Non-Stationarity in the circulation-climate relationship Stability of NAO-Influence on the Regional...

Non-Stationarity in the circulation-climate relationship

Stability of NAO-Influence on the Regional Climate of the Baltic Sea Area

Possible Effects on NAO-Reconstructions?

(1) GKSS Research Center Geesthacht – Institute for Coastal Research – System Analysis and Modeling(2) Göteborg University – Earth Sciences Center – Ocean Climate Group

(1) Frederik Schenk, Sebastian Wagner, Eduardo Zorita(1) Frederik Schenk, Sebastian Wagner, Eduardo Zorita

(2) Daniel Hansson(2) Daniel Hansson

Outline

1 Non-Stationarity in Observations1 Non-Stationarity in Observations

- spatiotemporal changes of NAO-control on regional climate

2 Non-Stationarity in Climate Model Simulations2 Non-Stationarity in Climate Model Simulations

- temporal evolution of the NAO-t2m-relationship over 990 years

3 Idealized pseudo-proxy reconstruction of NAO from local-scale3 Idealized pseudo-proxy reconstruction of NAO from local-scale

4 Summary4 Summary

Assumption of Stationarity in Climate Reconstructions

Most statistical reconstructions assume stationarity between climate circulation and regional climate impact (proxy location)

i.e. linear relationship between NAO and near-surface climate

n

kkkBaltic ttpctT

1

)()()(

Local climate = F(large-scale + x)

Regional climate orlocal proxy

Proportionalconstant

Large scalei.g. PC

Residuum notcaptured by

linear equation

physical assumption:

First leading EOFs of 1000-1990

PCA calculates covariability matrix of SLP field anomalies

1 Non-Stationarity in observations

The NAO – temperature relationshipThe NAO – temperature relationship

Definition of circulation indices and T-Baltic from Echo-G and Luterbacher-SLP-reconstruction

http://www.baltex-research.eu/BACC/media/

Detection of Non-Stationarity

Non-StationarityNon-Stationarity

=: changes in strength of a relationship between two climate variables

- expressed as Running Correlation coefficients over time (Pearson)

- window size of 31 years = RC30

Data

Surface Temperature (t2m)Surface Temperature (t2m)

Long historical station temperatures

T-Baltic (t2m) of different AOGCM simulations from ECHO-G

MIB (MIB (MMax. sea-ax. sea-IIce extent of the ce extent of the BBaltic Sea)altic Sea)

MIB (obs.) (Seinä & Palosuo 1996)

MIB (mod.) – box-model PROBE-Baltic (Hansson & Omstedt 2007)

Circulation indicesCirculation indices

NAO of Azores minus Iceland (Jones et al. 1997)

NAO from 500 year SLP-reconstruction (Luterbacher et al. 2002)

NAO from SLP of different simulations from ECHO-G

with different forcings and initial conditions

Time evolution of NAO-temperature relation

64%

9%


NAO and sea-ice (MIB)

Hansson, D. & A. Omstedt (2007): Modelling the Baltic Sea ocean climate on centennial time scale: temperature and sea ice.

Climate Dynamics 30, 763-778

2 Non-Stationarity in Climate Model Simulations

990 year model study from AOGCM Echo-G990 year model study from AOGCM Echo-G

Climate Model Simulations

Climate simulation as a surrogate climate:

- Model = simplified representation of „real“ processes

Idealized pseudo-reconstruction-approach:

- comparison of NAO and CEZI

- use of area weighted t2m of the Baltic catchment area for

reconstructing the NAO by simple linear regression (without

adding white noise)

- comparison with „real“ model NAO

- estimation of non-stationarity for reconstructions within the model

Atmosphere: ECHAM4

T30 (3.75° x 3.75°) 19 vertical layers

Ocean: HOPE-G

Horizontal Resolution 2,81° x 2,81°20 vertical layersincreased tropical resolution

Model description of Echo-G

Settings of Echo-G simulations

Control-run of 1000 model years with fixed present conditions

External forced simulations I: solar + volcanic + greenhouse Gases

ERIK1: 990-1990 A.D. starting with warm ocean as initial condition

ERIK2: 990-1990 A.D. starting with cold ocean as initial condition

External forced simulations II: + orbital forcing

Oetzi1: 7000 B.P. – 1998 A.D. with orbital forcing only

Oetzi2: 7000 B.P. – 1998 A.D. with orbital, solar and greenhouse gases (no volcanic)

NAO vs. Baltic Sea climateexternal forced (solar, volcanic, GHG)

