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John Marshall, David Ferreira, J-M. Campin, and Daniel Enderton

set up annular modes in the zonal jets of the ocean. The ultimate source of the variability of the coupled system is the “shake” due to the interaction between atmospheric synoptic systems with the atmospheric zonal jet. However, we find that coupling between the annular modes in the two fluids leads to a distinct decadal signal in both fluids. A simple stochastic model of the observed variability is developed and captures the essence of the coupled mechanism. In section 4 we conclude

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Robert X. Black and Brent A. McDaniel

weather ( Thompson and Wallace 2001 ; Baldwin et al. 2003 ). These annular modes occur in both the Northern and Southern Hemispheres [i.e., the Northern Annular Mode (NAM) and the Southern Annular Mode (SAM)] and over a wide range of time scales (weeks to decades). Most recent research examining connections between the stratospheric polar vortex and tropospheric circulation patterns has focused on either subseasonal variability (e.g., Limpasuvan et al. 2004 ; McDaniel and Black 2005 ) or long

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I. G. Watterson

1. Introduction “What is meant by the words annular and mode?” asked Ambaum et al. (2001 , p. 3506), with respect to atmospheric variability. This is a fair question, since the words are hard to find in meteorological glossaries. A typical dictionary will offer “ring-shaped” and “most frequent value in a dataset” (matching the meaning for mode given in the American Meteorological Society Glossary of Meteorology ). A geographical pattern of variability that features a zonal band does form a

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Michael J. Ring and R. Alan Plumb

1. Introduction The low-frequency patterns known as the annular modes have attracted an increasing amount of research interest in recent years. While the annular modes are the leading patterns of extratropical variability in both hemispheres on a month-to-month time scale ( Thompson and Wallace 1998 , 2000 ), their behavior may also be important for deciphering changes over longer periods, such as decadal climate trends ( Thompson et al. 2000 ). The patterns are remarkably robust, and though

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Robert X. Black and Brent A. McDaniel

tropospheric weather conditions ( Thompson and Wallace 2001 ; Baldwin et al. 2003 ). Also, polar vortex variations have been linked to regional variability in column ozone and incoming UV flux at the earth’s surface ( Karpetchko et al. 2005 ). Although annular modes occur over a wide range of time scales (weeks to decades), there has been a substantial focus on subseasonal variability (e.g., Limpasuvan et al. 2004 ; McDaniel and Black 2005 , hereafter MB ) and long-term trends ( Thompson and Solomon

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