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Alfvén waves, alpha particles, and pickup ions in the solar wind
Author(s) -
Goldstein B. E.,
Neugebauer M.,
Smith E. J.
Publication year - 1995
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 - 10.1029/95gl03182
Subject(s) - physics , amplitude , solar wind , ecliptic , proton , phase velocity , anisotropy , computational physics , wave propagation , interplanetary medium , magnetic field , magnetohydrodynamics , plasma , astrophysics , optics , interplanetary spaceflight , nuclear physics , quantum mechanics
Past studies of the properties of Alfvén waves in the solar wind have indicated that (1) the amplitude of the velocity fluctuations is almost always smaller than expected on the basis of the amplitude of the field fluctuations, even when the anisotropy of the plasma is taken into account, and (2) the alpha particles often do not participate in the wave motions because they “surf” on the waves carried by the proton fluid. Ulysses data are used to demonstrate that (1) the discrepancy between the velocity and field fluctuations is greater at high heliographic latitudes than in the ecliptic plane, and (2) the alphas do participate in the waves, being either in phase or out of phase with the proton motions depending on whether the differential flow speed between the alphas and protons is greater than or less than the “observed” wave speed, V wave = δV B o /δB , as determined from the ratio of amplitudes of velocity and magnetic fluctuations. The possibility that the modification of Alfvén wave propagation speed is due to pressure anisotropies resulting from pickup ion distributions is investigated.