Evolution and Breakdown of Kelvin–Helmholtz Billows in Stratified Compressible Flows. Part II: Instability Structure, Evolution, and Energetics

Palmer, Teresa Lynne; Fritts, David C.; Andreassen, Øyvind

doi:10.1175/1520-0469(1996)053<3192:eabokb>2.0.co;2

Cited by 50 publications

(60 citation statements)

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“…As described by Hecht et al (2005), the lifetime of such KH billows is a few tens of minutes. Theoretical studies by Fritts et al (1996) and Palmer et al (1996) show that the lifetime and evolution of such KH billows and their subsequent dissipation are complex and far less understood.…”

Section: Lifetime Of the Deformed Kh Billowmentioning

confidence: 99%

A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India

et al. 2015

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The height-time-concentration map of neutral sodium (Na) atoms measured by a Na lidar during the night of 18 to 19 March 2007 over Gadanki, India (13.5°N, 79.2°E) reveals an unusual structure in the Na layer for around 30 min in the altitude range of 92 to 98 km which is similar to the usual 'C' type structures observed at other locations. In order to understand the physical mechanism behind the generation of this unusual event, an investigation is carried out combining the data from multiple instruments that include the meteor wind radar over Thiruvananthapuram, India (8.5°N, 77°E) and the SABER instrument onboard the TIMED satellite. The temperature and wind profiles from the data set provided by these instruments allow us to infer the Richardson number which is found to be noticeably less than the canonical threshold of 0.25 above 92 km over Thiruvananthapuram suggesting the plausible generation of Kelvin-Helmholtz (KH) billows over southwestern part of the Indian subcontinent. Based on the average wind speed and direction over Thiruvananthapuram, it is proposed that the KH-billow structure was modified due to the background wind and was advected with it in nearly 'frozen-in' condition (without significant decay) in the northeastward direction reaching the Na lidar location (Gadanki). This case study, therefore, presents a scenario wherein the initially deformed KH-billow structure survived for a few hours (instead of a few minutes or tens of minutes as reported in earlier works) in an apparently 'frozen-in' condition under favorable background conditions. In this communication, we suggest a hypothesis where this deformed KH-billow structure plays crucial role in creating the abovementioned unusual structure observed in the Na layer over Gadanki.

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Section: Lifetime Of the Deformed Kh Billowmentioning

confidence: 99%

A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India

et al. 2015

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“…At these times there are increasingly sharp potential-temperature and velocity gradients caused by fluid entrainment and baroclinic torques acting on mass-density gradients within the entraining fluid. Thereafter, streamwise-aligned, counter-rotating vortices quickly arise within the outer billow (Klaassen and Peltier, 1985), where the fluid is both convectively and inertially unstable Palmer et al, 1996). The close proximity of the convectively unstable layers and adjacent sheared stable layers leads to orthogonal vortex alignments, loop vortices, and the vortex interactions and twist-wave dynamics that have been seen in related wave-breaking dynamics to drive the turbulence cascade towards ever smaller scales of motion (Arendt et al, 1997;Andreassen et al, 1998;Fritts et al, 1998).…”

Section: Simulation Of Turbulence Caused By Kelvinhelmholtz Instabilitymentioning

confidence: 98%

Turbulence-induced fluctuations in ionization and application to PMSE

Hill

Gibson-Wilde²,

Werne³

et al. 2014

Earth Planet Sp

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The temporal evolution of a turbulent layer is calculated in detail by solving the hydrodynamic equations. The turbulence is initiated by a Kelvin-Helmholtz instability. The field of potential-temperature fluctuations serves as a tracer for modeling entrainment of the mixing ratios of ionized constituents hypothesized to be present in the upper polar mesosphere. This entrainment modeling provides the input to a turbulence advection model capable of calculating the spectra and cospectra of ions and electrons. The turbulence advection model is used as a subgrid-scale model and is required because, given present or foreseeable computer capabilities, numerical solutions cannot span the enormous range of spatial scales from the depth of the shear layer to the smallest scales on which the most massive ions diffuse. The power spectrum of electron number-density fluctuations obtained from the turbulence advection model is compared with that measured by a rocket during the STATE (Structure and Atmospheric Turbulence Environment) experiment; agreement is found for a case of massive ions. The radar cross section for Bragg scattering is calculated from the electron number-density power spectrum and is used to calculate the signal-to-noise ratio (S/N) for the Poker Flat 50 MHz radar. The resultant S/N is then compared with the radar measurements obtained during the STATE experiment. These comparisons support the hypothesis that massive ions can cause polar mesosphere summer echoes from turbulent layers. Large-scale morphology of the turbulent layer obtained from rocket and radar measurements is reproduced by the hydrodynamic solution.

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“…Patnaik et al, 1976;Klaassen and Peltier, 1985;Palmer et al, 1996;Fritts et al, 1996). The evolution of KH billows will also be described by the potential temperature in this paper for the following two reasons.…”

Section: The Evolution Of Kh Billowsmentioning

confidence: 99%

“…In addition, the models developed by Peltier (1985a, b, 1991) (hereinafter designated KP) and Hill et al (1999) and Werne and Fritts (1999) (hereinafter designated HW) were all performed using the shear horizontal wind and temperature background fields, and the KH billows were excited by a small amplitude stochastic perturbation. Similarly, the shear horizontal field models were used by Fritts et al (1996) and Palmer et al (1996) (hereinafter designated FP), where KH billows were excited by a regular vertical velocity perturbation. The shear horizontal wind method was also employed by Fritts et al (2003) to simulate KH instabilities.…”

Section: Introductionmentioning

confidence: 99%

Kelvin-Helmholtz billows and their effects on mean state during gravity wave propagation

Liu

Gao

et al. 2009

Ann. Geophys.

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Abstract. The Kelvin-Helmholtz (KH) billows which appear in the process of gravity wave (GW) propagation are simulated directly by using a compressible nonlinear twodimensional gravity wave model. The differences between our model and others include: the background field has no special initial configuration and there is no initial triggering mechanism needed in the mesosphere and lower thermosphere (MLT) region to excite the KH billows. However, the initial triggering mechanism is performed in the lower atmosphere through GW, which then propagate into the MLT region and form billows. The braid structures and overturning of KH billows, caused by nonlinear interactions between GWs and mean flow, can be resolved precisely by the model. These results support the findings in airglow studies that GWs propagating from below into the MLT region are important sources of KH billows. The onset of small scale waves and the wave energy transfer induce the shallower vertical wave number power spectral densities (PSD). However, most of the slopes are steeper than the expected k −3 z power law, which indicates that GWs with 10 km vertical wavelength are still a dominant mode. The results also show that the evolution of mean wind vary substantially between the different processes of GWs propagation. Before the KH billows evolve, the mean wind is accelerated greatly by GWs. By contrast, as the KH billows evolve and mix with mean flow, the mean wind and its peak value decrease.

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Evolution and Breakdown of Kelvin–Helmholtz Billows in Stratified Compressible Flows. Part II: Instability Structure, Evolution, and Energetics

Cited by 50 publications

References 0 publications

A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India

A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India

Turbulence-induced fluctuations in ionization and application to PMSE

Kelvin-Helmholtz billows and their effects on mean state during gravity wave propagation

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