GFDL

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GFDLs IPCC AR5 Coupled Climate Models CM2G,
CM2M, CM2.1, and CM3

• Presented by Robert Hallberg
• But the work was done by many atNOAA/GFDL
  Princeton University

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GFDLs IPCC AR5 Coupled Climate Models
CM2G CM2M CM2.1 CM3
Atmosphere AM2.1 (L24) AM2.1 (L24) AM2.1 (L24) AM3 (L48)
Land LM3 LM3 LM2 LM3
Sea ice SIS SIS SIS SIS
Ocean GOLD 1 x L63 r MOM4p1 M configuration 1 x L50 Z MOM4 1 x L50 Z MOM4p1 CM2.1-like 1 x L50 Z
New Models
ESM2G and ESM2M
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Ocean Components of GFDL Coupled Climate Models

• CM2.1/CM3 or CM2M (MOM4.0 4.1)
• 1 res. (360x200), on tripolar grid.
• 50 z- or z-coordinate vertical levels
• B-grid discretization
• Split explicit free surface fresh water fluxes
  as surface B.C.
• KPP mixed layer with 10 m resolution down to 200
  m
• Full nonlinear equation of state
• MDPPM tracer advection (CM2M)
• Tracer diffusion rotated to neutral directions
• Marginal sea exchanges specified via cross-land
  mixing
• Lee et al. Bryan-Lewis background (CM2.1) or
  Simmons et al. (CM2M) diapycnal diffusion
• Baroclinicity-dependent GM diffusivity.
• Anisotropic Laplacian viscosity (CM2.1) or
  Biharmonic Smagorinsky Resolution scaled
  Laplacian viscosity (CM2M)
• KPP specification of interior shear-Richardson
  number dependent mixing
• 2 hour baroclinic and coupling timesteps.
• Partial cell topography

• CM2G (GOLD)
• 1 res. (360x210), on tripolar grid.
• 59 Isopycnal interior layers 4 in ML
• C-grid discretization
• Split explicit free surface fresh water fluxes
  as surface B.C.
• 2-layer refined bulk mixed layer with 2 buffer
  layers
• Full nonlinear equation of state except for
  coordinate definition
• Tracer diffusion rotated to s2 surfaces
• Partially open faces allow explicit exchanges
  with marginal seas.
• Simmons et al. background diapycnal diffusion
• Visbeck variable thickness diffusivity.
• Biharmonic Smagorinsky Resolution scaled
  Laplacian viscosity.
• Jackson et al (2008) shear-Richardson number
  dependent mixing.
• 1 hour baroclinic timestep, 2 hour tracer
  coupling timesteps
• Continuously variable topography

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Pacific 2000 dbar Potential Density Surfaces from
CM2G
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100-Year Annual Mean SST Errors
CM2.1 1.17C RMS
CM2G 1.18C RMS
CM2M 1.02C RMS
CM3 1.01C RMS
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100-Year Annual Mean SSS Errors
CM2.1 0.87 PSU RMS
CM2G 0.93 PSU RMS
CM2M 1.05 PSU RMS
CM3 0.89 PSU RMS
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Broad Metrics of the Interior ocean structure
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Global Mean Temperature Bias RMS Errors, 190
Years
CM2M
CM2.1
CM2G (GOLD)
CM2G (GOLD)
CM3
CM3
CM2M
CM2.1
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RMS Temperature Errors, 0-1500 m, Years 101-200
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Temperature Anomalies at 1000 m after 190 Years
CM2G
CM2.1
CM2M
CM3
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Vertically Integrated Salinity Bias
CM2G
CM2.1
90 Yrs
190 Yrs
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Temperature Anomalies at 4000 m after 190 Years
CM2G
CM2.1
Climatology
CM2M
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Pacific and Atlantic Oceans
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Pacific Temperature Anomalies after 190 Years
CM2G
CM2.1
CM2M
CM3
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Atlantic Temperature Anomalies after 190 Years
CM2G
CM2.1
CM2M
CM3
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Atlantic Salinity Anomalies after 190 Years
CM2G
CM2.1
CM2M
CM3
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AMOC Strength in 1990 Control Runs
32 Sv
12 Sv
Year 0
Year 600
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Atlantic Salinities and Overturning Streamfunction
CM2G
CM2.1
CM2M
CM3
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Denmark Strait Topography in CM2.1 and CM2G
CM2G
CM2.1/CM2M/CM3
9 Sv
3.5 Sv

