Velocity and Temperature Dissimilarity in the Surface Layer Uncovered by the Telegraph Approximation

Huang, Kelly Y.; Katul, Gabriel G.; Hultmark, Marcus

doi:10.1007/s10546-021-00632-2

Cited by 9 publications

(10 citation statements)

References 52 publications

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“…Figure 5 demonstrates how these attributes of the isosurface geometry and their crossing properties propagate to structure function statistics. The same trends in the transition to the production range are also apparent from the spectrum of a TA signal (Huang, Katul & Hultmark 2021), likely due to the TA signal exhibiting the same exponential cutoff in figure 3 imposed by the larger-scale geometries.…”

Section: Resultssupporting

confidence: 54%

Self-similar geometries within the inertial subrange of scales in boundary layer turbulence

et al. 2022

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The inertial subrange of turbulent scales is commonly reflected by a power law signature in ensemble statistics such as the energy spectrum and structure functions – both in theory and from observations. Despite promising findings on the topic of fractal geometries in turbulence, there is no accepted image for the physical flow features corresponding to this statistical signature in the inertial subrange. The present study uses boundary layer turbulence measurements to evaluate the self-similar geometric properties of velocity isosurfaces and investigate their influence on statistics for the velocity signal. The fractal dimension of streamwise velocity isosurfaces, indicating statistical self-similarity in the size of ‘wrinkles’ along each isosurface, is shown to be constant only within the inertial subrange of scales. For the transition between the inertial subrange and production range, it is inferred that the largest wrinkles become increasingly confined by the overall size of large-scale coherent velocity regions such as uniform momentum zones. The self-similarity of isosurfaces yields power-law trends in subsequent one-dimensional statistics. For instance, the theoretical 2/3 power-law exponent for the structure function can be recovered by considering the collective behaviour of numerous isosurface level sets. The results suggest that the physical presence of inertial subrange eddies is manifested in the self-similar wrinkles of isosurfaces.

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Section: Resultssupporting

confidence: 54%

Self-similar geometries within the inertial subrange of scales in boundary layer turbulence

et al. 2022

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“…2012; Chowdhuri et al. 2020 a ; Huang, Katul & Hultmark 2021). Therefore, it is prudent to use the values of and for renormalizing the persistence time scales, .…”

Section: Resultsmentioning

confidence: 99%

“…First, the use of Γ x allows one to judge whether the t p values are smaller or larger than the inertial subrange, since the scales smaller than Γ x are generally associated with such behaviours (Kaimal & Finnigan 1994;Manshour et al 2016). Second, the power-law exponents of the persistence p.d.f.s are typically explained in a framework of self-organized criticality and connected with the spectral slope in the inertial subrange, subjected to corrections accounting for small-scale intermittency (Cava et al 2012;Chowdhuri et al 2020a;Huang, Katul & Hultmark 2021). Therefore, it is prudent to use the values of Γ u and Γ w for renormalizing the persistence time scales, t p .…”

Section: Persistence Pdfs Of Velocity Fluctuationsmentioning

confidence: 99%

“…They mentioned that the length scales obtained from their event-based analysis could indeed be related to the spectrum of wall shear stress, thereby implying that such scales were the carriers of the Reynolds-stress fluctuations. Moreover, in the context of atmospheric turbulence, Huang et al (2021) presented an analogy between the turbulence spectra and the shape of persistence p.d.f.s. Therefore, from this perspective, the fact that persistence time scales smaller than Γ w hardly contribute to the momentum is in qualitative agreement with the assumption of quasi-isotropic conditions in inertial-subrange turbulence (Wyngaard & Coté 1972).…”

Section: Short-and Long-lived Eventsmentioning

confidence: 99%

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A scale-wise analysis of intermittent momentum transport in dense canopy flows

2022

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We investigate the intermittent dynamics of momentum transport and its underlying time scales in the near-wall region of the neutrally stratified atmospheric boundary layer in the presence of a vegetation canopy. This is achieved through an empirical analysis of the persistence time scales (periods between successive zero-crossings) of momentum flux events, and their connection to the ejection–sweep cycle. Using high-frequency measurements from the GoAmazon campaign, spanning multiple heights within and above a dense canopy, the analysis suggests that, when the persistence time scales ( $t_p$ ) of momentum flux events from four different quadrants are separately normalized by $\varGamma _{w}$ (integral time scale of the vertical velocity), their distributions $P(t_p/\varGamma _{w})$ remain height-invariant. This result points to a persistent memory imposed by canopy-induced coherent structures, and to their role as an efficient momentum-transporting mechanism between the canopy airspace and the region immediately above. Moreover, $P(t_p/\varGamma _{w})$ exhibits a power-law scaling at times $t_{p}<\varGamma _{w}$ , with an exponential tail appearing for $t_{p} \geq \varGamma _{w}$ . By separating the flux events based on $t_p$ , we discover that around 80 % of the momentum is transported through the long-lived events ( $t_{p} \geq \varGamma _{w}$ ) at heights immediately above the canopy, while the short-lived ones ( $t_{p} < \varGamma _{w}$ ) only contribute marginally ( $\approx 20\,\%$ ). To explain the role of instantaneous flux amplitudes in momentum transport, we compare the measurements with newly developed surrogate data and establish that the range of time scales involved with amplitude variations in the fluxes tends to increase as one transitions from within to above the canopy.

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“…We also analyze the temporal intermittency and clustering tendencies of the whitecap coverage with the telegraph approximation (TA), a methodology that isolates the time variability of a time series from its amplitude variations. The TA formalism has previously been used to uncover similarity structures in other intermittent stochastic processes such as turbulent velocity and temperature fluctuations (Cava et al, 2012;Huang et al, 2021;Sreenivasan & Bershadskii, 2006). However, to our knowledge this is the first application of the TA to the study of the intermittency of wave breaking.…”

Section: Plain Language Summarymentioning

confidence: 99%

On the Groupiness and Intermittency of Oceanic Whitecaps

et al. 2022

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The enhancement of wave breaking activity during wave group passage is investigated using coherent field observations of the instantaneous sea surface elevation and whitecap coverage from platform‐based stereo video measurements in the central North Sea. Passing wave groups are shown to be associated with a two to threefold enhancement in the probability distribution of total whitecap coverage W whereas the enhancement of active whitecap coverage WA is approximately fivefold. Breaking time scales and intermittency characteristics are also investigated with the inclusion of a secondary data set of W and WA observations collected during a research cruise in the North Pacific. The time scale analysis suggests a universal periodicity in wave breaking activity within a representative sea‐surface area encompassing approximately one dominant wave crest. The breaking periodicity is shown to be closely linked to the peak period of the dominant wave components, suggesting that long‐wave modulation of wave breaking is a predominant mechanism controlling the intermittency of wave breaking across scales.

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Velocity and Temperature Dissimilarity in the Surface Layer Uncovered by the Telegraph Approximation

Cited by 9 publications

References 52 publications

Self-similar geometries within the inertial subrange of scales in boundary layer turbulence

Self-similar geometries within the inertial subrange of scales in boundary layer turbulence

A scale-wise analysis of intermittent momentum transport in dense canopy flows

On the Groupiness and Intermittency of Oceanic Whitecaps

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