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Dehai Luo, Tingting Gong, and Linhao Zhong

likely due to variations in the north–south position of the jet. However, why the phase of NAO depends on the meridional displacement of the jet is not sufficiently understood. The purpose of this paper is to provide a simple explanation for why the northward (southward) shift of a preexisting jet can excite the positive (negative) phase of the NAO by presenting an analytical solution of topographically forced stationary waves in a specified jet. It is also natural that anticyclonic (cyclonic) wave

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Cheikh O. Mbengue and Tim Woollings

Gray 1986 ; Stephenson 1994 , 1995 ; Robinson 1997 ; Chen et al. 2007 ; Kidston and Vallis 2010 ; Sandu et al. 2016 ; Polichtchouk and Shepherd 2016 ; Pithan et al. 2016 ). One such feature is the eddy-driven jet. Theoretical studies of the eddy-driven jet response to drag focused primarily on global drag variations ( James and Gray 1986 ; Robinson 1997 ; Chen et al. 2007 ; Kidston and Vallis 2010 ; Polichtchouk and Shepherd 2016 ), although counterexamples exist; for example

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D. G. Dritschel and M. E. McIntyre

stratified, rotating systems, are three interrelated phenomena on which this review will focus: first the spatial inhomogeneity of PV mixing by layerwise-two-dimensional turbulence, second the common occurrence of “antifrictional” or upgradient horizontal stresses , and third the spontaneous creation and self-sharpening, or narrowing, of jets. The three phenomena are all illustrated by the typical jet-sharpening scenario sketched in Fig. 1 . The sketch was originally made to help understand the

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Nikolaos A. Bakas, Navid C. Constantinou, and Petros J. Ioannou

1. Introduction Robust eddy-driven zonal jets are ubiquitous in planetary atmospheres ( Ingersoll 1990 ; Ingersoll et al. 2004 ; Vasavada and Showman 2005 ). Laboratory experiments, theoretical studies, and numerical simulations show that small-scale turbulence self-organizes into large-scale coherent structures, which are predominantly zonal and, furthermore, that the small-scale turbulence supports the jets against eddy mixing ( Starr 1968 ; Huang and Robinson 1998 ; Read et al. 2007

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Nikolaos A. Bakas and Petros J. Ioannou

1. Introduction Zonal jets are prominent features of planetary, turbulent flows with well-studied examples being the banded winds of the gaseous planets ( Ingersoll 1990 ). These large-scale flows are maintained by the momentum fluxes of the turbulent eddy field with which they coexist ( Kuo 1951 ; Starr 1968 ; Vasavada and Showman 2005 ) and emerge spontaneously out of a background of homogeneous turbulence both in rotating-tank experiments ( Read et al. 2004 ) and in a large number of

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Ding Ma, Pedram Hassanzadeh, and Zhiming Kuang

1. Introduction The annular mode is a dominant pattern of extratropical circulation variability in both hemispheres on intraseasonal to interannual time scales ( Kidson 1988 ; Thompson and Wallace 1998 ; Gong and Wang 1999 ; Thompson and Wallace 2000 ). The annular mode corresponds to the leading empirical orthogonal function (EOF) of zonal-mean zonal wind, which features an equivalent barotropic dipolar structure and represents latitudinal shifts of the eddy-driven midlatitude jet ( Nigam

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Shin Takehiro, Michio Yamada, and Yoshi-Yuki Hayashi

numerical experiments of decaying turbulence on a rotating sphere with full spherical geometry. They investigated the statistical tendency for the development of a flow field from a random set of initial states and found that a banded structure of zonal flows emerges and that there was a tendency for circumpolar flows to be easterly jets. However, especially in cases when the rotation rate is large, their initial fields are in a state of “wave turbulence”; that is, the initial kinetic energy spectrum is

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I. I. Rypina, M. G. Brown, F. J. Beron-Vera, H. Koçak, M. J. Olascoaga, and I. A. Udovydchenkov

1. Introduction It is now generally accepted that during the austral winter and spring the Southern Hemisphere stratospheric polar vortex provides an effective barrier to meridional transport of passive tracers. During this period winds at high latitudes in the Southern Hemisphere throughout most of the stratosphere are characterized by a nearly zonal jet; the polar vortex can be defined as the region poleward of the jet core, and available evidence suggests that the transport barrier is nearly

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Tim Woollings, Joaquim G. Pinto, and João A. Santos

, Santos et al. (2009) analyzed the occurrence of strong and persistent ridge events (SPREs) over the southeastern North Atlantic and described the associated large-scale meteorological conditions. SPREs are commonly characterized by a strengthening of the North Atlantic ridge, a northward shift of the North Atlantic storm track, and an enhanced diffluence of the subtropical and eddy-driven westerly jets over the North Atlantic. During SPREs there is also clear evidence for a warm-core equivalent

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Gwendal Rivière

1. Introduction Because of increased amounts of greenhouse gases (GHGs), several changes in the atmospheric general circulation have been noted in future climate Intergovernmental Panel on Climate Change (IPCC) scenarios relative to the present climate. Among them, there is a rise in the height of the tropopause ( Lorenz and DeWeaver 2007 ), an increase in the dry static stability ( Yin 2005 ; Frierson 2006 ), and a poleward shift of the tropospheric jet streams and storm tracks. This is seen

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