Air motion within Kelvin‐Helmholtz billows determined from simultaneous Doppler radar and aircraft measurements

Browning, K. A.; BRYANT, GW; Starr, J. R.; Axford, D. N.

doi:10.1002/qj.49709942203

Cited by 43 publications

(14 citation statements)

References 16 publications

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“…Also evident are small‐scale temperature fluctuations with a horizontal ground‐based wavelength of approximately 1 km (e.g., at 50 km flight distance). These are likely to be a signature of Kelvin‐Helmholtz billows appearing during the transition to turbulent flow [ Browning et al , 1973]. It is interesting to note that these small‐scale waves exhibit a striking sawtooth waveform on closer inspection.…”

Section: Observationsmentioning

confidence: 99%

Airborne observations of turbulence, mixing, and gravity waves in the tropopause region

et al. 2002

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[1] In situ observations of small-scale dynamics and compositional structure in the tropopause region are presented. The measurements were made aboard the Grob ''Egrett'' high-altitude research aircraft above Aberystwyth, Wales, in the summer of 2000. The observations presented here show evidence of mixing of ozone and water vapor in a patch of intense turbulence just above the tropopause. This turbulence is shown to be the result of wind shear above a tropospheric jet stream. The value of the vertical eddy diffusion coefficient in this turbulence is estimated to be 0.9 m 2 s À1 . It is also shown that wavelike perturbations superimposed on the overall tracer structure can be accounted for by a gravity wave.

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Section: Observationsmentioning

confidence: 99%

Airborne observations of turbulence, mixing, and gravity waves in the tropopause region

et al. 2002

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“…KelvinHelmholtz (KH) instabilities (Browning et al 1973;Lilly 1986;Fritts et al 2003), mountain waves (Scorer 1949;Durran 1986;Cohn et al 2011), and convective clouds (MacCready 1964;MacPherson and Isaac 1977) are widely known to generate turbulence encountered in flight. Other causes have been recently studied.…”

Section: Introductionmentioning

confidence: 99%

The Generation of Turbulence below Midlevel Cloud Bases: The Effect of Cooling due to Sublimation of Snow

Kudo¹

2013

Journal of Applied Meteorology and Climatology

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In the author's experience as a forecaster, commercial aircraft sometimes report turbulence beneath midlevel clouds that extend above upper frontal zones. Turbulence caused by Kelvin-Helmholtz instability occurs in upper frontal zones with strong vertical shear of horizontal winds. However, the turbulence seems to occur not only in the cloud bases (where upper frontal zones are) but also below the cloud bases where the vertical shear is not strong. Because those clouds are usually accompanied by precipitation that does not reach the ground, cooling by evaporation or sublimation seems to contribute to the generation of turbulence. In this paper, the mechanisms generating turbulence below midlevel cloud bases are examined by using observations and high-resolution three-dimensional numerical simulations with idealized initial conditions. The numerical simulations showed that the following sequence of events led to turbulence. Falling snow sublimated below cloud bases and cooled the air, which created absolute instability. This generated Rayleigh-Bé nard convection cells. The vertical motion caused turbulence. The horizontal scale of the convection was about 800-1000 m, and the variations of vertical wind velocity were up to about 7 m s 21 . The cloud base was accompanied by a virga-like distribution of snow. Sensitivity experiments showed the appropriate conditions to cause the turbulence: 1) the cloud-base temperature was between about 08 and 2158C, 2) the relative humidity in subcloud layers was sufficiently low, and 3) the stability in subcloud layers was weak. The results of the numerical simulations agreed well with the observations.

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“…Readings et al (1973) also hypothesised the possibility of the presence of trapped gravity waves within an inversion. Air motions within KH billows at a height of ≈7 km were investigated by Browning et al (1973b) using radar, aircraft and radiosonde measurements. Undulations of an inversion layer overlying convection during the morning hours were also observed by means of a sodar by Taconet and Weill (1983), with periods of 5-7 min.…”

Section: Introductionmentioning

confidence: 99%

Wavelike Structures in the Turbulent Layer During the Morning Development of Convection at Dome C, Antarctica

Petenko

Argentini

Casasanta

et al. 2016

Boundary-Layer Meteorol

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In the period January-February 2014, observations were made at the Concordia station, Dome C, Antarctica to study atmospheric turbulence in the boundary layer using a high-resolution sodar. The turbulence structure was observed beginning from the lowest height of about 2 m, with a vertical resolution of less than 2 m. Typical patterns of the diurnal evolution of the spatio-temporal structure of turbulence detected by the sodar are analyzed. Here, we focus on the wavelike processes observed within the transition period from stable to unstable stratification occurring in the morning hours. Thanks to the high-resolution sodar measurements during the development of the convection near the surface, clear undulations were detected in the overlying turbulent layer for a significant part of the time. The wavelike pattern exhibits a regular braid structure, with undulations associated with internal gravity waves attributed to Kelvin-Helmholtz shear instability. The main spatial and temporal scales of the wavelike structures were determined, with predominant periodicity of the observed wavy patterns estimated to be 40-50 s. The horizontal scales roughly estimated using Taylor's frozen turbulence hypothesis are about 250-350 m.

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Air motion within Kelvin‐Helmholtz billows determined from simultaneous Doppler radar and aircraft measurements

Cited by 43 publications

References 16 publications

Airborne observations of turbulence, mixing, and gravity waves in the tropopause region

Airborne observations of turbulence, mixing, and gravity waves in the tropopause region

The Generation of Turbulence below Midlevel Cloud Bases: The Effect of Cooling due to Sublimation of Snow

Wavelike Structures in the Turbulent Layer During the Morning Development of Convection at Dome C, Antarctica

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