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| Titel |
Scaling laws of diffusion and time intermittency generated by coherent structures in atmospheric turbulence |
| VerfasserIn |
P. Paradisi, R. Cesari, A. Donateo, Daniele Contini, P. Allegrini |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 19, no. 1 ; Nr. 19, no. 1 (2012-02-15), S.113-126 |
| Datensatznummer |
250014168
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| Publikation (Nr.) |
 copernicus.org/npg-19-113-2012.pdf |
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| Zusammenfassung |
We investigate the time intermittency of turbulent transport
associated with the birth-death of self-organized coherent structures
in the atmospheric boundary layer.
We apply a threshold analysis on the increments of turbulent fluctuations
to extract sequences of rapid acceleration events, which is a
marker of the transition between self-organized structures.
The inter-event time distributions show a power-law
decay ψ(τ) ~ 1/τμ, with a strong
dependence of the power-law index μ on the threshold.
A recently developed method based on the application of event-driven walking rules to
generate different diffusion processes is applied to the experimental
event sequences.
At variance with the power-law index μ estimated from the inter-event
time distributions, the diffusion scaling H, defined by
⟨ X2⟩ ~ t2H, is independent from the threshold.
From the analysis of the diffusion scaling it can also be inferred
the presence of different kind of events, i.e. genuinely transition events
and spurious events, which all contribute to the diffusion process but over
different time scales.
The great advantage of event-driven diffusion lies in the ability of
separating different regimes of the scaling H. In fact, the greatest H,
corresponding to the most anomalous diffusion process, emerges in the long
time range, whereas the smallest H can be seen in the short time range if
the time resolution of the data is sufficiently accurate.
The estimated diffusion scaling is also robust under the change of the
definition of turbulent fluctuations and, under the assumption of
statistically independent events, it corresponds to a self-similar point
process with a well-defined power-law index μD ~ 2.1, where
D denotes that μD is
derived from the diffusion scaling.
We argue that this renewal point process can be associated to birth and death
of coherent structures and to
turbulent transport near the ground, where the contribution of turbulent
coherent structures becomes dominant. |
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