Climate Modelling Group
School of Earth and Ocean Sciences

Analysis of the Variability of the Arctic Oscillation under Enhanced Greenhouse Warming

Proposal to the Climate Change Action Fund (CCAF)

(Arctic research and monitoring)

INVESTIGATORS: Dáithí A. Stone, University of Victoria

Andrew J. Weaver, University of Victoria

INTRODUCTION:

Much of the long-term atmospheric variability takes the form of persistent and recurring large scale patterns of pressure and circulation anomalies (Wallace & Gutzler, 1981; Barnston & Livezey, 1987; Thompson & Wallace, 1998). Most dominant of these modes in the extratropical Northern Hemisphere is the Arctic Oscillation (AO), which modulates the intensity of the polar vortex. Variations in the AO, and hence the North Atlantic Oscillation (NAO), are related to variations in mean temperature (Hurrell, 1996; Thompson & Wallace, 1998), mean precipitation (Dai et al., 1997; Cayan et al., 1998; Stone et al., 1999), and precipitation intensity (Stone et al., 1999) in the Canadian Arctic. Recently, the AO has tended towards a more the positive phase. General circulation models (GCMs) suggest this may be due to enhanced global warming (e.g. Fyfe et al., 1999), with little change in the amplitude of the AO superimposed on a linear trend which responds to surface warming. One of the aims of this proposal is to examine the variability of a GCM-simulated AO under enhanced greenhouse warming equilibrium climates.

One possible interpretation of climate change due to increasing greenhouse gases is that this change is projected onto the natural modes or dominant patterns of variability of the climate system (e.g., Corti et al., 1999). As noted above, the Arctic Oscillation represents one such mode with the Pacific/North American teleconnection pattern and the Antarctic Oscillation representing other such modes. Inherent in the assumption of this interpretation is that these modes remain as dominant patterns of variability in climates different from today. Another goal of this proposal is to examine this assumption as detailed in the methodology section below.

OBJECTIVES:

We seek funding to support a Ph.D. student (D. Stone) for two years to:

a) Analyse changes in the variability of the AO simulated by the Geophysical Fluid Dynamics Laboratory coupled AOGCM under enhanced greenhouse warming;

b) Compare changes in this variability as the mean background state changes;

c) Examine the ordering, magnitude/structure, and explained variance of the dominant global modes of variability under 1x, 2x and 4xCO2 equilibrium climates.

METHODOLOGY:

Ron Stouffer at the Geophysical Fluid Dynamics Laboratory (GFDL) has recently conducted three multiple millennia length integrations using the GFDL coupled AOGCM, under 1´ , 2´ , and 4´ levels of atmospheric CO2. We have recently acquired the last 1000 years of global annual mean surface air temperature (SAT) and sea level pressure (SLP) from these 5,000 year integrations. We will initially undertake an EOF analysis (e.g. Barnston & Livezey, 1987) of the 1xCO2 control climate fields to: a) compare with existing analyses of these fields done at GFDL; b) determine the dominant patterns, their explained variance and hence their ordering. This same analysis will be repeated on the 2x and 4x CO2 fields.

The relative structure, magnitude and ordering of the EOFs will then be analysed to determine the major changes in variability in equilibrium climates with increased levels of atmospheric CO2. Finally, the 1000-year global 2x and 4x CO2 equilibrium SAT and SLP fields will be projected onto the truncated (e.g., first 10) EOFs of the control climate. This will be done in order to determine whether or not the notion of climate change manifesting itself through changes in present-day natural modes is a meaningful way of interpreting the climate change. These data provide a unique opportunity for the understanding of long term variability currently unavailable from Canadian sources. It is anticipated that once equilibrium results become available from CCCma model integrations a similar analysis will be performed.

NEED FOR CCAF FUNDING:

The proposed work is targeted at the "Arctic Research and Monitoring" call for proposals. It will provide short term results that will contribute greatly to our understanding of possible changes in the variability of Arctic climate under enhanced global warming. The data have recently been provided to us by Ron Stouffer at GFDL and we are poised to commence their analysis.

