enso diversity in the gfdl cm2.1 coupled gcm
DESCRIPTION
ENSO diversity in the GFDL CM2.1 coupled GCM. Andrew Wittenberg NOAA/GFDL. GFDL CM2.1 global coupled GCM atmos: 2 ° x2.5 ° xL24 finite volume ocean: 1 ° x1 ° xL50 MOM4 (1/3 ° near equator) 2hr coupling; ocean color; no flux adjustments ENSO & tropics rank among top CMIP3 models - PowerPoint PPT PresentationTRANSCRIPT
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ENSO diversity in theGFDL CM2.1 coupled GCM
Andrew WittenbergNOAA/GFDL
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4000-year pre-industrial control run 1860 atmospheric composition, insolation, land cover 220yr spinup from 20th-century initial conditions big investment: 2 years on 60 processors
Delworth et al., Wittenberg et al., Merryfield et al., Joseph & Nigam (JC 2006), Wittenberg (GRL 2009)Zhang et al. (MWR 2007); van Oldenborgh et al. (OS 2005); Guilyardi (CD 2006); Reichler & Kim (BAMS 2008)
Kug et al. (JC 2010), Vecchi & Wittenberg (WIREsCC 2010), Collins et al. (Nature Geosci. 2010)
GFDL CM2.1 global coupled GCM atmos: 2°x2.5°xL24 finite volume ocean: 1°x1°xL50 MOM4 (1/3° near equator) 2hr coupling; ocean color; no flux adjustments ENSO & tropics rank among top CMIP3 models SI forecasts; parent of GFDL CMIP5 models (ESM2M, ESM2G, CM3, CM2.5)
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What sort of ENSO do we simulate?
All from asingle run with
unchanging forcings!
strong, skewed,long period,
eastward propagating(1980s & late 1990s)
weak, biennial, “Modoki”(early 1990s & 2000s)
regular &westward propagating
(1960s & 70s)
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An ENSO continuum
WP
WP
CT
CT
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Composite CM2.1 events (NDJ anomalies)
Kug et al. (JC 2010)
SST precip
heat content
(top 300m)
zonalwind
(925mb)
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CM2.1 SSTA tendency terms
Kug et al. (JC 2010)
tota
lw
mtp
uptm
hflu
x
growth via zonal & vertical
advection
poleward discharge& TC flattening
evaporation &cloud shading
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El Niño SSTA peak vs. longitude of peak
?
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less synchronization of cold events & weak warm events
strong warm events peak in SON
warm events are stronger& rarer than cold events
CM2.1 ENSO peaksvs. calendar month
abs(NINO3) > 1 stddev
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ENSO events and their nearest neighbors
strong events more
isolated
weak EN, 3yrafter strong EN
strong EN, 4yrafter weak EN
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Global equatorial SSTAs during El Niño (DJF)
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Global equatorial precip during El Niño (DJF)
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Summary
1. CM2.1 (& descendants) a fascinating resource a. Fairly realistic; wide diversity of ENSO behaviors b. Very long simulations
2. A continuum of ENSO behaviors a. Interesting extremes: WP/CT, weak/strong b. Different patterns, teleconnections, mechanisms c. Strong warm events: - SSTAs peak in east Pacific; rainfall/wind anomalies mid-basin - strong Bjerknes/thermocline feedbacks - decay via equatorial discharge d. Weak warm events: - SSTAs peak in the west Pacific; rainfall/wind anomalies confined to west - weak Bjerknes/thermocline feedbacks - decay via air-sea heat fluxes
3. Possible evidence for thresholds or “types” a. Weak warmings peak in west or east, not central Pacific b. SON upwelling might boost sufficiently strong warm events
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Reserve Slides
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20 centuries of simulated NINO3 SSTsannual means & 20yr low-pass
Wittenberg (GRL 2009)
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Long-term memory?
median6yr
10% >15yr
5-year waitmost common
recharge delay
consistentwith Poisson
But beyond 10 years?
Distribution of inter-event wait times suggests that NINO3
SSTA might have some memory beyond 5 years.
Even a purely memorylessENSO would give occasional
waits of 20 years or more,as seen in CM2.1.
Wittenberg (GRL 2009)
3822yr / 495 events= 7.7yr mean wait
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Best hope for long-term ENSO predictability?NINO3 memory might last 5yr, following strong warm events.
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Best hope for long-term ENSO predictability?NINO3 memory might last 5yr, following strong warm events.