• An excessively deep Denmark Strait sill is
  ubiquitous in IPCC/AR4 models.
• In CM2G the Denmark Strait and Faroe Bank Channel
  sill depths in CM2G are set to agree with
  observed, although the channels are too wide.

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An Idealized Global warming simulation
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Changes after 110 Years in 1 per year CO2 Runs
CM2.1
CM2G
Atlantic Temperature Change Overturning
Streamfunction
SST Change
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Summary

• GFDL will be using 3 new coupled climate models
  for IPCC AR5
• (CM2G, CM2M, and CM3) plus CM2.1 from AR4.
• CM2.1, CM2M CM2G have similar time-mean SST
  biases Replacing the atmosphere in CM3 improved
  several of these.
• CM2.1, CM2M CM3 have similar interior ocean
  bias patterns, but with different magnitudes (the
  largest biases are in CM3).
• CM2G has clearly superior thermocline structure
  watermass properties, and AMOC structure, and
  very different abyssal biases.
• These differences seem to be mostly due to the
  inherent nature of the isopycnal vertical
  coordinate, compared with a geopotential
  coordinate
• Some interior ocean basin scale temperature
  biases can be directly related to surface fresh
  water forcing biases.
• Do any of these differences matter for climate
  change projections?

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Extra Slides
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Surface PropertiesSST, SSS, and Sea-ICe
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RMS Errors in Monthly SSTs
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100-Year Mean February SST Errors
CM2G
CM2.1

• RMS February SST Errors
• CM2G 1.46C
• CM2.1 1.84C
• CM2M 2.00C

Reynolds Climatology
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100-Year Mean February Depth to SST - 1C
CM2G
CM2.1
WOA2001 Climatology
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100-Year Mean Sea Surface Salinity
CM2.1
CM2G
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100-Year Mean Sea Ice Concentration
CM2G
CM2.1
March
March
September
September
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The RMS Annual-Mean SST Error
With 1990 Forcing, there is committed warming.
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Long-term Evolution of Annual Mean SST Errors
CM2G
CM2.1
Year 101-200 1.17C RMS
Year 101-200 1.18C RMS
Year 301-400 1.47C RMS
Year 361-380 1.27C RMS
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Pacific Ocean
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Pacific Ocean Temperatures, 190 Years
CM2G
CM2.1
Climatology

• Zonal Mean Pacific Ocean Potential Temperatures
• Average of Years 181-200

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Pacific Temperature Bias, 190 Years
CM2G
CM2.1
Climatology

• Possible causes of biases
• CM2.1 Excessive diffusion
• Overly entraining overflows.
• Weak abyssal flow.
• CM2G Insufficient diffusion.
• Overly wide abyssal cateracts

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Pacific Salinity Bias, 190 Years
CM2G63L
CM2.1
Climatology

• Zonal Mean Pacific Ocean Salinities
• Average of Years 181-200

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Pacific Equatorial Undercurrent in March (Equator)
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Pacific Equatorial Undercurrent in October
(Equator)
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Pacific Equatorial Undercurrent in March (140W)
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Pacific Equatorial Undercurrent in October (140W)
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ENSO Statistics for CM2G
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ENSO Spectra for CM2M and CM2G
CM2M NINO3.4 Spectrum
CM2G NINO3.4 Spectrum
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Atlantic Ocean
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Atlantic Temperature Bias, 90 Years
CM2G
CM2.1
Climatology

• Zonal Mean Atlantic Ocean Potential Temperatures
• Average of Years 81-100
• Excludes most marginal seas

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Atlantic Temperature Bias, 190 Years
CM2G
CM2.1
Climatology

• Possible causes of Atlantic bias
• Committed warming from 1990 forcing
• Circulation errors
• Excessive vertical diffusion
• Excessive exchange with Mediterranean
• Errors in NADW formation
• Salty bias from runoff precip. - evap.

