The formation and breakdown of Kelvin-Helmholtz billows

Readings, C. J.; Atlas, David; Emmanuel, C. B.; Pao, Yih-Ho; Thorpe, S. A.

doi:10.1007/bf02188324

Cited by 7 publications

(6 citation statements)

References 16 publications

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“…We estimate that the overall thickness of the billow structures is limited by the radar resolution, 1 km, and should be larger than the thickness Lmax "' 200 m obtained with the assumption of Ri • l/4. The implied ratio of wavelength to this overall thickness of---1 km falls within the 5-9 range for this ratio given by Reading et al [1973]. Within the limitations of the experiment, it therefore is conceivable that the structures in Plate l d could be a manifestation of Kelvin-Helmholtz billows.…”

Section: Summary and Discussionsupporting

confidence: 55%

“…The fine Doppler resolution observations (Plates lb and l d) often show features remarkably similar to Kelvin-Helmholtz billows that have been observed in shear flow in laboratory and in the atmosphere [Thorpe, 1973]. A characteristic aspect of these billows is that the wavelength of the dominant features should be 5-9 times their overall thickness [Thorpe, 1973;Reading et al, 1973]. The structures seen in Plate lb cannot be interpreted as Kelvin-Helmholtz billows, as their inferred horizontal wavelength of ---50 km would imply a thickness of---5 km, whereas a thickness < 100 m was derived in section 4.…”

Section: Summary and Discussionmentioning

confidence: 58%

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Fine Doppler resolution observations of thin turbulence structures in the tropostratosphere at Millstone Hill

Wand¹,

Rastogi²,

Watkins³

et al. 1983

J. Geophys. Res.

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The 440‐MHz radar at Millstone Hill (42.6°N, 71.5°W) was employed to examine the detailed evolution of turbulence structures in the tropostratosphere with a very fine Doppler resolution of 0.12 Hz, corresponding to 4 cm s−1 radial velocity resolution. The measurement technique involved directing the antenna downwind at a low elevation angle (15° or 20°) and processing the echos from a range where the background wind shear was high. Although no attempt was made to obtain good range resolution, a wide variety of turbulence structures were evident by virtue of their different Doppler shifts in the presence of a high wind shear. Using arguments based on the dominance of ‘shear broadening’ and the required velocity gradient to create instabilities, maximum layer thicknesses in the vicinity of 20–300 m were inferred. The implication of these observations to bulk transport of passive contaminants in the stratosphere is briefly discussed.

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Section: Summary and Discussionsupporting

confidence: 55%

Section: Summary and Discussionmentioning

confidence: 58%

Fine Doppler resolution observations of thin turbulence structures in the tropostratosphere at Millstone Hill

Wand¹,

Rastogi²,

Watkins³

et al. 1983

J. Geophys. Res.

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“…Likewise, the horizontal phase speed of the wave motions was found to agree well with the mean wind at the level of maximum shear[Gossard et al, 1970;Hardy et al, 1973], as anticipated by the Miles-Howard semicircle theorem. Finally, in cases where estimates were made, horizontal wavelengths were found to be in qualitative agreement with those expected from theory, though considerable variability was noted[Readings et al; Browning, 1971], indicating an initial Ri •> 0.10 (seeFigure 3). This is generally consistentwith the minimum Ri estimates of •0.15 based on high-resolution soundings [Browning et al, 1970; Browning, 1971; Emmanuel et al, 1972; Hardy et al, .…”

supporting

confidence: 61%

“…Once initiated, the turbulence rapidly expands throughout the billows, causing regions of relatively large gradients between adjacent billows. On occasion, secondary KH instabilities may develop on these strong gradients [Woods, 1969;Thorpe, 1973b], but these regions are themselves engulfed as the turbulence expands horizontally, as shown in Figure 5…”

Section: Under the Above Assumptions And That Of A Mean State In Hydrmentioning

confidence: 99%

Convective and dynamical instabilities due to gravity wave motions in the lower and middle atmosphere: Theory and observations

