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Magnetic Helicity of Alfven Simple WavesThe magnetic helicity of fully nonlinear, multi-dimensional Alfven simple waves are investigated, by using relative helicity formulae and also by using an approach involving poloidal and toroidal decomposition of the magnetic field and magnetic vector potential. Different methods to calculate the magnetic vector potential are used, including the homotopy and Biot-Savart formulas. Two basic Alfven modes are identified: (a) the plane 1D Alfven simple wave given in standard texts, in which the Alfven wave propagates along the z-axis, with wave phase varphi=k_0(z-lambda t), where k_0 is the wave number and lambda is the group velocity of the wave, and (b)\ the generalized Barnes (1976) simple Alfven wave in which the wave normal {bf n} moves in a circle in the xy-plane perpendicular to the mean field, which is directed along the z-axis. The plane Alfven wave (a) is analogous to the slab Alfven mode and the generalized Barnes solution (b) is analogous to the 2D mode in Alfvenic, incompressible turbulence. The helicity characteristics of these two basic Alfven modes are distinct. The helicity characteristics of more general multi-dimensional simple Alfven waves are also investigated. Applications to nonlinear Aifvenic fluctuations and structures observed in the solar wind are discussed.
Document ID
20110006434
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Webb, Gary M.
(Alabama Univ. Huntsville, AL, United States)
Hu, Q.
(Alabama Univ. Huntsville, AL, United States)
Dasgupta, B.
(Alabama Univ. Huntsville, AL, United States)
Zank, G. P.
(Alabama Univ. Huntsville, AL, United States)
Roberts, D.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 25, 2013
Publication Date
November 15, 2010
Subject Category
Solar Physics
Meeting Information
Meeting: 2010 AGU (American Geophysical Union) Fall Meeting
Location: San Francisco, CA
Country: United States
Start Date: December 13, 2010
End Date: December 17, 2010
Distribution Limits
Public
Copyright
Other

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