CMIP5 decadal experiments at CERFACS: Initialisation and preliminary results Aspen CMIP5 workshop,Colorado, June 2011 Christophe Cassou, Emilia Sanchez-Gomez Elodie Fernandez Laurent Terray
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CMIP5 decadal experiments at CERFACS: Initialisation and preliminary results
Aspen CMIP5 workshop,Colorado, June 2011
Christophe Cassou, Emilia Sanchez-Gomez Elodie Fernandez Laurent Terray
Prediction or forecast?
Predic'on = prédic'on Forecast = prévision
Meteorologist, climatologist Miss Sun, astrologist
Outline
OUTLINE
1. Descrip'on of the CERFACS model and CERFACS contribu'on to CMIP5 database
2. Impact of the ini'alisa'on technique upon model ini'al shock and driL
3. Very preliminary results about AMO predictability
The Cerfacs-CNRM contribution to the CMIP5 database
All simulations are completed and model outputs have been posted last week end on ESG nodes (except sea-ice data)
Core experiments
« Tier 1 »: 1. Increase ensemble sizes from 3 to 10 members
2. Forecast with 2010 Pinatubo eruptions (10 members)
3. Work on initialization techniques
« Bonus »: 10 more dates starting one year before the requested CMIP5 experiments
The decadal forecast initialization
The coupled model = CNRM-CM5
Land surface, ISBA
SURFEX Interface
Atmosphere ARPEGE-Climat v5.2
T127 (1.4°), 31 levels
Ocean NEMO v3.2 1°
42 levels
River Routing TRIP
Sea Ice GELATO v5
OASIS v3 (24h coupling)
24h
The COMBINE ECMWF Ocean Reanalysis
Full Initialization: Ocean Only In a coupled mode from 1958
To 2008
3D Nudging as a function of depth and space
β = f(depth, space) Reanalysis
Current
No 3D nudging within the
Equatorial band (1oN-1oS) and near the coast
(300km) (1/ β) =0
In the mixed layer (1/ β) =0
Deep Ocean β = 360 days
Below thermocline β = 10 days
Sea surface restoring
Heat flux:
Heat flux at the surface
feedback term. SSTobs= observations
Feedback coefficient = -40W/m2/K
Fresh water flux:
Fresh water budget at the surface
Feedback term. SSSobs= observations
Feedback parameter = -167 mm/day
At the surface
Outline
Sensi'vity of the ini'al shock and driL to the 3D‐nudging domain of applica'on
Two types of CMIP5 experiments
GLOB No 3D nudging within the 1°S–1°N band
• Nudging to the ECMWF ocean reanalysis NEMOVAR (ORCA1°) 1958 -2008 • Several tests have been performed to set the optimal parameters for dQ/Dt and β
EXTROP No 3D nudging Within the 15°S–15°N band
Ocean Heat Content
Mean 1960-2005
ΔH EXTROP GLOB
NEMOVAR
Mean 1960-2005
Along the equatorial thermocline
(GLOB-EXTROP) (HIST-NEMOVAR) Mean [1960-2005] Temperature difference averaged over the 2oN-2oS band
Impact of initialization on mean ocean heat transport
GLOB: perturbation of the Northward heat transport around 10o Of latitude
GLOB: perturbation of the Northward heat transport around 10o Of latitude in the Atlantic
EXTROP: close to HIST up to 20oN close to NEMOVAR northward
Impact of initialization on prediction
Global Mean SST
GLOB / EXTROP
Strong warm initial shock mainly due to very rapid austral ocean warming
Annual mean SST biases (HIST-ERSST (1960-2005)
6 months
2-3 years
> 10 years
Impact of the initialization on predictions
Global Mean SST (from 35oS to 90oN)
1-yr warming much drift less pronounced
GLOB warm shock stronger than EXTROP
GLOB / EXTROP
Thermocline depth prediction
3-member ensemble Mean D20 isotherm depth over the 2oN-2oS band 1 spaghetti = 1 forecast date
GLOB/EXTROP
HIST
ENSO variability
NINO34 SST
Ensemble mean (dates+members) Nino34 SST index
Yr1 Yr2 Yr3 Yr4
Perturbation of the tropical climate up to 4yr (systematic NINO the 1st and 3rd year in GLOB)
Teleconnection
Difference between GLOB and EXTROP ensemble mean (dates+members) Z500 and precipitation for the 1yr-forecast winter
Strong difference in rainfall drift between GLOB and EXTROP, presence of ENSO Teleconnection in Z500 drift
Color=precip / contour=Z500 (significance hatching)
Does the drift affect skills?
2 questions:
1. Do the strength and physical structures of the initial shock and subsequent drift affect the skill of the forecast at decadal time-scale (yr 2-5?)
2. What is the relevance of linear debiasing methods in presence of drifts that DO project on natural modes of variability that are clearly nonlinear (convection and teleconnection associated with ENSO)?
Outline
Preliminary results on model skill and AMO predictability
26 June ‐1 July 2011 CMIP5 Decadal Predic8on Workshop, Aspen
SST Correlation skill (with trend)
Decadal Forecast
Historical 20th simulations
26 June ‐1 July 2011 CMIP5 Decadal Predic8on Workshop, Aspen
SST Correlation skill (without trend)
Decadal Forecast
Historical 20th simulations
26 June ‐1 July 2011 CMIP5 Decadal Predic8on Workshop, Aspen
Global (60°S-60°N) SST Predictability
OBS=ERSST3 DEC HIST
26 June ‐1 July 2011 CMIP5 Decadal Predic8on Workshop, Aspen
Detrended global (60°S-60°N) SST
OBS=ERSST3 DEC HIST
26 June ‐1 July 2011 CMIP5 Decadal Predic8on Workshop, Aspen
AMO Predictability
OBS=ERSST3 DEC HIST
Conclusions
• We need to be extremely cautious in the way ocean 3D fields are initialized
• Model drift correction is a central question (interaction with the forcing and the natural variability modes)
We need to be very cautious with the estimation of the decadal forecast skill (choice of the statistics etc.) and with the way users are going to deal with the decadal forecasts
The Cerfacs-CNRM data are available! Feel free to use them!
IPO/PDO ERSST3 1890-2010
IPO/PDO Predictability
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