ENSO Prediction and Interactive Ensemble Using CCSM3€¦ · ENSO Prediction and Interactive...
Transcript of ENSO Prediction and Interactive Ensemble Using CCSM3€¦ · ENSO Prediction and Interactive...
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ENSO Prediction andInteractive Ensemble Using
CCSM3
Edwin K SchneiderGeorge Mason University and COLA
Ben P. KirtmanGeorge Mason University and COLA
Dughong MinCOLA
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Two COLA Projects UsingCCSM3
• ENSO prediction using CCSM3.0– Description– Results of retrospective forecast
ensembles• Interactive ensemble version of
CCSM3.0 using flux coupler– Description– Preliminary results
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History of ENSO ForecastExperiment with CCSM
• Tribbia– (1982-83) event case studies using various
version of CCM• Schneider, DeWitt, Rosati, Kirtman, Ji, and
Tribbia (MWR, 2003)– CCM3 (CAM1) coupled to MOM3 retrospective
forecasts• Kirtman and Min (2007)
– These results– First set of retrospective forecasts using an official
version of CCSM (including flux coupler)
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Technical Details• Model
– CCSM3.0 T85• Initial Conditions (1982-1998)
– Ocean: provided by GFDL (Rosati) andinterpolated to CCSM3 ocean grid
– Atmosphere: from archived 20th century SSTforced simulation
• 6 member ensembles for Jan. 1 and Jul. 1initial conditions 1982-1998– Ensemble members from perturbed atmospheric
initial conditions
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Results
• 6 case ensembles CCSM3• 15 case ensembles CFS (T62L64)
CCSM equatorial cold bias, double ITCZ,semiannual annual cycle, biennial ENSO
CFS little equatorial cold bias, realistic ENSOperiod
• Comparison and ensembling of the twosets of forecasts (mean bias removed)
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CCSM3.0 Jan 1982 IC CFS Jan 1982 IC
Can see systematic error in ENSOevolution
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CCSM3.0 Jan 1983 IC CFS Jan 1983 IC
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CCSM3.0 Jan 1988 IC CFS Jan 1988 IC
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Comparison
• Systematic errors in ENSO fromcoupled simulations carry over topredictions
• CFS hangs on to warm events too long• CCSM does a good job on predicting
cold events
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Please see poster byMin and Kirtman for
more details
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Interactive EnsembleVersion of CCSM3
• A new tool being developed for the CCSMcommunity
• Couple ensemble mean of AGCMs (CAM3) tothe other components through the fluxcoupler– Each AGCM started from different initial conditions,
so weather noise uncorrelated– Ensemble mean filters out weather noise (variance
1/N for N atmospheres)– Reduces variability forced by weather noise but
leaves unstable coupled variability (if there is any)– Response to specified forcing will be deterministic
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Interactive Ensemble CGCM(in COLA CGCM)
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Interactive Ensemble CCSM3
AGCM1 AGCM2 AGCMn…
Flux Coupler
(modified)
OGCM
Land Sea Ice
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Configuration
• 6 copies of CAM3• Embarrassingly parallel (wall clock ~
that for CCSM3)
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Conclusions
• CCSM3 has been tested for seasonal-to-interannual prediction and should bea useful tool.
• An interactive ensemble version ofCCSM3 has been constructed and isbeing tested.