volcanic source of decadal predictability in the north atlantic
DESCRIPTION
Volcanic source of decadal predictability in the North Atlantic. Didier Swingedouw, Juliette Mignot, Sonia Labetoulle , Eric Guilyardi, Gurvan Madec. DJF SST in GIN Seas ( HadISST ). A 20-yr cycle in the North Atlantic?. Swingedouw et al., in rev . - PowerPoint PPT PresentationTRANSCRIPT
Volcanic source of decadal
predictability in the North Atlantic
Didier Swingedouw, Juliette Mignot, Sonia Labetoulle, Eric Guilyardi, Gurvan Madec
DJF SST in GIN Seas (HadISST)
Swingedouw et al., in rev.
A 20-yr cycle in the North Atlantic?
Chylek et al. 2011
A 20-yr cycle in the North Atlantic?
A 20-yr cycle in the North Atlantic?
Sicre et al. 2008
Divine et al. 2006
April sea ice edge in the Nordic Seas
T,’ S’ +
EGC +
5yrs3yrs
negative delayed
feeedback
AMOC +
9yrs
10yrs
20-yr cycle in IPSLCM5
2yrs
convection +
Sea ice cover -,
SLP-
Escudier et al., in rev.
Advection as in Great Salinity Anomalies
How can we intialize this 20-
yr cycle in the model?
Experimental design
5-member historical ensemble with natural and antrhopogenic radiatiuve forcing
5-member initialised ensemble nudged with SST anomalies (Reynolds et al. 2007) superimposed on each historical simulation over the period 1949-2005:
3-member hindcast ensemble every 5 years (with white noise on SST) and forecast or projection ensemble
3-member ensemble with only natural and anthropogenic forcing
AgungEl Chichon
Pinatubo
AMOC Initialisatio
n Reconstructions of the
AMOC using NODC hydrographic data (Huck et al. 2008) and Latif et al. (2003)
Agreement between nudged and reconstructions
Synchronisation also in the historical simulations
Obs. (Huck et
Historical
Reconstruction
Nudged
Control
CV sites response
Convection sites explain AMOC variations
Mechanisms
Agung eruption 1963-1966
GIN SST and sea-ice cover Wind stress & EGC SSS Labrador Sea CV sites AMOC Phasing of the second
maximum• Labrador Sea SSS = 7-10 years
predictor of the AMOC• EGC = more than 10 years
predictor
GSA GSA GSA
T,’ S’ +
EGC +
5yrs3yrs
negative delayed
feeedback
AMOC +
9yrs
10yrs
Initialisation du cycle à 20 ans
2yrs
convection +
Sea ice cover -,
SLP-
Escudier et al. In rev.
Agung eruption
Attribution simulations
Agung eruption in 1963 resets the 20-yr cycle in natural simulations as in historical ones, not the case in anthropogenic ones
Impact of volcanic forcingClimatic index
Time
Model free
Agung
15 yrs
1963 1982 1991 2006
Impact of volcanic forcingClimatic index
Time
Agung
15 yrs
El Chichon
1963 1982 1991 2006
Impact of volcanic forcing
Time
Agung
15 yrs
El Chichon
Pinatubo
1963 1982 1991 2006
Destructive interference
Kanzow et al. 2010
Climatic index
Impact of volcanic forcing
Need of simulations without
Pinatubo to confirm this
idea
A simple physical model
The purple curve is a simple model of the 20-yr response to the 3 major volcanoes plus a weakening due to anthropogenic forcing:
Conclusions
A 20-yr favored frequency in the North Atlantic in IPSL-CM5: agreement with a few data
Simple initialisation technique succeeds in synchronizing the AMOC
Due to volcanic triggering of the 20-yr cycle And the effect of the NAO in the 1980s and 1990s Effect of Pinatubo: destructive interference?
HindcastsAMOC 48°N
Only one member of the nudged ensemble (planned to apply to each)
3-member ensemble of free run
Good predictive skill for the AMOC in perfect model analysis (Persechino et al., sub.)
90’s max. missed
HindcastsAMOC 48°N
Only one member of the nudged ensemble (planned to apply to each)
3-member ensemble of free run
Good predictive skill for the AMOC in perfect model analysis (Persechino et al., sub.)
90’s max. missed
Hindcasts
Another ensemble
CV sites response in projections
Escudier et al. mechanism in
projections
Discussion Iwi et al.
Discussion Iwi et al.
Propagation of SST anomalies We follow the
mininimum of SST along the gyre
7 years between Labrador and GIN
True in the model (known)
And in the SST Reynolds data!
Box 1
Box 2
Box 3
Box 4
GSA GSAGSA
Air-sea ice interactions
Anomalous wind stress in the NCEP and HadISST sea ice, similar to what is obtained in the simulations.
An indication of the existence of the air-sea-sea ice interaction from our 20-yr cycle.
NCEP & HadISST
Nudgedensemble
Historicalensemble
% sea ice cover
Hindcasts
What do we expect from initialisation?Climatic index
Time
Observations
Model free Model
initialised
Assumptions:1. Climatic oscillations correctly represented in model (frequency,
amplitude)?2. There exists ways to phase the two signals using coupled
models?