Fritts¹,

Rastogi²

1985

Radio Science

315

201

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Dynamical and convective instabilities are two mechanisms that contribute significantly to the dissipation of larger-scale motions and the generation of turbulence in the middle atmosphere. The former are normally due to enhanced velocity shears and/or a local minimum of the static stability either in the mean flow or associated with low-frequency wave motions. The most common dynamical instability is the Kelvin-Helmholtz (KH) instability which is often manifested in the atmosphere as a series of KH billows. Convective instabilities occur where the lapse rate becomes superadiabatic through the action of gravity waves and appear to predominate for high-frequency wave motions. This paper reviews the theory and the observational evidence for both types of instabilities in the lower and middle atmosphere. meridional circulation and thermal structure in the stratosphere and mesosphere due to the convergence of gravity wave momentum flux [Lindzen, 1981;Matsuno, 1982;Holton, 1982Holton, , 1983Dunkerton, 1982]. In order for the momentum and energy transported by wave motions to have a permanent effect on the background flow, however, these motions The mechanisms that contribute most to the dissipation (and saturation) of the dominant gravity wave and tidal motions in the middle atmosphere are thought to be the dynamical and convective instability [Fritts et al., 1984], though other mechanisms are also expected to contribute to the dissipation of individual wave motions under certain circumstances. These include molecular diffusion, radiative damping, inertial instability, and the cascade of wave energy to small scales via nonlinear wave-wave interactions [Phillips, 1960; Bretherton, 1964; McEwan and Robinson, 1975; Weinstock, 1976]. Of these, molecular diffusion, radiative damping, and nonlinear interactions operate most effectively on wave motions with small spatial scales and vertical group velocities [Pitteway and Hines, 1963; Fels, 1984; Mc-Comas and Bretherton, 1977; McComas and Miiller, 1981; Yeh and Liu, 1981]. Thus typical spatial and temporal scales suggest that these competing processes will be relatively less important than dynamical or convective instabilities in the dissipation ofthe dominant wave motions in the middle atmosphere. The available observational data suggest that con-1247 1248 FRITTS AND RASTOGI: INSTABILITIES DUE TO GRAVITY WAVES vective and dynamical instabilities, because of the scales at which they occur, result in considerable turbulence throughout the atmosphere. This turbulence is likewise expected to play a significant role in the vertical transport of heat and atmospheric constituents. Because of their importance in atmospheric dynamics, this paper will review the theoretical basis for and the observational evidence of dynamical and convective instabilities in the lower and middle atmosphere. A primary objective of this work is to provide the reader with the information needed to distinguish between the two instabilities, and thus between their likely causes and effects, in observationa...

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“…Lyulyukin et al [] composited shapes and structures of braid patterns of K‐H billows in the SABL observed by a sodar and found that they frequently appear during the morning and evening transition hours. Readings et al [] summarized scientific issues on formation and breakdown of K‐H billows based on atmospheric observations and laboratory results.…”

Section: Observations Of Waves and Wave‐turbulence Interactionsmentioning

confidence: 99%

Review of wave‐turbulence interactions in the stable atmospheric boundary layer

Sun

Nappo²,

Mahrt

et al. 2015

Reviews of Geophysics

135

124

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Flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods. Understanding turbulence intermittency and wave-turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans. The stable atmospheric boundary layer (SABL) commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces, or even daytime over snow and ice surfaces, and when warm air is advected over cold surfaces. Intermittent turbulence intensification in the SABL impacts human activities and weather variability, yet it cannot be generated in state-of-the-art numerical forecast models. This failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow, in which wave-turbulence interaction is a potential mechanism for turbulence intermittency. A workshop on wave-turbulence interactions in the SABL addressed the current understanding and challenges of wave-turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory, observations, and numerical parameterization. There have been a number of reviews on waves, and a few on turbulence in stably stratified flows, but not much on wave-turbulence interactions. This review focuses on the nocturnal SABL; however, the discussions here on intermittent turbulence and wave-turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general.

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The formation and breakdown of Kelvin-Helmholtz billows

Cited by 7 publications

References 16 publications

Fine Doppler resolution observations of thin turbulence structures in the tropostratosphere at Millstone Hill

Fine Doppler resolution observations of thin turbulence structures in the tropostratosphere at Millstone Hill

Convective and dynamical instabilities due to gravity wave motions in the lower and middle atmosphere: Theory and observations

Review of wave‐turbulence interactions in the stable atmospheric boundary layer

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