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(c) 2000 [email protected]
Dr. David B. Stephenson
Department of Meteorology
University of Reading
AGU Chapman conference 28 Nov – 1 Dec 2000, Orense, Spain
The North Atlantic OscillationThe North Atlantic Oscillation
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(c) 2000 [email protected]
AcknowledgementsAcknowledgements
Thanks for help from the following colleagues:
• Pierre-Philippe MathieuPierre-Philippe Mathieu• Martina JungeMartina Junge• Thomas RaddatzThomas Raddatz• Abdel HannachiAbdel Hannachi• Malcolm BrooksMalcolm Brooks• Kevin HodgesKevin Hodges
Note: all mistakes are my own !
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(c) 2000 [email protected]
Some important NAO questions …Some important NAO questions …
• What exactly is it ?What exactly is it ?
• What makes it tick ?What makes it tick ?
• How well can it be forecast ?How well can it be forecast ?
• How does it affect things ?How does it affect things ?
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What should we call it ?What should we call it ?
• Druck SchwankungenDruck Schwankungen• Northern OscillationNorthern Oscillation• North Atlantic OscillationNorth Atlantic Oscillation• Arctic OscillationArctic Oscillation• Annular modeAnnular mode• Not the Arctic OscillationNot the Arctic Oscillation• Al MoubarakAl Moubarak• El NaoEl Nao• Le YoYo MeteoLe YoYo Meteo• Northern Wazaaaaaa ! Northern Wazaaaaaa !
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“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.” (1908)
World weather correlationsWorld weather correlationsSir Gilbert T. WalkerSir Gilbert T. Walker
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Early history of NAO research …Early history of NAO research …
• Saabye 1770-8Saabye 1770-8• Teisserence de Bort 1883Teisserence de Bort 1883• Hann 1890Hann 1890• Hildebrandsson 1897Hildebrandsson 1897• Meinardus 1898Meinardus 1898• Pettersson 1905Pettersson 1905• Exner 19??Exner 19??• Walker 1908, 1924, 1932Walker 1908, 1924, 1932• Defant 1924Defant 1924• Loewe 1937Loewe 1937• Van Loon and Rogers 1978Van Loon and Rogers 1978• + many others …+ many others …
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NAO related publicationsNAO related publications1980-20001980-2000
0
20
40
60
80
100
120
1981 1984 1987 1990 1993 1996 1999
Articles
All articles with “North Atlantic Oscillation” either in the title of abstactSource: web of science bibliographic database (19,213,946 documents)
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Wintertime SLP VariabilityWintertime SLP Variability SLP Anomalies Dec/Jan/Feb (1988-1997)
Anomalies in wintertime mean sea-level pressure (contours every 2mb).
Note the recurrent NAO dipole pattern in the Atlantic sector.
1991/92 1992/93
1988/89 1989/90 1990/91
1993/94
1994/95 1995/96 1996/97
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Positive Phase of the NAOPositive Phase of the NAO
For more details about the NAO refer to: http://www.met.rdg.ac.uk/cag/NAO
+CoastalUpwelling
Min. Baltic IceMax. BalticInflow
SmallCalanus fin.
stock
NwAc Narrow Fast
FSTMAX
Warm
65 Mts NAC
+LSWPRODN.
Storm Centre inLab-Nordic Seas
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Negative phase of the NAONegative phase of the NAO
For more details about the NAO refer to: http://www.met.rdg.ac.uk/cag/NAO
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What is NAO ?What is NAO ? NAO + NAO -
Source: Martin Visbeck and Heidi Cullen
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Power spectrum of daily NAO 1948-2000Power spectrum of daily NAO 1948-2000
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What makes it tick …What makes it tick …
• Tropospheric processes ?Tropospheric processes ?
• Stratospheric processes ?Stratospheric processes ?
• Oceanic processes ?Oceanic processes ?
• Coupled processes ?Coupled processes ?
• Anthropogenic forcing ?Anthropogenic forcing ?
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North Atlantic trendsNorth Atlantic trends
NAO related tripole in sea surface temperatures
Source: Rowan Sutton
Jacob Aaal Bonnevie BjerknesJacob Aaal Bonnevie Bjerknes 1897-19751897-1975
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Is it a coupled process ?Is it a coupled process ?
Source: M.C. Escher
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Is it a coupled process ?Is it a coupled process ?
Source: M.C. Escher
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How well can we forecast it ?How well can we forecast it ?
NAO = some trends + a lot of noise
X(t) f(t) e(t)
• Persistent trend part f(t) gives some skill. Persistent trend part f(t) gives some skill. • Amount of skill depends on the lead time !Amount of skill depends on the lead time !• Even low skill may be very useful !Even low skill may be very useful !• Impacts can lag NAO Impacts can lag NAO e.g. wheat quality e.g. wheat quality
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Daily values of the NAO index obtained by projecting daily sea-level pressure onto the NAO pattern. - In collaboration with T. Strunk.
1989 Mean=1.78 1990 Mean=1.02 1991 Mean=0.67
1992 Mean=1.24 1993 Mean=1.43 1994 Mean=0.26
1995 Mean=1.03 1996 Mean=-0.7 1997 Mean=0.32
Jan301989
Dec51988
Dec41989
Dec31990
Dec61993
Dec21996
Dec21991
Dec71992
Dec51994
Dec41995
Jan291990
Jan281991
Jan311994
Jan271997
Jan271992
Feb11993
Jan301995
Jan291996
Daily Values of the NAO IndexDaily Values of the NAO Index
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Persistence in the NAO Time SeriesPersistence in the NAO Time Series
Note the persistence in a) and the slow predictable movement in b).
a) Daily NAO index (1 Jan. 1989 to 30 Dec. 1997)
b) Accumulated Daily NAO index (1 Jan. 1989 to 30 Dec. 1997)
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1
-1
-3
400
200
0
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
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0 20 40 60 80
a) Autocorrelation Function
Aut
ocor
rela
tion
Fun
ctio
n
Lag
1.0
0.8
0.6
0.4
0.2
0.0
Persistence in daily NAO …Persistence in daily NAO …
Autocorrelations persist up until very long lags => early warning system may be possible (few week's lead).
b) Decorrelation Time vs Maximum Lag
deco
rrel
atio
n tim
e
Lag in days
50
40
30
20
10
00 200 600 1000
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Some wise words …Some wise words …“Those who have knowledge, do not predict,Those who have knowledge, do not predict,
Those who predict, do not have knowledge.” Those who predict, do not have knowledge.” - Lao Tzu Lao Tzu
Chinese philospher 604-531 B.CChinese philospher 604-531 B.C
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How does it affect things ?How does it affect things ?
• Surface conditionsSurface conditions
• Physical environmentPhysical environment
• Terrestrial ecosystems Terrestrial ecosystems
• Marine ecosystemsMarine ecosystems
• Human activitiesHuman activities
The NAO is a major factor controllingThe NAO is a major factor controlling
Note: the impacts are often very complex and not well understood
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NAO and the sex life of Scandinavian ungulatesNAO and the sex life of Scandinavian ungulates
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Future events …Future events …
OA26.03 Climate VariabilityOA26.03 Climate Variability““The Northern Oscillations: NAO and AO”The Northern Oscillations: NAO and AO”
European Geophysical SocietyEuropean Geophysical SocietyXXVI General AssemblyXXVI General Assembly25-30 March 2001 Nice, France25-30 March 2001 Nice, France
Deadline for abstracts 1 Dec 2000 !!!Deadline for abstracts 1 Dec 2000 !!!More information: www.copernicus.orgMore information: www.copernicus.org