1. Climate teleconnections in the Euro-Atlantic region
Dr. David B. Stephenson
Department of Meteorology
University of Reading
Overview of Euro-Atlantic teleconnection patterns
An example: European rainfall in Autumn 2000
North Atlantic ocean effects
(c) 2002

2. (c) D.B.Stephenson@reading.ac.uk 2002
Sir Gilbert Walker
Correlations with pressure
“The relationships between weather over the Earth are so complex that it seems useless to try to derive them from theoretical considerations; and the only hope at present is that of ascertaining the facts and of arranging them in such a way that interpretation shall be possible.”
Correlations with temp
(c) 2002
Dr. David Stephenson

3. Positive Phase of the NAO
+CoaalUpwelling
Min. Baltic
Ice
Max. Baltic
Inflow
Small
Calanus fin.
stoc
NwAc Narrow Fast
FST
MAX
Warm
65 Mts NAC
+LSW
PRODN.
Storm Centre in
Lab-Nordic Seas
Highly idealised schematic of NAO positive phase
In reality, no individual year looks like this – but variations on it.
For more details about the NAO refer to:
(c) 2002
Dr. David Stephenson

4. Winter NAO index: 1864-2001 Gibraltar
© David B. Stephenson
(c) 2002
Image source: Jim HURRELL
Dr. David Stephenson

5. Global correlations with the NAO index
SLP
Temperature
Precipitation
Zonal wind
(c) 2002

6. Anders Knut Ångström’s word “Teleconnection”
A. Ångström (1935) Teleconnections of climatic changes in present time, Geogr. Annal., 17,
“the weather at a given place is not an isolated phenomenon but is intimately connected with the weather at adjacent places”
Chief causes of teleconnections:
I. Local extension of a given feature
II. Propagation of weather systems
III. Existence of changes of great extension that affects local weather: 1. Energy reaching the Earth
2. Atmospheric circulation
3. Other
(c) 2002

7. (c) D.B.Stephenson@reading.ac.uk 2002
Empirical Orthogonal Function analysis
Grid point variables  Principal Components
PCs ranked in order of how much variance they explain
Allows dimension reduction
Known as Principal Component Analysis (PCA) in statistics
(c) 2002

8. (c) D.B.Stephenson@reading.ac.uk 2002
Northern Hemisphere wintertime teleconnection patterns
NAO
PEU
EU-1
PNA
EAO
EA/WR
EPJ
TNH
WPJ
Leading rotated
EOFs of 700mb
geopotential
Height
Source:
Gerry Bell, CPC
(c) 2002

9. (c) D.B.Stephenson@reading.ac.uk 2002
Euro-Atlantic wintertime teleconnection patterns
(c) 2002

10. (c) D.B.Stephenson@reading.ac.uk 2002
Euroatlantic winter (DJF mean) reconstructed CPC indices
CPC indices
reconstructed
from historical European
temperature
and pressure measurements
Source: J. Luterbacher
(c) 2002

11. (c) D.B.Stephenson@reading.ac.uk 2002
Autumn 2000 rainfall (Sep-Nov) percent of long-term mean
England Wales Precipitation (EWP) is the average of rainfall over the 5 UK regions south of Scotland. It is obtained by taking the weighted average of about 60 rain gauges.
Wigley et al. 1984
Wigley and Jones 1986
Gregory et al. 1991
Jones and Conway 1996
Osborn et al. 2000
Alexander and Jones 2000
(c) 2002

12. Autumn (Sep-Nov) totals of England Wales Precipitation 1766-2001
Centered about
mean of 271mm
2001
event
(c) 2002

13. A “wake-up call” for climate change
“Extremes will become the norm”
John Prescott,
Deputy Prime Minister
November 2000
(c) 2002

14. (c) D.B.Stephenson@reading.ac.uk 2002
500hPa streamfunction anomaly Sep-Nov 2000
Note the wave-train
pattern extending
from the Atlantic
over NW Europe with
a high over Scandinavia
and a low over the UK.
Source: Mike Blackburn
(c) 2002

