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The Variance of Solar Wind Magnetic Fluctuations: Solutions and Further PuzzlesWe study the dependence of the variance directions of the magnetic field in the solar wind as a function of scale, radial distance, and Alfvenicity. The study resolves the question of why different studies have arrived at widely differing values for the maximum to minimum power (approximately equal to 3:1 up to approximately equal to 20:1). This is due to the decreasing anisotropy with increasing time interval chosen for the variance, and is a direct result of the "spherical polarization" of the waves which follows from the near constancy of |B|. The reason for the magnitude preserving evolution is still unresolved. Moreover, while the long-known tendency for the minimum variance to lie along the mean field also follows from this view (as shown by Barnes many years ago), there is no theory for why the minimum variance follows the field direction as the Parker angle changes. We show that this turning is quite generally true in Alfvenic regions over a wide range of heliocentric distances. The fact that nonAlfvenic regions, while still showing strong power anisotropies, tend to have a much broader range of angles between the minimum variance and the mean field makes it unlikely that the cause of the variance turning is to be found in a turbulence mechanism. There are no obvious alternative mechanisms, leaving us with another intriguing puzzle.
Document ID
20070032074
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Roberts, D. A.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Goldstein, M. L.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 23, 2013
Publication Date
December 11, 2006
Subject Category
Solar Physics
Meeting Information
Meeting: 2006 American Geophysical Union Fall Meeting
Location: San Francisco, CA
Country: United States
Start Date: December 11, 2006
End Date: December 15, 2006
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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