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![Page 1: Importance of physics in global hindcast simulations of ... · PDF fileImportance of physics in global hindcast simulations of sea ice with NEMO-LIM François Massonnet, T. Fichefet,](https://reader033.vdocuments.mx/reader033/viewer/2022042708/5a78e4d87f8b9ae6228e9444/html5/thumbnails/1.jpg)
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T.G.I.F.
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Importance of physics in global hindcastsimulations of sea ice with NEMO-LIM
François Massonnet, T. Fichefet, H. Goosse, M. Vancoppenolle, P. Mathiot, C. König Beatty
[email protected] www.climate.be/u/fmasson
Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute,Université catholique de Louvain
EGU General Assembly 03-08 April 2011
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Inter-GCMs spread and simulated polar climate
Modeled minus observed mean monthly sea ice extents (1979-2004) from 11 major General Circulation Models.(Fig. 4 of Parkinson et al. (2006) )
• Spread possibly due to differences in resolution, atmosphericcomponent, sea ice component
• IPCC AR4: no outstanding model (Arzel et al., 2006)
How to evaluate a sea ice model? How does the representation of its physics component matter?
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Outline
2 experiments differing only in their sea ice components1
Evaluate outputs from bothexperiments with suitable metrics
2
Discuss physical processes possiblyresponsible for differences
3
EXP1 EXP2
Experimental setup
Models evaluation
Discussion
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1. Experimental setup
NCEP/NCAR daily surface temperatures and windsMonthly climatologies of relative humidity, cloud cover, precipitations and river runoff
NEMO 3.1Madec, 2008
• Primitive equation free surface OGCM• Level-1.5 turbulence closure scheme• Isopycnal mixing + G&M param. of eddy-inducedtracer advection• 42 vertical levels• Salinity restoring
LIM2Fichefet and Morales
Maqueda, 1997
• Simple ice thickness dist.• 2+1 layers ice and snow• Basic brine modelling
• VP rheology• B-grid
LIM3Vancoppenolle et al., 2009
• 5 ice categories• 5+1 layers ice and snow• Explicit brine, salinitydistribution• EVP rheology• C-grid
2 sea ice modelsOcean model
www.climate.be/lim www.nemo-ocean.eu
~ 1° resolution (climatic-like)1948-2007 simulationFocus on 1983-2007
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2. Models evaluation
Monthly mean seasonal cycle of sea ice extent (1983-2007)
Metric ≡ abs(model – obs)
typical error
metric10
« best »model
« good »model
« bad »model
NorthernHemisphere (NH)LIM2: 1.33LIM3: 0.43
SouthernHemisphere (SH)LIM2: 3.58LIM3: 1.17
(the lower, the better)
OBS: OSISAF, 2010
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2. Models evaluation
Metrics std anomalies:LIM2: 0.48 LIM3: 1.10
Monthly anomalies of sea ice extent (NH)
Metrics std anomalies:LIM2: 1.22 LIM3: 0.61
Monthly anomalies of sea ice extent (SH)
(the lower, the better)
(the lower, the better)
Sept. 2007 Sept. 2007
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2. Models evaluationModel minus obs difference in sea ice draft/thickness [m]
Metrics
LIM2: 0.94 LIM3: 0.67
Obs: ASPecT (Worby et al., 2008)
Obs: ULS (Rothrock et al., 2008)
MetricsLIM2: 3.22 LIM3: 2.45
(the lower, the better)
(the lower, the better)
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3. Discussion (NH)
LIM2 LIM3
Conc.
Extent
Thick.
Drift
Framexport
MeanStd of anomaliesTrend
MeanStd of anomaliesTrend
MeanTrend
Mean kinetic energyCirculation pattern
Mean areaStd anomalies areaMean volumeStd anomalies volume
Metrics
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3. Discussion (NH)
LIM2 LIM3
Conc.
Extent
Thick.
Drift
Framexport
• Ice thickness distribution: Metrics confirm earlier resultsof Bitz et al. (2001) and Holland et al. (2006) with GCMs.• Importance of salinity variations in LIM3 (Vancoppenolle et al., 2009)
• Models parameters not tuned for optimizing drift • LIM2 (VP) versus LIM3 (EVP); EVP more responsive to wind forcing (Hunke and Dukowicz, 1997)
mean ice
thickness
LIM2
LIM3
Metrics
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3. Discussion (SH)
Conc.
Extent
Thick.
Drift
LIM2 LIM3
MeanStd of anomaliesTrend
MeanStd of anomaliesTrend
Mean
Mean kinetic energyCirculation pattern
Metrics
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3. Discussion (SH)
Conc.
Extent
Thick.
Drift
LIM2 LIM3
• No outstanding model!
• SH is different from NH in many respects:
o Dynamics of the Southern Ocean and unresolvedsmall-scale processes (Rintoul et al., 2001)
o Quality of the reanalyses (Vancoppenolle et al., 2010; Vihma et al., 2002; Timmerman et al., 2004)
o Thinner ice than NH
Metrics
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T.G.I.F. - Take home message
2 hindcast (1983-2007) experiments with the OGCM NEMO-LIM at climatic resolution, differing only in their sea ice component
Set of comprehensive metrics evaluating main seaice variables, for both hemispheres
+• Skill is model-dependent in NH
• Limitations of skill in SH are not due to model physics
Conclusions could be sensitive to experimental setup
[email protected] www.climate.be/u/fmasson