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1 (c) 2000 Dr. David B. Stephenson Department of Meteorology University of Reading AGU Chapman conference 28 Nov – 1 Dec 2000,

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Presentation on theme: "1 (c) 2000 Dr. David B. Stephenson Department of Meteorology University of Reading AGU Chapman conference 28 Nov – 1 Dec 2000,"— Presentation transcript:

1 1 (c) 2000 D.B.Stephenson@reading.ac.uk Dr. David B. Stephenson Department of Meteorology University of Reading AGU Chapman conference 28 Nov – 1 Dec 2000, Orense, Spain The North Atlantic Oscillation

2 2 (c) 2000 D.B.Stephenson@reading.ac.uk Acknowledgements Thanks for help from the following colleagues: Pierre-Philippe Mathieu Martina Junge Martina Junge Thomas Raddatz Thomas Raddatz Abdel Hannachi Abdel Hannachi Malcolm Brooks Malcolm Brooks Kevin Hodges Kevin Hodges Note: all mistakes are my own !

3 3 (c) 2000 D.B.Stephenson@reading.ac.uk 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 ?

4 4 (c) 2000 D.B.Stephenson@reading.ac.uk 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 !

5 5 (c) 2000 D.B.Stephenson@reading.ac.uk “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 correlations World weather correlations Sir Gilbert T. Walker

6 6 (c) 2000 D.B.Stephenson@reading.ac.uk 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 …

7 7 (c) 2000 D.B.Stephenson@reading.ac.uk NAO related publications 1980-2000 All articles with “North Atlantic Oscillation” either in the title of abstact Source: web of science bibliographic database (19,213,946 documents)

8 8 (c) 2000 D.B.Stephenson@reading.ac.uk Wintertime SLP Variability Wintertime 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. 1991/921992/93 1988/891989/901990/91 1993/94 1994/95 1995/961996/97

9 9 (c) 2000 D.B.Stephenson@reading.ac.uk Positive Phase of the NAO For more details about the NAO refer to: http://www.met.rdg.ac.uk/cag/NAO +Coastal Upwelling Min. Baltic Ice Max. Baltic Inflow Small Calanus fin. stock NwAc Narrow Fast FST MAX Warm 65 Mts NAC +LSW PRODN. Storm Centre in Lab-Nordic Seas

10 10 (c) 2000 D.B.Stephenson@reading.ac.uk Negative phase of the NAO Negative phase of the NAO For more details about the NAO refer to: http://www.met.rdg.ac.uk/cag/NAO

11 11 (c) 2000 D.B.Stephenson@reading.ac.uk What is NAO ? What is NAO ? NAO + NAO - Source: Martin Visbeck and Heidi Cullen

12 12 (c) 2000 D.B.Stephenson@reading.ac.uk NAO Indices NAO Indices Gibraltar Source: Jim HURRELL

13 13 (c) 2000 D.B.Stephenson@reading.ac.uk NAO varies on all time scales …

14 14 (c) 2000 D.B.Stephenson@reading.ac.uk Power spectrum of daily NAO 1948-2000

15 15 (c) 2000 D.B.Stephenson@reading.ac.uk What makes it tick … Tropospheric processes ?Tropospheric processes ? Stratospheric processes ?Stratospheric processes ? Oceanic processes ?Oceanic processes ? Coupled processes ?Coupled processes ? Anthropogenic forcing ?Anthropogenic forcing ?

16 16 (c) 2000 D.B.Stephenson@reading.ac.uk December 1999 Storms upper level jet speed sea-level pressure low-level relative vorticity Synoptic conditions on the 23rd December 1999 showing the upper level jet speed (blue contours every 20m/s), sea-level pressure (black contours every 5mb), and low-level relative vorticity (mauve contours.) - Meteo-France

17 17 (c) 2000 D.B.Stephenson@reading.ac.uk Storm Tracks and NAO Storm Tracks and NAO Winter 1989/1990 NAO positive Winter 1995/1996 NAO negative Source: Kevin HODGES (ESSC)

18 18 (c) 2000 D.B.Stephenson@reading.ac.uk North Atlantic trends North Atlantic trends NAO related tripole in sea surface temperatures Source: Rowan Sutton Jacob Aaal Bonnevie Bjerknes 1897-1975 1897-1975

19 19 (c) 2000 D.B.Stephenson@reading.ac.uk Is it a coupled process ? Source: M.C. Escher

20 20 (c) 2000 D.B.Stephenson@reading.ac.uk Is it a coupled process ? Source: M.C. Escher

21 21 (c) 2000 D.B.Stephenson@reading.ac.uk 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  e.g. wheat qualityImpacts can lag NAO  e.g. wheat quality

22 22 (c) 2000 D.B.Stephenson@reading.ac.uk 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=1.241993 Mean=1.43 1994 Mean=0.26 1995 Mean=1.03 1996 Mean=-0.71997 Mean=0.32 Jan30 1989 Dec5 1988 Dec4 1989 Dec3 1990 Dec6 1993 Dec2 1996 Dec2 1991 Dec7 1992 Dec5 1994 Dec4 1995 Jan29 1990 Jan28 1991 Jan31 1994 Jan27 1997 Jan27 1992 Feb1 1993 Jan30 1995 Jan29 1996 Daily Values of the NAO Index

23 23 (c) 2000 D.B.Stephenson@reading.ac.uk Persistence 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) 3 1 -3 400 200 0 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

24 24 (c) 2000 D.B.Stephenson@reading.ac.uk 0 20 40 60 80 a) Autocorrelation Function Autocorrelation Function Lag 1.0 0.8 0.6 0.4 0.2 0.0 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 decorrelation time Lag in days 50 40 30 20 10 0 0 200 600 1000

25 25 (c) 2000 D.B.Stephenson@reading.ac.uk 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 Chinese philospher 604-531 B.C

26 26 (c) 2000 D.B.Stephenson@reading.ac.uk How does it affect things ? Surface conditionsSurface conditions Physical environmentPhysical environment Terrestrial ecosystemsTerrestrial ecosystems Marine ecosystemsMarine ecosystems Human activitiesHuman activities The NAO is a major factor controlling Note: the impacts are often very complex and not well understood

27 27 (c) 2000 D.B.Stephenson@reading.ac.uk Surface impacts of NAO …

28 28 (c) 2000 D.B.Stephenson@reading.ac.uk NAO and the sex life of Scandinavian ungulates

29 29 (c) 2000 D.B.Stephenson@reading.ac.uk Future events … OA26.03 Climate Variability “The Northern Oscillations: NAO and AO” European Geophysical Society XXVI General Assembly 25-30 March 2001 Nice, France Deadline for abstracts 1 Dec 2000 !!! More information: www.copernicus.org

30 30 (c) 2000 D.B.Stephenson@reading.ac.uk Consensus of specialists … Consensus of specialists …

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