Visibility network analysis of large-scale intermittency in convective surface layer turbulence

Chowdhuri, Subharthi; Iacobello, Giovanni; Banerjee, Tirtha

doi:10.1017/jfm.2021.720

Cited by 13 publications

(13 citation statements)

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“…To avoid these problems, we undertake an alternate approach based on surrogate data. If there are two interrelated stochastic variables and they are randomly shuffled, then such a random shuffling operation should destroy any interrelationship between them (Chowdhuri et al ., 2021). Consequently, any possible dependencies between the higher‐order moments of the two stochastic variables, including the Pearson correlation coefficient, should cease to exist.…”

Section: Resultsmentioning

confidence: 99%

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A new methodology for the statistical descriptions of Particle‐by‐Particle measurements of liquid droplets in cumulus clouds

Bera

Chowdhuri

Prabha

2022

Quart J Royal Meteoro Soc

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Statistical and microphysical properties of liquid cloud droplets (with diameter 2-50 μm) in the growing stage of cumulus clouds are illustrated by in situ Particle-by-Particle (PbP) measurements. A contrasting statistical behaviour for the cloud core, following Poisson statistics with an indication of random spatial distribution, and the cloud edge which unveils non-Poisson statistics, tells of a heterogeneous spatial distribution. A new metric from the joint probability distribution function of droplet inter-arrival distance and droplet size is proposedfor quantifying the dynamics-microphysics interaction in cumulus clouds. We found that the interaction is stronger for the cloud edge compared to the undiluted core region. The scale dependency of mixing is studied using PbP data, and reveals a sharp change at length-scales below a critical value of around 40-60 cm, above which microphysical change of mixing is almost constant. This critical length-scale separates the mixing regimes between the homogeneous and inhomogeneous processes. Observation of such a critical length-scale of mixing from in situ measurements (at sub-metre scale) is the key finding of this study.

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Section: Resultsmentioning

confidence: 99%

“…The complementary CDFs are generally used when the behaviour in the tails of a distribution needs to be stressed (e.g. Chamecki, 2013; Chowdhuri et al ., 2021). For our case, it is quite evident from Figure 7a that the differences in the IPD distributions between the cloud‐core and ‐edge remain more pronounced at larger λ values (i.e.…”

Section: Resultsmentioning

confidence: 99%

A new methodology for the statistical descriptions of Particle‐by‐Particle measurements of liquid droplets in cumulus clouds

Bera

Chowdhuri

Prabha

2022

Quart J Royal Meteoro Soc

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“…To confirm whether this outcome is a consequence of coherent structures in canopy flows, we generate randomly shuffled surrogates of and signals and recompute . To briefly explain the shuffling procedure, one can select the time series of any signal and then operate a random permutation to disrupt the underlying temporal arrangement, thereby creating a surrogate dataset that does not possess any relationship among the signal data points (Chowdhuri, Iacobello & Banerjee 2021). In this process, the signal's p.d.f.…”

Section: Resultsmentioning

confidence: 99%

“…This is a standard procedure while comparing any two statistical distributions (Chowdhuri et al. 2021). Mathematically, such an operation can be expressed as where the functions indicate the cumulative flux distributions at a particular scale and is the absolute difference between the original () and surrogate () datasets at that scale.…”

Section: Resultsmentioning

confidence: 99%

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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“…The family of visibility algorithms as graph-theoretic methods for time series were first proposed in [30,31] and since then they have been successfully applied to a range of problems in many scientific disciplines, from purely theoretical analysis [35][36][37], description of nonlinear [38][39][40] and stochastic dynamics [41,42] to applications in physical [43][44][45][46][47], biological [48][49][50] and socio-technical systems [51][52][53][54], even in the arts [55] (see [56,57] for reviews on graph-theoretic methods for signal processing). The methods offer simple and computationally efficient mappings between an ordered sequence -i.e.…”

Section: A Experimental Setup and Data Collectionmentioning

confidence: 99%