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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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Thomas Jung and Peter B. Rhines

nature of the storm track. Meridional transport across a large span of latitude carries cyclonic vorticity as far as the high Arctic, where otherwise anticyclonic vorticity would tend to dominate. (Either potential vorticity stirring by Rossby waves of remote origin or symmetric descent of air cooled by radiation will give an anticyclonic tendency unless opposed by topographic guideways.) Several works have used numerical simulations to describe the effects of Greenland on the circulation

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I. G. Watterson

different regional variations that contribute to an annular EOF. For the Southern Hemisphere (SH), the first EOF of geopotential height analyses (e.g., Kidson 1988b ; Gong and Wang 1999 ) has a clearly annular pattern, at least. Furthermore, the EOF1 of surface pressure, commonly known as the southern annular mode (SAM; Thompson and Wallace 2000 ), appears to be of considerable use in understanding the structure of climate change (e.g., Cai et al. 2003 ). Ultimately, a pattern most warrants a name

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Edwin P. Gerber and Geoffrey K. Vallis

) discussed. These effects will be discussed further below.] They indirectly affect the eddies, however, by changing the position of the critical latitudes of the flow, which influence wave breaking. Linear theory suggests that irreversible mixing—the damping of wave activity—occurs at critical layers where the phase speed of the wave, c , equals that of the mean flow u . Particle displacements, η , scale as ψ /( u − c ), where ψ is the streamfunction perturbation, so that displacements will grow

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