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Atlantic Temperature Bias, 290 Years
CM2G
CM2.1
Climatology

• Possible causes of Atlantic bias
• Committed warming from 1990 forcing
• Circulation errors
• Excessive vertical diffusion
• Excessive exchange with Mediterranean
• Errors in NADW formation
• Salty bias from runoff precip. - evap.

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Atlantic Salinity Anomalies, 190 Years
CM2G
CM2.1
Climatology

• Zonal Mean Atlantic Ocean Salinity
• Average of Years 181-200
• Excludes most marginal seas

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Atlantic Ocean Temperatures, 190 Years
CM2G
CM2.1
Climatology

• Zonal Mean Atlantic Ocean Potential Temperatures
• Average of Years 181-200
• Excludes most marginal seas

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Atlantic Salinities, 190 Years
CM2G
CM2.1
Climatology

• Zonal Mean Atlantic Ocean Salinity
• Average of Years 181-200
• Excludes most marginal seas

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Atlantic Salinity Anomalies, 90 Years
CM2G
CM2.1
Climatology

• Zonal Mean Atlantic Ocean Salinity
• Average of Years 81-100
• Excludes most marginal seas

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Atlantic Salinity Anomalies, 290 Years
CM2G
CM2.1
Climatology

• Zonal Mean Atlantic Ocean Salinity
• Average of Years 281-300
• Excludes most marginal seas

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Vertically Integrated Salinity Errors
CM2G
CM2.1
10 Yrs
90 Yrs
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Indian Ocean
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Indian Ocean Temperatures, 190 Years
CM2G
CM2.1
Climatology

• Zonal Mean Indian Ocean Potential Temperatures
• Average of Years 181-200
• Excludes most marginal seas

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Indian Ocean Temperature Bias, 190 Years
CM2G
CM2.1
Climatology

• Zonal Mean Indian Ocean Potential Temperatures
• Average of Years 181-200
• Excludes most marginal seas

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Indian Ocean Salinities, 190 Years
CM2G
CM2.1
Climatology

• Zonal Mean Indian Ocean Salinity
• Average of Years 181-200
• Excludes most marginal seas

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Overflows Exchanges
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Resolution requirements for avoiding numerical
entrainment in descending gravity currents.

• Z-coordinate
• Require that
• AND
• to avoid numerical entrainment.
• (Winton, et al., JPO 1998)
• Many suggested solutions for Z-coordinate models
  
• "Plumbing" parameterization of downslope flow
• Beckman Döscher (JPO 1997), Campin Goose
  (Tellus 1999).
• Adding a separate, resolved, terrain-following
  boundary layer
• Gnanadesikan (1998), Killworth Edwards (JPO
  1999), Song Chao (JAOT 2000).
• Add a nested high-resolution model in key
  locations?
• Sigma-coordinate Avoiding entrainment requires
  that
• But hydrostatic consistency requires
• Isopycnal-coordinate Numerical entrainment is
  not an issue - BUT
• If resolution is inadequate, no entrainment can
  occur. Need

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Global Anomaly Patterns at fixed Depths
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Year 190 Temperature Errors at 100 m Depth

• lt 0.5 C white
• 1 C Contour interval

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Year 190 Temperature Errors at 250 m Depth

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• 1 C Contour interval

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Year 190 Temperature Errors at 600 m Depth

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• 1 C Contour interval

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Year 190 Temperature Errors at 1000 m Depth

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• 0.5 C Contour interval

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Year 190 Temperature Errors at 1500 m Depth

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• 0.5 C Contour interval

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Year 190 Temperature Errors at 2000 m Depth

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• 0.5 C Contour interval

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Year 190 Temperature Errors at 3000 m Depth

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• 0.2 C Contour interval

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Year 190 Temperature Errors at 4000 m Depth

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• 0.2 C Contour interval