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GEOPHYSICAL RESEARCH LETTERS, VOL. 28, NO. 6, PAGES 1019–1022, 2001

The Preferred Structure of Variability of the Northern Hemisphere Atmospheric Circulation

A. H. Monahan

Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada

L. Pandolfo

Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada

J. C. Fyfe

Canadian Centre for Climate Modelling and Analysis, Meteorological Service of Canada, University of Victoria, Victoria, BC, Canada

Abstract

A nonlinear generalisation of Principal Component Analysis (PCA) is applied to the 500mb geopotential height field of the Northern Hemisphere extratropical atmosphere. It is found that the low-frequency variability of the mid-troposphere is characterised by three distinct quasi-stationary states. The states are described and compared to those obtained from applications of cluster analyses and linear PCA to the height field. Evidence is provided that modes obtained through PCA (notably the Arctic Oscillation (AO)) are not independent dynamical modes of variability of the Northern Hemisphere extratropics. Rather they arise as the optimal linear compromise between the preferred quasi-stationary states of the circulation.

Received 20 July 2000; accepted 19 December 2000.

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Citation: Monahan, A. H., L. Pandolfo, and J. C. Fyfe (2001), The Preferred Structure of Variability of the Northern Hemisphere Atmospheric Circulation, Geophys. Res. Lett., 28(6), 1019–1022.

Copyright 2001 by the American Geophysical Union.