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Theory of scan plane flux anisotropiesWhen a spacecraft detector measures particle flux as a function of look direction in a plane (the scan plane), anisotropy is often seen. This anisotropy is caused by spatial gradients, by E x B particle drift, and by various spectral and geometric effects. This paper treats all of these effects systematically, starting from the nonrelativistic Vlasov equation. The general analysis is applied to a simple model of an anisotropic distribution to give a relation between the E x B drift, the gradient and the experimentally observed first, second, and third harmonics of the flux as a function of angle in the scan plane. Even with an assumed model, anisotropy observations in one plane alone do not suffice to determine the E x B drift velocity and the spatial gradient independently. If the E x B velocity is assumed (e.g., the corotational velocity in a rotating planetary magnetosphere), the spatial gradient may be deduced, and from it the time rate of change of flux in a nonrotating frame of reference.
Document ID
19810030252
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Northrop, T. G.
(NASA Goddard Space Flight Center Laboratory for High Energy Astrophysics, Greenbelt, Md., United States)
Thomsen, M. F.
(Iowa, University Iowa City, Iowa, United States)
Date Acquired
August 11, 2013
Publication Date
November 1, 1980
Publication Information
Publication: Journal of Geophysical Research
Volume: 85
Subject Category
Lunar And Planetary Exploration
Accession Number
81A14656
Funding Number(s)
CONTRACT_GRANT: NAS2-6553
Distribution Limits
Public
Copyright
Other

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