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| Titel |
Turbulence and Self- Organised Criticality under finite driving- how they can look the same, and how they are different. |
| VerfasserIn |
S. Rosenberg, S. C. Chapman, N. W. Watkins |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033004
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| Zusammenfassung |
| The paradigm of Self- Organised Criticality (SOC) has found application in understanding
scaling and bursty transport in driven, dissipative plasmas such as at the earth’s
magnetosphere and the solar corona. Turbulence also has scaling and bursty transport as its
observable signature so that the question naturally arises as to if, or how, these phenomena
are related. SOC a limiting process that occurs as the ratio of driving rate to dissipation rate is
taken to zero, while idealized turbulence takes this ratio to infinity. We consider the more
realistic scenario of finite driving rate. We demonstrate the difficulty of distinguishing SOC
and turbulence under these conditions with a simple multifractal test timeseries, the p- model-
which we show both exhibits multifractal scaling in its structure functions and power
law avalanche statistics. We use similarity analysis (Buckingham’s Î theorem) to
identify the control parameter RA which is analogous to the Reynolds Number
RE of turbulence in that it relates to the number of excited degrees of freedom,
that is, the range of spatio-temporal scales over which one finds scaling behaviour.
However for avalanching systems the number of excited degrees of freedom is
maximal at the zero driving rate, SOC limit, in the opposite sense to fluid turbulence.
Practically, at finite RE or RA one observes scaling over a finite range which for
turbulence, increases with RE and for SOC, decreases with RA, suggesting an observable
trend to distinguish them. We use the BTW sandpile model to explore this idea
and find that whilst avalanche distributions can, depending on the details of the
driving, reflect this behaviour, power spectra are not clear discriminators of an SOC
state. |
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