Open AccessInteraction of propagating magnetosonic and Alfvén waves in a longitudinally inhomogeneous plasma
Author(s) -
Pilipenko V. A.,
Mazur N. G.,
Fedorov E. N.,
Engebretson M. J.
Publication year - 2008
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007ja012651
Subject(s) - physics , wkb approximation , monochromatic color , amplitude , field line , computational physics , plasma , wave propagation , alfvén wave , quantum electrodynamics , geophysics , magnetohydrodynamics , optics , quantum mechanics
The field line resonance theory has turned out to be very successful in the interpretation of the occurrence of narrow‐band ULF waves at middle and auroral latitudes. However, observational evidence has emerged (such as the occurrence of monochromatic Pc3 waves deep in the polar cap, Pi1B pulsations associated with tail plasma flows, and ULF waves in the magnetospheres of giant planets) which indicates that some basic assumptions of this theory may be insufficient in regions with open or very extended field lines. To interpret these observations, we suggest a model describing the interaction of propagating magnetosonic and Alfvén waves in longitudinally inhomogeneous plasma. A set of equations for the amplitudes of the interacting modes with account of finite frequency effect is obtained and investigated in the WKB approximation. In the synchronization region, where the wave vectors of the two modes approach one another, a substantial part of the fast magnetosonic wave energy is converted into the Alfvén wave energy. The phases of the waves are matched in such a way that the phase difference is most favorable for wave conversion. This conversion has a resonant character which may explain the occurrence of monochromatic waves with frequencies much higher than the field line eigenfrequency.