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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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Gang Chen, Isaac M. Held, and Walter A. Robinson

generation: to the extent that wave activity radiates away from this source, eddy momentum fluxes converge into this region, and this momentum is removed from the atmosphere by surface friction through the generation of surface westerlies. Using a global two-level primitive equation model, R97 argues that a reduction in surface drag results, first of all, in an enhancement of the barotropic component of the flow, with relatively modest changes in the baroclinic component. But these changes in

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R. K. Scott and L. M. Polvani

turbulent eddy frequencies and the flow should remain isotropic ( Okuno and Masuda 2003 ; Smith 2004 ; Theiss 2004 ). In the forced-dissipative case, (3) does not determine k Rh a priori, since U generally depends in a nontrivial way on both the energy injection and the large-scale dissipation. In the case L D → ∞, an alternative formulation was proposed by Maltrud and Vallis (1991) that was based instead on the upscale energy flux ε. In an isotropic, energy-cascading inertial range, the

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Thomas Jung and Peter B. Rhines

much of Greenland, and its massive ice cap, a remnant of the last glaciation, is a monument to poleward atmospheric moisture flux, which is concentrated in the Atlantic sector at these latitudes. With a height averaging about 1.5 km and reaching greater than 3.5 km, roughly the 650-hPa level, and with relatively high volume and steep southern termination, its potential effect on the general circulation is great. Yet, lying between 60° and 83°N latitude, it is north of the maximum zonally averaged

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Adam P. Showman

hand, the radiative relaxation acts as a kinetic energy removal mechanism. To see how this operates, imagine an initially balanced flow that experiences radiative relaxation. The relaxation decreases the pressure gradient forces, which then no longer fully balance the Coriolis forces. This unbalanced force component points up-gradient : toward pressure highs and away from pressure lows. A secondary circulation therefore develops that drives fluid toward thick regions and away from thin regions

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Yohai Kaspi and Glenn R. Flierl

planets, the internal heat flux is almost as strong as the solar heat flux (except for Uranus), and the upper-atmosphere meridional temperature gradient is very weak. Consequently baroclinic instability has been assumed to play a minor role in the generation of these jets. However we show that even a weak baroclinic shear can result in substantial zonal flows that are stronger than the eddy field, and moreover baroclinic instability introduces a strong meridional variability in the velocity field. The

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