Reflexion and stability of waves in stably stratified fluids with shear flow: a numerical study

Jones, Walter L.

doi:10.1017/s0022112068002119

Cited by 133 publications

(75 citation statements)

References 10 publications

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“…A horizontal surface region can be constructed at the critical layer height to obtain a polar plot ("a blocking diagram") showing the range of azimuthal angles and speeds of gravity waves that are blocked from further upward propagation (Ryan, 1991). Gravity waves with horizontal phase speeds and directions within this region would encounter heavy absorption from a large number of diverse and relatively unstructured mechanisms (Booker and Bretherton, 1967;Hazel, 1967;Jones, 1968;Fritts and Geller, 1976;Fritts, 1978;He et al, 1990) as they approach the critical layer. A horizontal surface can be constructed at the critical layer altitude to obtain a polar plot.…”

Section: The Model For Critical Level Blockingmentioning

confidence: 99%

Studies of the wind filtering effect of gravity waves observed at Allahabad (25.45°N, 81.85°E) in India

Mukherjee

Parihar³

et al. 2010

Earth Planet Sp

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Well-de ned coherent wave sources associated with the passage of short-period gravity waves were observed in all-sky images of OH emission on a total 21 occasions during January to May 2008 at Allahabad (25.45 • N, 81.85• E, dip lat ∼16.49• N) in India. The wave motions exhibited similar spatial and temporal properties during each month, but the north-east ward motions were distinctly dominant in April and May 2008. It is a wellknown theory that the upward propagating gravity waves may be blocked or absorbed at a critical layer. We have computed the magnitude and direction of atmospheric gravity waves subject to blocking by horizontal winds, i.e., critical layer directional ltering. The HWM-93 model (Hedin et al., 1996) was used to compute the two components of neutral wind velocity at Allahabad for the period of observation of gravity waves during March and April 2008. Data from two components of wind velocity were then used to construct the blocking diagrams, which show the directions and apparent phase velocities of wave propagation blocked at a given altitude. The blocking diagrams were then compared with experimental observations of gravity waves in OH airglow to determine the accuracy of the wind model and explain the critical layer theory.

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Section: The Model For Critical Level Blockingmentioning

confidence: 99%

Studies of the wind filtering effect of gravity waves observed at Allahabad (25.45°N, 81.85°E) in India

Mukherjee

Parihar³

et al. 2010

Earth Planet Sp

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“…Furthermore, in the presence of rotation (Jones 1968) or rotation with mean flow vorticity (Kunze 1985), the double singularity of equation 7.6.1 separates into two singularities,…”

Section: Integrated Wave Solutions In An Idealized Mean Flowmentioning

confidence: 99%

Interpretation of equatorial current meter data as internal waves

Blumenthal¹

1987

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Garrett and Munk use linear dynamics to synthesize frequency-wavenumber energy spectra for internal waves (GM72, GM75, GM79). The GM internal wave models are horizontally isotropic, vertically symmetric, purely propagating, and universal in both time and space. This set of properties effectively eliminates all the interesting physics, since such models do not allow localized sources and sinks of energy. Thus an important step in understanding internal wave dynamics is to make measurements of deviations from the simple GM models.This thesis continues the search for deviations from the GM models. It has three advantages over earlier work: extensive data from an equatorial region, long time series (2 years), and relatively sophisticated linear internal wave models. Since the GM models are based on mid-latitude data, having data from an equatorial region which has a strong mean current system offers an opportunity to examine a region with a distinctly different basic state. The longer tilae series mean there is a larger statistical ensemble of realizations, making it possible to detect smaller internal wave signals. The internal wave models include several important extensions to the GM models: horizontal anisotropy and vertical asymmetry, resolution between standing modes and propagating waves, general vertical structure, and kinematic effects of mean shear flow. Also investigated are the effects of scattering on internal waves, effects that are especially strong on the equator because the buoyancy frequency variability is a factor of ten higher than at mid-latitudes.In the high frequency internal wave field considered (frequencies between .125 cph and .458 cph), several features are found that are not included in the GM models. Both the kinematic effects of a mean shear flow and the phase-locking that distinguishes standing modes from propagating waves are observed. There is a seasonal dependence in energy level of roughly 10% of the mean level. At times the wave field is zonally and vertically asymmetric, with resulting energy fluxes that are a small (4% to 10%) fraction of the maximum energy flux the internal wave field could support. The fluxes are, however, as big as many of the postulated sources of energy for the internal wave field.

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“…Overreflection is a process initially noted by Jones (1968), who studied the scattering properties of a shear region with Richardson number less than 1 /4. Jones (1968) found that a gravity wave propagating toward a critical level embedded in a shear region is overreflected (i.e., the reflection coefficient exceeds one) because of extraction of energy from the mean flow.…”

Section: Introductionmentioning

confidence: 99%

The Role of Nonnormality in Overreflection Theory

Bakas

Farrell

2010

Journal of the Atmospheric Sciences

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The role of nonnormality in the overreflection of gravity waves is investigated. In the limit of weak stratification, wave packets having a critical level inside a shear layer of finite depth are reflected with amplified energy. This process, which exhibits the characteristics of stimulated emission, occurs in three stages: first, the incoming wave enters the shear layer and excites nonpropagating perturbations leaning with and against the shear. Subsequently, the energy of perturbations leaning against the shear grows in a manner similar to energy growth of perturbations in constant shear flows, indicating that the Orr mechanism that is slightly modified by stratification underlies the observed growth. Finally, the amplified perturbations excite propagating waves originating from the vicinity of the shear layer boundary. The role of nonnormality in this process is also investigated from the perspective of the associated nonorthogonality of the modes of the dynamical system. It is found that the incident wave packet projects on nonorthogonal analytic modes having the structure of a downward propagating wave in the far field below the shear layer and overreflection expressed by the interaction among these nonorthogonal modes.

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Reflexion and stability of waves in stably stratified fluids with shear flow: a numerical study

Cited by 133 publications

References 10 publications

Studies of the wind filtering effect of gravity waves observed at Allahabad (25.45°N, 81.85°E) in India

Studies of the wind filtering effect of gravity waves observed at Allahabad (25.45°N, 81.85°E) in India

Interpretation of equatorial current meter data as internal waves

The Role of Nonnormality in Overreflection Theory

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