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Y. D. Afanasyev, P. B. Rhines, and E. G. Lindahl

coastal currents were studies in the laboratory by Griffiths and Linden (1981) . In their experiments the buoyant fluid was released uniformly along the cylindrical boundary. The wavelength and phase velocity of the developing baroclinic instability were measured and compared with a theoretical model that included a two-layer wedge-shaped fluid in a channel with frictional dissipation due to Ekman layers. They demonstrated that the current became unstable when it reached a width at which the critical

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John A. Knox, Donald W. McCann, and Paul D. Williams

1938 ; Cahn 1945 ) and from boundary condition perturbations leading to topographically forced gravity waves ( Smith 1979 ). Instead, it is fundamentally rooted in the “universal ‘internal’ . . . nonlinearity of atmospheric motions,” as demonstrated by Medvedev and Gavrilov (1995) in their independent extension of Lighthill’s theory. While the weakness of spontaneous emission in Lighthill–Ford theory is sometimes emphasized, in this paper we stress the fact that the theory does indeed predict

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Shuguang Wang, Fuqing Zhang, and Chris Snyder

generation evolves very slowly in time (up to many inertial periods) and is nearly steady in an appropriate frame of reference. The inertia wave packets were first noticed by Viúdez (2006) and further examined in Viúdez (2007 , 2008 ). In these studies, Viúdez considered vortex dipoles associated with potential vorticity (PV) anomalies in the interior of the flow rather than confined to a horizontal boundary. Despite the simplified setting of the vortex dipole, the continuous generation of inertia

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David A. Schecter

temperature) of the atmosphere increases monotonically with altitude and that the axisymmetric PV distribution q ( r , θ ) of the unperturbed cyclone decreases monotonically with radius on a surface of constant θ . With suitable boundary conditions, such a vortex is stable in the context of balanced dynamics ( Montgomery and Shapiro 1995 ; Ren 1999 ). On the other hand, stability is not guaranteed when IG waves are allowed to interact with DVRWs—in which case SI can occur. a. PV and angular

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Michael E. McIntyre

, shows the streamwise vertical midplane for a dipole structure induced mainly by a distribution of potential-temperature anomalies on a solid bottom boundary z = 0. This is equivalent to a Bretherton PV delta function. The interior PV is isentropically uniform, to a first approximation. The faint thick contour on the right of the top left panel marks the separatrix or | v | = 0 isotach in the comoving reference frame, where | v | is horizontal flow speed. The other contours are the isotachs for

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Norihiko Sugimoto, Keiichi Ishioka, and Katsuya Ishii

power of U 0 . 4. Results a. Typical gravity wave radiation (Ro = 100, Fr = 0.3) First, the results for the case of Ro = 100 and Fr = 0.3 are shown. In a previous study we adopted these parameter values using the numerical model in a doubly periodic domain ( Sugimoto et al. 2007b ). In the present study, since the numerical model has no gravity wave reflection at the boundary, it is easy to see the characteristics of spontaneous gravity wave radiation. Figure 2 shows the time evolution of the

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K. Ngan, P. Bartello, and D. N. Straub

. Phys. Fluids , 10 , 3178 – 3184 . McWilliams , J. C. , M. J. Molemaker , and I. Yavneh , 2004 : Ageostrophic, anticyclonic instability of a geostrophic, barotropic boundary current. Phys. Fluids , 16 , 3720 – 3725 . Molemaker , M. J. , J. C. McWilliams , and I. Yavneh , 2005 : Baroclinic instability and loss of balance. J. Phys. Oceanogr. , 35 , 1505 – 1517 . Ngan , K. , D. N. Straub , and P. Bartello , 2004 : Three-dimensionalization of freely-decaying two

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Yonghui Lin and Fuqing Zhang

Mesoscale Model (MM5; Dudhia 1993). Three two-way-nested model domains (D1, D2, and D3) respectively use 90-, 30-, and 10-km horizontal grid spacing, and 60 vertical layers are used with 360-m vertical spacing. D1 is configured in the shape of a channel 27 000 km long ( x direction) and 8010 km wide ( y direction), and D2 (D3) is a rectangular subdomain 9300 (3100) km long and 4500 (2500) km wide centered at x = 6150 (17 000) km and y = 2850 (6700) km within D1 (D2). Radiative top boundary

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Kaoru Sato and Motoyoshi Yoshiki

studies have been performed to elucidate the role of gravity waves in the atmosphere (see Fritts 1984a and Fritts and Alexander 2003 for reviews). Currently gravity waves are recognized as one of primary components of atmospheric dynamics, particularly for the middle atmosphere. The weak wind layer around the mesopause at middle latitudes is maintained by the mean wind deceleration force associated with the breaking and/or dissipation of gravity waves ( Lindzen 1981 ; Matsuno 1982 ). Through the

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J. Vanneste

at Manoa, 59–66 . McWilliams , J. C. , M. J. Molemaker , and I. Yavneh , 2004 : Ageostrophic, anticyclonic instability of a geostrophic, barotropic boundary current. Phys. Fluids , 16 , 3720 – 3725 . Mohebalhojeh , A. R. , and D. G. Dritschel , 2001 : Hierarchies of balance conditions for the f -plane shallow water equations. J. Atmos. Sci. , 58 , 2411 – 2426 . Molemaker , M. J. , J. C. McWilliams , and I. Yavneh , 2001 : Instability and equilibration of

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