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| Titel |
An extended structure-function model and its application to the analysis of solar wind intermittency properties |
| VerfasserIn |
C.-Y. Tu, E. Marsch, H. Rosenbauer |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 14, no. 3 ; Nr. 14, no. 3, S.270-285 |
| Datensatznummer |
250012206
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| Publikation (Nr.) |
 copernicus.org/angeo-14-270-1996.pdf |
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| Zusammenfassung |
| An extended structure-function model is
developed by including the new effect in the p-model of Meneveau and
Sreenivasan which shows that the averaged energy cascade rate changes with
scale, a situation which has been found to prevail in non-fully-developed
turbulence in the inner solar wind. This model is useful for the small-scale
fluctuations in the inner heliosphere, where the turbulence is not fully
developed and cannot be explained quantitatively by any of the previous
intermittency turbulence models. With two model parameters, the intrinsic index
of the energy spectrum α, and the fragmentation fraction P1,
the model can fit, for the first time, all the observed scaling exponents of the
structure functions, which are calculated for time lags ranging from 81 s to 0.7
h from the Helios solar wind data. From the cases we studied we cannot establish
for P1 either a clear radial evolution trend, or a
solar-wind-speed or stream-structure dependence or a systematic anisotropy for
both the flow velocity and magnetic field component fluctuations. Generally, P1
has values between 0.7 and 0.8. However, in some cases in low-speed wind P1
has somewhat higher values for the magnetic components, especially for the
radial component. In high-speed wind, the inferred intrinsic spectral indices
α of the velocity and magnetic field components are about equal,
while the experimental spectral indices derived from the observed power spectra
differ. The magnetic index is somewhat larger than the index of the velocity
spectrum. For magnetic fluctuations in both high- and low-speed winds, the
intrinsic exponent α has values which are near 1.5, while the
observed spectral exponent has much higher values. In the solar wind with
considerable density fluctuations near the interplanetary current sheet near 1
AU, it is found that P1 has a comparatively high value of 0.89
for Vx . The impact of these results on the understanding of
the nature of solar wind fluctuations is discussed, and the limitations in using
structure functions to study intermittency are also described. |
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