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| Titel |
Intermittency in MHD turbulence and coronal nanoflares modelling |
| VerfasserIn |
P. Veltri, G. Nigro, F. Malara, V. Carbone, A. Mangeney |
| 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 ; 12, no. 2 ; Nr. 12, no. 2 (2005-02-09), S.245-255 |
| Datensatznummer |
250010487
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| Publikation (Nr.) |
 copernicus.org/npg-12-245-2005.pdf |
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| Zusammenfassung |
| High resolution numerical simulations, solar wind data analysis, and measurements at
the edges of laboratory plasma devices have allowed for a huge progress in our
understanding of MHD turbulence. The high resolution of solar wind
measurements has allowed to characterize the intermittency observed at small scales.
We are now able to set up a consistent and convincing view of the main properties of
MHD turbulence, which in turn constitutes an extremely efficient tool in understanding
the behaviour of turbulent plasmas, like those in solar corona, where in situ observations are
not available. Using this knowledge a model to describe injection, due to foot-point
motions, storage and dissipation of MHD turbulence in coronal loops, is built where we assume
strong longitudinal magnetic field, low beta and high aspect ratio, which allows us to use the set
of reduced MHD equations (RMHD). The model is based on a shell technique in the wave
vector space orthogonal to the strong magnetic field, while the dependence on the longitudinal
coordinate is preserved. Numerical simulations show that injected energy is efficiently stored in the
loop where a significant level of magnetic and velocity fluctuations is obtained. Nonlinear interactions
give rise to an energy cascade towards smaller scales where energy is dissipated in an intermittent
fashion. Due to the strong longitudinal magnetic field, dissipative structures propagate along the loop,
with the typical speed of the Alfvén waves. The statistical analysis on the intermittent dissipative events
compares well with all observed properties of nanoflare emission statistics. Moreover the recent
observations of non thermal velocity measurements during flare occurrence are well described by the
numerical results of the simulation model. All these results naturally emerge from the model dynamical
evolution without any need of an ad-hoc hypothesis. |
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