Persistence of a Kelvin‐Helmholtz instability complex in the upper troposphere

Kelley, M. C.; Chen, C. Y.; Beland, Robert R.; Woodman, R. F.; Chau, Jorge L.; Werne, J.

doi:10.1029/2004jd005345

Cited by 29 publications

(26 citation statements)

References 12 publications

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“…A similar evolution of a shear flow region was reported using radar and balloon data from the upper troposphere (Kelley et al, 2005). In this case, shear was disrupted over many hours by localized instabilities due to gravity waves.…”

Section: Discussionsupporting

confidence: 49%

Eddy turbulence parameters inferred from radar observations at Jicamarca

2007

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Abstract. Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007). In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1×10 3 m 2 /s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007) is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density.

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Section: Discussionsupporting

confidence: 49%

Eddy turbulence parameters inferred from radar observations at Jicamarca

2007

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“…Under stably stratified conditions, geophysical turbulence can only arise from dynamical processes leading to instability at sufficiently high Reynolds numbers. These include shear flows having sufficiently low Ri and high Re and 2D or 3D GW motions that can induce instability at essentially all GW frequencies and amplitudes for sufficiently high Re [see, e.g., Fritts and Rastogi , 1985; Thorpe , 1987; Klostermeyer , 1991; Lombard and Riley , 1996; Sonmor and Klaassen , 1997; Kelley et al , 2005; Achatz , 2005, 2007; Achatz and Schmitz , 2006a, 2006b]. As a result of these various sources, significant turbulence tends to be intermittent and layered, with the turbulence fraction and intensity being functions of the sources and environment [e.g., Crane , 1980; Dewan , 1981; Barat , 1982; Sato and Woodman , 1982; Hocking , 1985; Alisse and Sidi , 2000; Fritts et al , 2003, and references therein].…”

Section: Discussionmentioning

confidence: 99%

“…Of the overall turbulence occurrences throughout the atmosphere, KHI likely accounts for a significant fraction, given the dominant contributions of low‐frequency inertia‐GWs to horizontal winds and wind shears that favor the tendency for KHI rather than GW breaking in such environments [ Fritts et al , 2003]. We also anticipate that KHI throughout the atmosphere will contribute preferentially to radar backscatter and associated measurement biases, given the tendency for more significant temperature and refractive index structure function, C T 2 and C N 2 , enhancements at the edges of KHI mixing layers than accompanying turbulence due to GW breaking [e.g., Coulman et al , 1995; Werne and Fritts , 1999a, 2000, 2001; Kelley et al , 2005; Strelnikov et al , 2009]. As a result, we expect radar measurement biases to accompany a large fraction of radar measurements, especially where high radar sensitivity allows measurements to late stages in the turbulence evolution.…”

Section: Discussionmentioning

confidence: 99%

Computation of clear‐air radar backscatter from numerical simulations of turbulence: 3. Off‐zenith measurements and biases throughout the lifecycle of a Kelvin‐Helmholtz instability

et al. 2012

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[1] Previous papers by Franke et al. (2011) and Fritts et al. (2011) described the computation of radar backscatter power and vertical velocities from numerical simulations of turbulence arising due to Kelvin-Helmholtz (KH) shear instability. Comparisons of backscatter power and inferred velocities with the distributions of turbulence and the true velocities revealed biases in the identification of active or intense turbulence and in the inferred Doppler spectrum and vertical velocities throughout the flow evolution. This paper extends these analyses to off-zenith viewing angles typical of multiple-beam MF, HF, and VHF radars. These reveal similar biases in the identification of turbulence occurrence, Doppler spectra, and inferred radial velocities, with additional sensitivity to the off-zenith angle relative to the mean shear across the turbulence layer. Radial velocities are typically underestimated during turbulence generation and breakdown of the KH billows, except where turbulence refractive index gradients are strong. Doppler spectra are biased toward regions retaining strong refractive index gradients, implying strong aspect sensitivity at later stages in the evolution. Persistent tilted structures at late stages of the evolution contribute to radial velocity measurement biases that also are functions of off-zenith angle and time.

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“…Mesosphere‐stratosphere‐troposphere (MST) radars can also be used for studying KH instabilities in the atmosphere [e.g., Röttger and Schmidt , 1979; VanZandt et al , 1979; Klostermeyer and Rüster , 1980, 1981; Singh et al , 1999; Yamamoto et al , 2003; Kelley et al , 2005]. The development of frequency domain interferometry (FDI) techniques (using two carrier frequencies or more and devoted to improve the range resolution of the MST radars) allowed direct observations of KH billows [e.g., Chilson et al , 1997, 2003; Luce et al , 2007, 2008].…”

Section: Introductionmentioning

confidence: 99%

Observations of Kelvin‐Helmholtz instability at a cloud base with the middle and upper atmosphere (MU) and weather radars

et al. 2010

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[1] Using the very high frequency (46.5 MHz) middle and upper atmosphere radar (MUR), Ka band (35 GHz) and X band (9.8 GHz) weather radars, a Kelvin-Helmholtz (KH) instability occurring at a cloud base and its impact on modulating cloud bottom altitudes are described by a case study on 8 October 2008 at the Shigaraki MU Observatory, Japan (34.85°N, 136.10°E). KH braids were monitored by the MUR along the slope of a cloud base gradually rising with time around an altitude of ∼5.0 km. The KH braids had a horizontal wavelength of about 3.6 km and maximum crest-to-trough amplitude of about 1.6 km. Nearly monochromatic and out of phase vertical air motion oscillations exceeding ±3 m s −1 with a period of ∼3 min 20 s were measured by the MUR above and below the cloud base. The axes of the billows were at right angles of the wind and wind shear both oriented east-north-east at their altitude. The isotropy of the radar echoes and the large variance of Doppler velocity in the KH billows (including the braids) indicate the presence of strong turbulence at the Bragg (∼3.2 m) scale. After the passage of the cloud system, the KH waves rapidly damped and the vertical scale of the KH braids progressively decreased down to about 100 m before their disappearance. The radar observations suggest that the interface between clear air and cloud was conducive to the presence of the dynamical shear instability by reducing static stability (and then the Richardson number) near the cloud base. Downward cloudy protuberances detected by the Ka band radar had vertical and horizontal scales of about 0.6-1.1 and 3.2 km, respectively, and were clearly associated with the downward air motions. Observed oscillations of the reflectivity-weighted Doppler velocity measured by the X band radar indicate that falling ice particles underwent the vertical wind motions generated by the KH instability to form the protuberances. The protuberances at the cloud base might be either KH billow clouds or perhaps some sort of mamma. Reflectivity-weighted particle fall velocity computed from Doppler velocities measured by the X band radar and the MUR showed an average value of 1.3 ms −1 within the cloud and in the protuberance environment.

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Persistence of a Kelvin‐Helmholtz instability complex in the upper troposphere

Cited by 29 publications

References 12 publications

Eddy turbulence parameters inferred from radar observations at Jicamarca

Eddy turbulence parameters inferred from radar observations at Jicamarca

Computation of clear‐air radar backscatter from numerical simulations of turbulence: 3. Off‐zenith measurements and biases throughout the lifecycle of a Kelvin‐Helmholtz instability

Observations of Kelvin‐Helmholtz instability at a cloud base with the middle and upper atmosphere (MU) and weather radars

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