Interplay of waves and eddies in rotating stratified turbulence and the link with kinetic-potential energy partition

Marino, Raffaele; Rosenberg, Duane; Herbert, Corentin; Pouquet, A.

doi:10.1209/0295-5075/112/49001

Cited by 40 publications

(36 citation statements)

References 42 publications

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“…For F r 0.05 we find a saturation valueΓ 0 ∼ 10 −1 , compatible with the proxy of the mixing efficiency commonly used in the ocean community (≈ 0.2) [27].Γ exhibits as well a non-monotonic dependence on the buoyancy Reynolds number (see table I), with a peak value obtained for R B ∼ 200, consistently with [25]. To complement our characterization of the mixing, we finally evaluated for all runs the ratio of the volume-averaged kinetic to potential energies E V /E P , which can be linked to wave-eddy partition [28]. This quantity is plotted in the insert of Fig.…”

Section: Overturning Regions Vertical Draftsmentioning

confidence: 99%

Vertical drafts and mixing in stratified turbulence: Sharp transition with Froude number

Feraco¹,

Marino²,

Pumir³

et al. 2018

EPL

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We investigate the large-scale intermittency of vertical velocity and temperature, and the mixing properties of stably stratified turbulent flows using both Lagrangian and Eulerian fields from direct numerical simulations, in a parameter space relevant for the atmosphere and the oceans. Over a range of Froude numbers of geophysical interest (≈ 0.05 − 0.3) we observe very large fluctuations of the vertical components of the velocity and the potential temperature, localized in space and time, with a sharp transition leading to non-Gaussian wings of the probability distribution functions. This behavior is captured by a simple model representing the competition between gravity waves on a fast time-scale and nonlinear steepening on a slower time-scale. The existence of a resonant regime characterized by enhanced large-scale intermittency, as understood within the framework of the proposed model, is then linked to the emergence of structures in the velocity and potential temperature fields, localized overturning and mixing. Finally, in the same regime we observe a linear scaling of the mixing efficiency with the Froude number and an increase of its value of roughly one order of magnitude.

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Section: Overturning Regions Vertical Draftsmentioning

confidence: 99%

Vertical drafts and mixing in stratified turbulence: Sharp transition with Froude number

Feraco¹,

Marino²,

Pumir³

et al. 2018

EPL

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“…These observations are being complemented with direct numerical simulations and large eddy simulations. The studies are particularly suitable for MLT cases, since they are characterized by high Reynolds numbers, that is,

scriptO false(1 0^{3} false)

(e.g., Fritts et al, ; Marino et al, ). For example, the comparison of KHIs from NLC observations with numerical simulations indicate a turbulent viscosity much larger (5 to 40 times) than the true kinematic viscosity at the NLC altitude (e.g., Fritts et al, ).…”

Section: Introductionmentioning

confidence: 99%

Four‐Dimensional Quantification of Kelvin‐Helmholtz Instabilities in the Polar Summer Mesosphere Using Volumetric Radar Imaging

Chau

Urco

Avsarkisov

et al. 2020

Geophysical Research Letters

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We present and characterize in time and three spatial dimensions a Kelvin‐Helmholtz Instability (KHI) event from polar mesospheric summer echoes (PMSE) observed with the Middle Atmosphere Alomar Radar System. We use a newly developed radar imaging mode, which observed PMSE intensity and line of sight velocity with high temporal and angular resolution. The identified KHI event occurs in a narrow layer of 2.4 km thickness centered at 85 km altitude, is elongated along north‐south direction, presents separation between billows of ∼8 km in the east‐west direction, and its billow width is ∼3 km. The accompanying vertical gradients of the horizontal wind are between 35 and 45 m/s/km and vertical velocities inside the billows are ±12 m/s. Based on the estimated Richardson ( <0.25), horizontal Froude ( ∼0.8), and buoyancy Reynolds ( ∼2.5 × 10 4 ) numbers, the observed event is a KHI that occurs under weak stratification and generates strong turbulence.

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“…IV. While extraction of waves and slow modes is often done using normal mode decompositions of the frozen in time fields in Fourier space [56,101,102], these approaches are based on linearized equations and thus can mix ageostrophic modes with balanced components of the flow. Better identification of balanced modes can be achieved using higher-order expansions of the equations [62].…”

Section: Spatio-temporal Spectrummentioning

confidence: 99%

Inverse cascades and resonant triads in rotating and stratified turbulence

et al. 2017

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Kraichnan seminal ideas on inverse cascades yielded new tools to study common phenomena in geophysical turbulent flows. In the atmosphere and the oceans, rotation and stratification result in a flow that can be approximated as two-dimensional at very large scales, but which requires considering three-dimensional effects to fully describe turbulent transport processes and non-linear phenomena. Motions can thus be classified into two classes: fast modes consisting of inertia-gravity waves, and slow quasi-geostrophic modes for which the Coriolis force and horizontal pressure gradients are close to balance. In this paper we review previous results on the strength of the inverse cascade in rotating and stratified flows, and then present new results on the effect of varying the strength of rotation and stratification (measured by the inverse Prandtl ratio N/f , of the Coriolis frequency to the Brunt-Väisäla frequency) on the amplitude of the waves and on the flow quasi-geostrophic behavior. We show that the inverse cascade is more efficient in the range of N/f for which resonant triads do not exist, 1/2 ≤ N/f ≤ 2. We then use the spatio-temporal spectrum to show that in this range slow modes dominate the dynamics, while the strength of the waves (and their relevance in the flow dynamics) is weaker.

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Interplay of waves and eddies in rotating stratified turbulence and the link with kinetic-potential energy partition

Cited by 40 publications

References 42 publications

Vertical drafts and mixing in stratified turbulence: Sharp transition with Froude number

Vertical drafts and mixing in stratified turbulence: Sharp transition with Froude number

Four‐Dimensional Quantification of Kelvin‐Helmholtz Instabilities in the Polar Summer Mesosphere Using Volumetric Radar Imaging

Inverse cascades and resonant triads in rotating and stratified turbulence

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