Relative Diffusion of Constant-Level Balloons in the Southern Hemisphere

Er-El, Joseph; Peskin, Richard L.

doi:10.1175/1520-0469(1981)038<2264:rdoclb>2.0.co;2

Cited by 54 publications

(42 citation statements)

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“…For the EOLE and TWERL atmospheric experiments, Morel & Larcheveque (1974) and Er-El & Peskin (1981) respectively give EKE ≈ 150 m 2 s −2 , R int ≈ O(1000) km (at mid-latitudes). Their observed value of τ ≈ 3 days is of the order of the predicted value τ ∼ 1.5 days.…”

Section: Discussionmentioning

confidence: 99%

“…In the TWERL experiment, Er El & Peskin (1981) confirmed this exponential regime but the demonstration of a Richardson regime at larger scale proved elusive. These authors emphasized the importance of looking at the dispersion in the time domain, a proposal that we share: we will show the differences that arise when averages of pair diffusivity are constructed as a function of distance or time.…”

Section: Introductionmentioning

confidence: 94%

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Open ocean regimes of relative dispersion

2005

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As two fluid particles separate in time, the entire spectrum of eddy motions is being sampled from the smallest to the largest scales. In large-scale geophysical systems for which the Earth rotation is important, it has been conjectured that the relative diffusivity should vary respectively as D 2 and D 4/3 for distances respectively smaller and larger than a well-defined forcing scale of the order of the internal Rossby radius (with D the r.m.s. separation distance). Particle paths data from a mid-latitude float experiment in the central part of the North Atlantic appear to support these statements partly: two particles initially separated by a few km within two distinct clusters west and east of the mid-Atlantic ridge, statistically dispersed following a Richardson regime (D 2 ∼ t 3 asymptotically) for r.m.s. separation distances between 40 and 300 km, in agreement with a D 4/3 law. At early times, and for smaller separation distances, an exponential growth, in agreement with a D 2 law, was briefly observed but only for the eastern cluster (with an e-folding time around 6 days). After a few months or separation distances greater than 300 km, the relative dispersion slowed down naturally to the Taylor absolute dispersion regime. IntroductionObservations of the separation of pairs of particles is one of the few experimental methods available to examine the spatial structure of geophysical turbulent flows. Richardson (1926) proposed that the relative diffusivity of an ensemble of pairs should scale as the 4/3 power of the (r.m.s.) separation distance. In his review of the subject, Corrsin (1962) emphasized the concept that turbulent eddies much smaller or much larger than the separation scale are relatively inefficient in further separation at the difference of eddies near the separation scale: the small eddies cause independent random walks of each member of the pair while the larger ones move the pair coherently as a single unit. As a result the relative velocity of the pair changes with the separation and is a non-stationary random variable. This accelerating property of relative diffusion has been used to infer properties of the energy wavenumber spectrum in the inertial range. The key quantity in the inertial range of three-dimensional turbulence is the energy dissipation rate. When the relative diffusivity is assumed to depend only on this energy dissipation rate and on separation, Richardson's law is recovered (Obukhov 1941;Batchelor 1952). The study of particle dispersion is important because of the interest in transport and mixing of chemicals in large-scale geophysical systems. While Taylor's (1921) single-particle dispersion theory relates to tracer dispersal from a fixed geographical origin and for very large times, two-particle dispersion relates to the spreading of a cloud of tracer from its centre of gravity (Batchelor 1952) and will

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 94%

Open ocean regimes of relative dispersion

2005

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“…The relative eddy diffusivity is expected to grow as the 4/3 power of the separation distance R(t), namely D(R) ≡ d R 2 (t) /dt ∼ R 4/3 , and the separation distance hence grows as R 2 (t) t 3 , as suggested by Richardson in his pioneering work (Richardson, 1926;Falkovich et al, 2001). Beyond the case of three-dimensional turbulence, the Richardson 4/3 law is observed also in the case of anisotropic relative dispersion, e.g.…”

Section: Introductionmentioning

confidence: 94%

“…LaCasce, 2010;Okubo, 1971;Morel and Larchevêque, 1974;Er-el and Peskin, 1981;Berti et al, 2011). This is only partly due to the inherent difficulties of performing float or dye concentration experiments in the ocean.…”

Section: Introductionmentioning

confidence: 99%

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Effects of vertical shear in modelling horizontal oceanic dispersion

et al. 2016

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Abstract. The effect of vertical shear on the horizontal dispersion properties of passive tracer particles on the continental shelf of the South Mediterranean is investigated by means of observation and model data. In situ current measurements reveal that vertical gradients of horizontal velocities in the upper mixing layer decorrelate quite fast ( ∼ 1 day), whereas an eddy-permitting ocean model, such as the Mediterranean Forecasting System, tends to overestimate such decorrelation time because of finite resolution effects. Horizontal dispersion, simulated by the Mediterranean sea Forecasting System, is mostly affected by: (1) unresolved scale motions, and mesoscale motions that are largely smoothed out at scales close to the grid spacing; (2) poorly resolved time variability in the profiles of the horizontal velocities in the upper layer. For the case study we have analysed, we show that a suitable use of deterministic kinematic parametrizations is helpful to implement realistic statistical features of tracer dispersion in two and three dimensions. The approach here suggested provides a functional tool to control the horizontal spreading of small organisms or substance concentrations, and is thus relevant for marine biology, pollutant dispersion as well as oil spill applications.

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Tropospheric dispersion: The first ten days after a puff release

Maryon

Buckland

1995

Quart J Royal Meteoro Soc

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Dispersion from a puff released in the atmospheric boundary layer in mid‐latitudes is simulated with a Lagrangian global multiple‐particle model using analysed three‐dimensional wind fields. Quantitative measures of the spread are computed and used to assess the influence of the synoptic system into which the puff is released, and the ways in which turbulent diffusion can contribute to the total spread. the nature of the dispersion over ten days is examined to elucidate the controlling meteorology and kinematics during the various phases which could be identified. the results are compared with measurements made from constant‐level balloons. A time index is proposed to characterize large‐scale dispersion from a point source.

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Relative Diffusion of Constant-Level Balloons in the Southern Hemisphere

Cited by 54 publications

References 0 publications

Open ocean regimes of relative dispersion

Open ocean regimes of relative dispersion

Effects of vertical shear in modelling horizontal oceanic dispersion

Tropospheric dispersion: The first ten days after a puff release

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