for global ocean-ice models to be run for
  long-term climate studies.
• Establish a framework where the experimental
  design is flexible and subject to refinement as
  the community gains experience and provides
  feedback.

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A Few Problems with Ocean-ice Modelling

• Diversity in Methods, lack of documentation
• Inconsistencies when decouple
• Decoupling ocean-ice from interactive
  atmosphere-land exposes the simulations to
  spurious instabilities and missed feedbacks,
  largely related to ambiguities in how to specify
  the hydrological cycle (e.g., mixed boundary
  conditions and THC stability).
• This problem leads to endless debates about SSS
  restoring (e.g., strength of the restoring
  normalization of hydrological cycle).
• These inconsistencies often do not cause
  large-scale problems until 100s of years, but
  when look in detail they may prove more
  problematic even for short-term.
• Ambiguity in Forcing
• Ocean surface fluxes are poorly known.
• Developing a global dataset for running ocean-ice
  models is very tough.
• Off-the-shelf reanalysis products are not
  balanced.
• Contrast to the well known SST, making AMIP seem
  trivial compared to OMIP.

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CORE is Not OMIP

• We do not term this an OMIP
• We are unprepared to formally sanction the
  present CORE protocol or forcing dataset until
  the community has time to provide feedback.
• CORE is a research project conducted by
  interested scientists.
• There is no oversight committee or repository of
  simulation output.
• An Ocean Model Intercomparison Project (OMIP) may
  evolve from CORE, but WGOMD is not prepared yet
  to make this recommendation, given the increased
  overhead of an OMIP, and continued evolution of
  the CORE experimental design.

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Atmospheric Dataset

• Large and Yeager (2004) Provide a balanced
  atmospheric state based on a hybrid of
• NCEP reanalysis
• Satellite products
• Adjustments
• Normal year is based on statistical average of 50
  year interannual data, plus sample synoptic
  variability.
• NCAR bulk formulae are used to compute fluxes
  based on prescribed atmospheric state and
  evolving SST and currents.
• Differences in bulk formulae yield large
  differences in fluxes, which then corrupt
  comparisons.
• Many caveats come with Large and Yeager (2004).
  Nonetheless,
• It continues to be refined based on new data and
  input from the modelling community.
• It is supported by two modelling centres (NCAR
  and GFDL).
• Hence, there is good reason for WGOMD to
  recommend its use for CORE.

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Three proposed COREs

• CORE-I 500 year spin-up with repeating Normal
  Year Forcing (NYF) (Griffies et al in
  preparation).
• CORE-II 50 year retrospective with interannually
  varying forcing (details of design under
  investigation by WGOMD and collaborators).
• CORE-III Fresh water melt perturbation
  idealizing the melt of water around Greenland
  (prototype documented by Gerdes, Hurlin, and
  Griffies 2006, Ocean Modelling)

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Progress with CORE-I

• Griffies et al. paper in preparation-21 authors
  from 11 institutions
• Project includes seven model groups with three
  ocean model classes (geopotential, isopycnal,
  hybrid).
• Other outcomes
• improved surface flux products
• discussions on bulk formulae

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Zonal Velocity at Equator Y491-500
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CORE-I sea ice
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CORE 1 Atlantic MOC at 45N
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CORE-II

• Hindcast type experiment with forcing varying
  from 1958-2004 (NCAR to update to 2006 by end of
  year)
• Experiments have already been performed by NCAR,
  DRAKKAR consortium
• Informal meeting will be arranged to coordinate
  community efforts
• Other outcomes
• Advice to GSOP on the best choice of surface
  forcing for ocean reanalysis

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Proposed collaboration with Pacific panel on
CORE-II (Magdalena Balmaseda)

• Known model deficiencies in representation of
  Pacific in climate models
• Upwelling off the South American Coast (winds,
  resolution?)
• Cold tongue penetrating too far west (winds?
  momentum mixing?)
• Too weak/too strong east-west slope of the
  thermocline
• Equatorial heat content (IT/meridional transport,
  vertical ..
• Pacific panel particularly interested in CORE-II
  experiments with additional sensitivity
  experiments to determine which are the dominant
  source of error
• Forcing fields?
• Model parameterizations/configuration?
• Model resolution?
• Parameterization of air-sea interaction?

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Ocean metrics

• WGOMD has started to set up a Repository for
  Evaluating Ocean Simulations (REOS)-digested
  summary of metrics, datasets, etc, with comments
  and recommendations.
• Ocean metrics are being developed by Hadley
  Centre, GSOP, GODAE, PCMDI
• At panel meeting, presentations on ocean metrics
  given by GSOP and Hadley Centre-how can we merge
  community efforts to a common standard?
• WGOMD intends to work to propose a suitable set
  of ocean metrics for model evaluation acceptable
  to the community, and in particular of use for
  AR5 ocean-ice.

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Key contributions of WGOMD

• Review paper Pedagogically documents
  state-of-art in ocean climate models (Griffies et
  al (2000))
• Workshops Topical workshops that facilitate
  collaboration, communication, and education
• Princeton/GFDL 2004 State-of-art in Ocean
  Climate Modelling
• Hobart/CSIRO 2005 Southern Ocean Modelling
• Bergen 2007 Numerical Methods for Ocean Models
• CORE Benchmark experiments for global ocean-ice
  models. Peer-review paper illustrates CORE-I with
  seven ocean-ice models each run for 500 years
  (Griffies et al in prep).

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Future plans

• We have plans for a CORE-II informal gathering
  within next 12 months, for those directly
  participating in the CORE-II experiments.
• WGOMD 8th panel meeting April 2009 at Hadley
  Centre
• WGOMD workshop on mesoscale eddies April 2009 at
  Hadley Centre

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GSOP proposed Metrics (Detlef Stammer)

• Systematic model-data comparison RMS model data
  differences rel. to prior data errors.
• Comparison to reference data sets, e.g., surface
  fluxes.
• Comparison with time series stations.
• Computation of integral quantities.
• Budgets, e.g., heat content and its change.
• Model-Model differences (incl. first guess).

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Hadley Centre Proposed ocean metrics

• Temperature (SST, X-secns, MLD)
• Salinity (SSS, X-secns)
• Currents (EUC, ACC, Arctic transports)
• Upwelling (Equatorial, Basin upwelling)
• Ocean transports (heat, freshwater)
• Water masses (T-S, formation)
• Budgets (conservation, surface fluxes)
• MOC (overflows, transports, etc)
• SSH (mean, anomaly)
• Mesoscale features (eddy ke, TIWs, Gulf Stream
  separation, Agulhas)

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CORE-III

• Protocol as for CORE-I plus freshwater flux
  anomaly of 0.1Sv around Greenland