The authors investigate atmospheric internal gravity waves (IGWs): their generation and induction of global intermittent turbulence in the nocturnal stable atmospheric boundary layer based on the new concept of turbulence generation discussed in a prior paper by Sun et al. The IGWs are generated by air lifted by convergence forced by the colliding background flow and cold currents near the ground. The buoyancy-forced IGWs enhance wind speed at the wind speed wave crests such that the bulk shear instability generates large coherent eddies, which augment local turbulent mixing and vertically redistribute momentum and heat. The periodically enhanced turbulent mixing, in turn, modifies the air temperature and flow oscillations of the original IGWs. These turbulence-forced oscillations (TFOs) resemble waves and coherently transport momentum and sensible heat. The observed momentum and sensible heat fluxes at the IGW frequency, which are due to either the buoyancy-forced IGWs themselves or the TFOs, are...

Wind and Temperature Oscillations Generated by Wave-Turbulence Interactions in the Stably Stratified Boundary Layer

Abstract The presence of waves is proven to be ubiquitous within nocturnal stable boundary layers over complex terrain, where turbulence is in a continuous, although weak, state of activity. The typical approach based on Reynolds decomposition is unable to disaggregate waves from turbulence contributions, thus hiding any information about the production/destruction of turbulence energy injected/subtracted by the wave motion. We adopt a triple-decomposition approach to disaggregate the mean, wave, and turbulence contributions within near-surface boundary-layer flows, with the aim of unveiling the role of wave motion as a source and/or sink of turbulence kinetic and potential energies in the respective explicit budgets. By exploring the balance between buoyancy (driving waves) and shear (driving turbulence), a simple interpretation paradigm is introduced to distinguish two layers, namely the near-ground and far-ground sublayer, estimating where the turbulence kinetic energy can significantly feed or be fed by the wave. To prove this paradigm, a nocturnal valley flow is used as a case study to detail the role of wave motions on the kinetic and potential energy budgets within the two sublayers. From this dataset, the explicit kinetic and potential energy budgets are calculated, relying on a variance–covariance analysis to further comprehend the balance of energy production/destruction in each sublayer. With this investigation, we propose a simple interpretation scheme to capture and interpret the extent of the complex interaction between waves and turbulence in nocturnal stable boundary layers. 

/pdf/interaction-between-waves-and-turbulence-within-the-sn2trezs.pdf

Interaction Between Waves and Turbulence Within the Nocturnal Boundary Layer

Abstract Direct numerical simulations of turbulent flow in a channel with one rigid and one viscoelastic wall are performed. An Eulerian–Eulerian model is adopted with a level-set approach to identify the fluid–compliant material interface. Focus is placed on the propagation of Rayleigh waves in the compliant material, whose speed depends on the shear modulus of elasticity and whose dominant wavelength depends on the thickness of the viscoelastic layer. These parameters are selected to ensure coupling between the compliant surface and turbulence. When the phase speed of Rayleigh waves is commensurate with the advection velocity of near-wall pressure fluctuations, sheets of vorticity are lifted up and detached near the critical layer and lead to a local pressure minimum. These events are caused by the inflectional velocity profile near the troughs, and are controlled by the net vorticity flux at the elastic surface. This phenomenon is central to understanding the statistical characteristics of the flow, including the surface deformation–pressure correlation and enhanced stochastic Reynolds shear stresses. Finally, we discuss the influence of three-dimensionality of the surface topography on the generation of streamwise vorticity, secondary motions and lateral turbulent transport.

Spatiotemporal characterization of turbulent channel flow with a hyperelastic compliant wall

The dynamics across different scales in the stable atmospheric boundary layer has been investigated by means of two metrics, based on instantaneous fractal dimensions and grounded in dynamical systems theory. The wind velocity fluctuations obtained from data collected during the Cooperative Atmosphere-Surface Exchange Study-1999 experiment were analyzed to provide a local (in terms of scales) and an instantaneous (in terms of time) description of the fractal properties and predictability of the system. By analyzing the phase-space projections of the continuous turbulent, intermittent, and radiative regimes, a progressive transformation, characterized by the emergence of multiple low-dimensional clusters embedded in a high-dimensional shell and a two-lobe mirror symmetrical structure of the inverse persistence, have been found. The phase space becomes increasingly complex and anisotropic as the turbulent fluctuations become uncorrelated. The phase space is characterized by a three-dimensional structure for the continuous turbulent samples in a range of scales compatible with the inertial subrange, where the phase-space-filling turbulent fluctuations dominate the dynamics, and is low dimensional in the other regimes. Moreover, lower-dimensional structures present a stronger persistence than the higher-dimensional structures. Eventually, all samples recover a three-dimensional structure and higher persistence level at large scales, far from the inertial subrange. The two metrics obtained in the analysis can be considered as proxies for the decorrelation time and the local anisotropy in the turbulent flow.

https://hal.science/hal-03879836/document

Local dimensionality and inverse persistence analysis of atmospheric turbulence in the stable boundary layer.

On the parametrizations for the dissipation rate of the turbulence kinetic energy in stable conditions

In the realm of boundary-layer flows in complex terrain, low-level jets (LLJs) have received considerable attention, although little literature is available for double-nosed LLJs that remain not well understood. To this end, we use the MATERHORN dataset to demonstrate that double-nosed LLJs developing within the planetary boundary layer (PBL) are common during stable nocturnal conditions and present two possible mechanisms responsible for their formation. It is observed that the onset of a double-nosed LLJ is associated with a temporary shape modification of an already-established LLJ. The characteristics of these double-nosed LLJs are described using a refined version of identification criteria proposed in the literature, and their formation is classified in terms of two driving mechanisms. The wind-driven mechanism encompasses cases where the two noses are associated with different air masses flowing one on top of the other. The wave-driven mechanism involves the vertical momentum transport by an inertial-gravity wave to generate the second nose. The wave-driven mechanism is corroborated by the analysis of nocturnal double-nosed LLJs, where inertial-gravity waves are generated close to the ground by a sudden flow perturbation.

Luigi Brogno

Papers

Interaction Between Waves and Turbulence Within the Nocturnal Boundary Layer

Driving Mechanisms of Double-Nosed Low-Level Jets during MATERHORN Experiment

On the parametrizations for the dissipation rate of the turbulence kinetic energy in stable conditions