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| Titel |
Anisotropies of the Taylor Scale, Correlation Scale, and Effective Magnetic Reynolds Number Determination from Solar Wind Magnetic Field Fluctuations |
| VerfasserIn |
J. M. Weygand, M. G. Kivelson, M. H. Matthaeus, S. Dasso, L. M. Kistler |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028860
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| Zusammenfassung |
| ACE, Cluster, Geotail, IMP-8, Interball, THEMIS, and Wind data from many different
intervals in the solar wind are employed to determine the magnetic correlation scale and the
Taylor microscale from simultaneous multiple point measurements. For this study we define
the correlation scale as the exponential decay constant of the correlation coefficient as a
function of spacecraft separation and the Taylor scale as the radius of curvature of the
correlation coefficient values at zero separation. The present determination of the Taylor scale
makes use of a novel extrapolation technique to derive a statistically stable estimate from a
range of measurements at small spatial separations [Weygand et al., 2007]. Using all the slow
solar wind data (600 km/s), the correlation scale length is
found to be smallest (about 1.3x106 km) in the direction parallel to the magnetic
field and largest (about 2.2x106 km) in the direction perpendicular to the magnetic
field. The anisotropies in the turbulent magnetic fluctuations in the solar wind are
consistent with slow solar containing mainly two-dimensional turbulence and the fast
solar wind having mostly slab type turbulence. The effective magnetic Reynolds
number can be expressed in terms of the correlation scale and the Taylor scale. The
difference in the Taylor and correlation scale in the parallel and perpendicular direction
indicates that the effective magnetic Reynolds number varies with the direction
of the magnetic field and has values between 1x106 and 8x106 . Knowledge of
the effective magnetic Reynolds number may be useful in magnetohydrodynamic
modeling of the solar wind and galactic cosmic ray diffusion in the heliosphere. |
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