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Anisotropy and minimum variance directions of solar wind fluctuations in the outer heliosphereVoyager 2 magnetic field and plasma data are examined over time intervals of 1 to 12 hours in the heliospheric range of 1 to 10 AU to study the evolution of the anisotropy of solar wind fluctuations. Consistent with previous results, the directions of minimum variance vectors of magnetic fluctuations are found to be close to the mean magnetic field direction with an increasing component along the field at larger scales. At large radial distances there is more spread in the minimum variance directions than at smaller radial distances. The power in smaller-scale fluctuations in the magnetic field components perpendicular to the local mean field B(0) is in the ratio of about 5:1 near 1 AU at the scale of 1 hour but decreases to about 3:1 further out. No evidence for selective enhancement of out-of-the-ecliptic components of fluctuations is found. In contrast to results for field fluctuations, analysis of velocity fluctuations shows that the minimum variance direction systematically remains more radially oriented and becomes increasingly less oriented along B(0) with increasing heliocentric distance. The velocity fluctuations are generally more isotropic than the magnetic fluctuations. The observations cannot be explained by a superposed wave picture, and thus are consistent with the view that nonlinear turbulent evolution is responsible for the anisotropy in the fluctuations.
Document ID
19910043378
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Klein, Larry W.
(Applied Research Corp. Landover, MD, United States)
Roberts, D. Aaron
(Applied Research Corp. Landover, MD, United States)
Goldstein, Melvyn L.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 14, 2013
Publication Date
March 1, 1991
Publication Information
Publication: Journal of Geophysical Research
Volume: 96
ISSN: 0148-0227
Subject Category
Solar Physics
Accession Number
91A28001
Distribution Limits
Public
Copyright
Other

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