Southern Annular Mode

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Southern Annular Mode
Sen Gupta and England 2006
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DOES THE OCEAN MATTER FOR THE SAM?? Autocorrelatio
n of the SAM index in model experiments
Coupled Expts
Uncoupled Expts
Sen Gupta and England 2007
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Ocean Modelling issues

• Response of the ACC to poleward intensifying
  winds increase in transport (AR4 runs) vs. eddy
  saturation (QG models)
• Response of the SO stratification to poleward
  intensifying winds coarse models (decreasing
  stratification) vs. eddying models (less change
  in stratification). important for T, ocean CO2
  change etc
• So. Why does GM not capture eddy effects wrt
  poleward wind shift expts? Is this still a
  problem at 1-deg or 0.5-deg resolution?
• Response of SO water-masses to climate change
  glacial MW and AABW freshening and warming
• Frontal locations in the ACC in IPCC AR4 models
  massive errors. Does this matter? What sets the
  front locations? Topography? Buoyancy fluxes?
  Wind stress curl?
• Mixing rates diapycnal and isopycnal
• Convection schemes and BBL flows
• GM diffusivity must be set to physically based
  values (Visbeck, Griffies scheme)
• Chronic T-S errors in water masses need for
  ocean-ice only models to separate ocean GCM
  errors from air-sea flux errors (but problematic
  as air-sea fluxes poorly constrained)
• CDW interaction with the ice-shelves
• Air-sea flux climatologies for ocean-ice only
  models
• Consistent air-sea exchange physics (momentum
  fluxes, )

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Tools

• Ocean-ice only models
• IPCC class, reanalyses, and eddying
• Coupled climate models
• Process models, theory, .
• Teams needed that bring together theory, models,
  observations, prioritising those processes that
  truly matter to IPCC projections

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Southern Ocean indices metrics

• Quantities to be used as data-based metrics for
  model evaluation
• For all models (IPCC-class through to
  eddy-resolving models)-
• 1) Drake Passage transport index, bottom
  pressure, etc., both mean and variability
• 2) Drake Passage, Hobart-AA, Greenwich meridian
  XBT repeat temperature time series
• 3) Distribution of MLD, especially in relation to
  deep winter ML's over mode water formation sites
  and stratified waters over CDW upwelling sites
• 4) Weddell and Ross Gyres e.g. Greenwich
  meridian current meter based estimates of
  transport in the Weddell gyre
• 5) T-S and tracer sections, especially CFCs,
  along WOCE lines
• 6) Sea-ice advection, sea-ice area (and possibly
  thickness?) from drifters and remote sensing
• 7) Snow thickness (from remote sensing) on
  sea-ice for freshwater fluxes
• 8) Antarctic Dipole ocean-sea-ice index
• For eddy-resolving models-
• 9) Distribution of eddy kinetic energy over the
  ACC and adjacent oceans
• 10) Location, variability and intensity of
  Southern Ocean fronts
• 11) Velocity fields in comparison with ARGO
  direct current estimates (and/or against
  assimilated dynamic height for ocean reanalysis
  products)

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Tasks for our panel wrt models

• Processes that matter for IPCC models
• Model limitations? -gt WGOMD
• Indices to inform on model skill

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Other model components

• Atmosphere
• Low-level clouds at the mid-latitudes
• Accurate simulations of the SH jet stream and its
  response to CO2/O3 change (baseline models ALL
  have peak jet stream equatorward of obs)
• Ozone hole recovery / persistence, and mechanisms
  of storm track response
• Sea-ice
• Polynyas
• Interaction with ice shelves
• Iceberg calving
• Ice shelf cavities
• Coupled issues
• Wind stress dependence on U_a vs models that have
  \tau dependent on (U_a U_o)