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On the angle between the average interplanetary magnetic field and the propagation direction of plane large amplitude Alfvén waves
Author(s) -
Lichtenstein B. R.,
Sonett C. P.
Publication year - 1979
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl006i009p00713
Subject(s) - physics , amplitude , solar wind , magnetic field , computational physics , magnetohydrodynamics , interplanetary magnetic field , heliospheric current sheet , plane (geometry) , plane wave , field (mathematics) , geophysics , classical mechanics , geometry , optics , mathematics , quantum mechanics , pure mathematics
The direction of the time averaged magnetic field in a large amplitude Alfvén wave in the solar wind can be significantly different than the direction of the ambient interplanetary magnetic field which is not directly observable. The theoretical properties of plane large amplitude Alfvén waves in the MHD approximation constrain the time averaged magnetic field to cluster around the direction of minimum variance which is aligned with the wave normal . Thusspacecraft magnetometer observations in the solar wind of minimum variance directions strongly peaked about the average magnetic field directionparticularly in the leading edges of fast streamsare entirely consistent with plane large amplitude Alfvén waves which have wave normals aligned with the directions of minimum variance. These observations also do not necessarily imply that geometrical hydromagnetic calculations for Alfvén wave propagation direction in the solar wind are incorrect. Howeverthere is a discrepancy between geometrical hydromagnetics theory and observations that IMF minimum variance directions tend to be aligned with the ideal Parker spiral instead of the radial direction.