15. Daily Euro-Atlantic teleconnection indices 1 Sep – 31 Dec 2000
Note the 3 month
persistence in the
Scandinavian index
(c) 2002

16. Scatter plot of Autumn EWP totals versus reconstructed EU1 index
r=0.36
(c) 2002

17. (c) D.B.Stephenson@reading.ac.uk 2002
DJF
MAM
Correlation maps
of global SLP with
EWP seasonal totals
SON
JJA
© Matt Sapiano
(c) 2002

18. (c) D.B.Stephenson@reading.ac.uk 2002
Source: Matt Sapiano’s ongoing PhD thesis work at Reading
(c) 2002

19. Jacob Bjerknes’s N. Atlantic studies
1959: The recent warming of the
North Atlantic, Rossby Mem. Vol.
1960: Ocean temperatures and
atmospheric circulation, WMO Bull.
1961: Climatic change as an
ocean-atmosphere problem,
Proc. of Rome Symposium.
1962: Synoptic survey of the
interaction of sea and atmosphere
in the North Atlantic, G. Norvegica
1964: Atlantic air-sea interaction,
Advances in Geophysics, vol. 10.
Jacob Aaal Bonnevie Bjerknes
(c) 2002
Dr. David Stephenson

20. (c) D.B.Stephenson@reading.ac.uk 2002
Variations of N. Atlantic SSTs and NAO SLP index
J. Bjerknes, Geophysica Norvegica, 24, No. 3, 1962.
(c) 2002

21. (c) D.B.Stephenson@reading.ac.uk 2002
J. Bjerknes’s long-term changes in SLP and SST
Lat
r(NAO,T)
61.5N
-0.34
57.5N
-0.82
52.5N
47.5N
0.18
42.5N
0.33
37.5N
-0.37
(c) 2002

22. (c) D.B.Stephenson@reading.ac.uk 2002
J. Bjerknes’s short term variations in SLP and SST
(c) 2002

23. (c) D.B.Stephenson@reading.ac.uk 2002
How much direct role do North Atlantic SSTs have
in determining NW Europe temperature variations?
NAO
SST tripole ? ?
DJF central england temperature anomalies
M. Junge and D.B. Stephenson (2002) "Mediated and direct effects of the
North Atlantic ocean on winter temperatures in northwest Europe“,
Int. Journal of Climatology (submitted).
(c) 2002

24. (c) D.B.Stephenson@reading.ac.uk 2002
MUTUAL CORRELATIONS
NAO
Central England
Temperature
r=0.67
r=-0.38
r=-0.30
SST tripole
(c) 2002

25. The linear modelling approach
To unravel the indirect from the direct effects
we need to go beyond decriptive methods
(correlation analysis) and introduce a model:
Using data from , we obtain estimates of:
The fit explains 45% of the total CET variance and
is statistically significant at p<0.001
(c) 2002

26. (c) D.B.Stephenson@reading.ac.uk 2002
Direct and indirect effects
NAO
Central England
Temperature
a=0.64
r=-0.38
b-=-0.06
SST tripole
r(CET,NAO)=0.67=0.64+(-0.38)x(-0.06)
r(CET,SST)=-0.30=-0.06+(-0.38)x(0.64)
So most of correlation between SST and
CET is coming indirectly via the NAO’s
influence on both variables.
(c) 2002

27. The best explanatory fields for NW Europe temperatures
SLP
NAO-like SLP pattern
shifted eastwards
explains 63% of variance
SST
Direct effect not the SST tripole
Strong near Newfoundland
Ratcliffe and Murray (1970)
explains 5% of CET variance
(c) 2002

28. (c) D.B.Stephenson@reading.ac.uk 2002
Main Conclusions
5 main teleconnections for Europe in winter: PEU,NAO,EAO, SCA,EAWR,PNA
Teleconnections are of use for understanding climate events e.g. Autumn 2000
The correlation between North Atlantic SSTs and European climate is mainly an indirect effect mediated by the ocean’s response to the atmospheric flow.
(c) 2002