NAO vs. Baltic Sea climateControl-Run

3 Idealized pseudo-proxy reconstruction of NAO from local scale

Idealized pseudo-reconstruction

)()()(^

ttTtNAO Baltic

estimation of NAO from pseudo-proxy

Idealized pseudo-reconstruction

4 Summary

Magnitude of non-stationarity for NAO-impact is high for Baltic Sea areaMagnitude of non-stationarity for NAO-impact is high for Baltic Sea area

- NAO vs. station-temperature 1824-2008 (DJF): RC30 = {10 - 65%}

- NAO vs. sea-ice (MIB) since 1500: RC30 = {0 – 64%}

- NAO vs. t2m (AOGCM) (DJF) since 1000: RC30 = {0 – 64%}

4 Summary

Comparison of external forced simulations with control-run (990 years):

- same magnitude of non-stationarity over time with all/no forcings

- no relationship between forcing and non-stationarity

non-stationarity is mainly result of internal climate variabilitynon-stationarity is mainly result of internal climate variability

possible external influence on longer time scales (orbital changes)?

e.g. Groll et al. (2005): Changes in AO-regional-climate relationship during Eemian (125 kyr BP) compared with pre-industrial (1800 A.D.)

- significantly lower AO-t2m signal for NH winter during Eemian

- also stronger NH winter westerlies towards Europe, warmer CET

Groll, N., Widmann, M., Jones, J., Kaspar, F. & S. Lorenz (2005): Simulated relationship between regional temperatures and large-scale circulation: 125 kyr BP (Eemain) and the preindustrial periodJournal of Climate 2005, 18(19), 4032-4045

References

Cassou, C., L. Terray, J.W. Hurrell and C. Deser (2004): North Atlantic winter climate regimes: spatial asymmetry,

stationarity with time and oceanic forcing, J. Climate, 17, 1055-1068.

Hansson, D. & A. Omstedt (2007): Modelling the Baltic Sea ocean climate on centennial time scale: temperature and sea

ice. Climate Dynamics 30, 763-778

Jacobeit, J., Beck, C. & A. Philipp (1998): Annual to Decadal Variability in Climate in Europe. Würzburger Geographische

Mauskripte, Vol. 43.

Luterbacher, J., Xoplaki, E., Dietrich, D., Rickli, R., Jacobeit, J., Beck, C., Gyalistris, D., Schmutz, C. & H. Wanner (2002):

Reconstruction of sea level pressure fields over Eastern North Atlantic and Europe back to 1500. Clim. Dyn. 18: 545-561.

Osborn, T.J., Briffa, K.R., Tett, S.F.B., Jones, P.D. and R.M. Trigo (1999): Evaluation of the North Atlantic Oscillation as

simulated by a coupled climate model. Climate Dynamics 15, 685-702.

Vicente-Serrano, S. M., and J. I. López-Moreno (2008), Nonstationary influence of the North Atlantic Oscillation on

European precipitation, J. Geophys. Res., 113.

Zorita, E. and F. González-Rouco (2002): Are temperature-sensitive proxies adequate for North Atlantic Oscillation

reconstructions? Geophysical Research Letters, 29 (14), 48-1 - 48-4.

Zorita, E., Gonzalez-Rouco, F. and S. Wagner (2009): Low-frequency response of the Arctic Oscillation to

external forcing in the past millennium. Geophysical Research Letters (submitted).

Thank you for your attention!

Climate is what we expect,

Weather is what we get.

(after Lorenz)

5 Outlook Principal Component Analysis

teleconnection patterns describe the low-frequency extratropical atmosphere generally in terms of space-

stationary and time-fluctuating structures

Stability of SLP-patterns over time:Running EOF

Moving-EOF-analysis with window size a = 31years

Comparison of reference patterns (EOFs over 1000-1998) with subperiods

Field-correlation detected by |scalarproduct| of reference pattern R of the whole time period with each subperiod-EOF S yields |rR,S| = [0,1]

with

|r| = [0,1] due to orthogonality of EOFs

* Field correlations like RunCor(X,Y) of anomaly field with mean

**

*

)()(

),(,

kSR

SRk

YVarXVar

YXCovSRr k

0 kk yx

Slides for Discussion

__Changes of westerly winds in the North Atlantic region_Temporal evolution of the DJF North Atlantic Oscillation Index

Zorita, E., Gonzalez-Rouco, F. and S. Wagner (2009): Low-frequency response of the Arctic Oscillation to external forcing in the past millennium.

Geophysical Research Letters (submitted).

Non-Stationarity in the circulation-climate relationship Stability of NAO-Influence on the Regional...

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