EXPERTISE:

The collaborators in this proposal bring the required expertise for this project. D. Stone recently completed his M.Sc. thesis under the supervision of A. Weaver. In his thesis he undertook a detailed statistical analysis of trends in extreme events within the Canadian historical precipitation record. A. Weaver has a great deal of experience in the analysis of the results from and development of coupled atmosphere ocean sea-ice models. He is currently the lead principal investigator of the AES Arctic node and sits on numerous international and national climate research committees.

DELIVERABLES:

At the end of the two-year funding period this project will have produced important predictions and understanding of possible changes in Arctic climate variability under enhanced greenhouse warming. In particular at least one manuscript will have been submitted to the peer-reviewed scientific literature.

BUDGET:

Description Year 1

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Salary for Ph.D. student (D. Stone) at approved NSERC rate $16 500

Travel for D. Stone to GFDL for collaborative discussions with R. Stouffer. $ 1 500

Operating costs (phone fax computer costs etc) $ 1 000

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Total $19 000

 

Description Year 2

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Salary for Ph.D. student (D. Stone) at approved NSERC rate $16 500

Travel for D. Stone to CMOS conference $ 1 500

Operating costs (phone fax computer costs etc) $ 1 000

Publication charges $ 2 000

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Total $21 000

LEVERAGE:

The leveraging is as follows:

· The model output necessary for this project have already been provided to us. Collaboration with R. Stouffer comes at no cost.

· Computing hardware support are covered from other sources.

· A. Weaver will have NSERC Strategic support during this period (~$150,000 pa) during the duration of this project. The CCAF will be added as a new partner to this project. In addition, this project will be closely linked in with the AES Arctic node (with collaborators G. Flato, E. Carmack, L. Mysak) which is independently funded.

PROJECT MANAGEMENT:

The project will be co-ordinated by A. Weaver, with funds deposited in a University of Victoria account. D. Stone will be supervised by A. Weaver as a Ph.D. student based at the University of Victoria. Drs. F. Zwiers and J. Fyfe will be asked to serve on D. Stone’s Ph.D. committee.

REFERENCES:

Barnston, A. G., and R. E. Livezey. 1987. Classification, seasonality and persistence of low-frequency atmospheric circulation patterns. Mon. Wea. Rev., 115: 1083-1126.

Cayan, D. R.; M. D. Dettinger, H. F. Diaz, and N. E. Graham. 1998. Decadal variability of precipitation o

ver western North America. J. Climate, 11: 3148-3166.

CORTI, S.; F. MOLTENI, and T.N. PALMER. 1999. Signature of recent climate change in frequencies of natural atmospheric circulation regimes . Nature 398: 799-802.

Dai, A.; I. Y. Fung, and A. D. Del Genio. 1997. Surface observed global land precipitation variations during 1900-88. J. Climate, 10: 2943-2962.

FYFE, J. C.; G. J. BOER, and G. M. FLATO. 1999. The Arctic and Antarctic Oscillations and their projected changes under global warming. Geophys. Res. Lett., 26: 1601-1604.

Hurrell, J. W. 1996. Influence of variations in extratropical wintertime teleconnections on Northern Hemisphere temperature. Geophys. Res. Lett., 23: 665-668.

STONE, D. A.; A. J. WEAVER, and F. W. ZWIERS. 1999. Trends in Canadian precipitation intensity. Atmos.-Ocean, submitted.

THOMPSON, D. W. J., and J. M. WALLACE. 1998. The Arctic Oscillation signature in the wintertime geopotential height and temperature fields. Geophys. Res. Lett., 25: 1297-1300.

Wallace, J. M., and D. S. Gutzler. 1981. Teleconnections in the geopotential height field during the Northern Hemisphere winter. Mon. Wea. Rev., 109: 784-812.


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