Premium
Effects of azimuthal asymmetry on ULF waves in the dipole magnetosphere
Author(s) -
Lee DongHun,
Lysak Robert L.
Publication year - 1990
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/gl017i001p00053
Subject(s) - physics , magnetosphere , azimuth , wavenumber , dipole , wavelength , computational physics , wave propagation , longitudinal wave , magnetopause , asymmetry , geophysics , quantum electrodynamics , magnetic field , optics , quantum mechanics
The properties of the coupling of compressional and transverse ULF waves strongly depend on the azimuthal wavenumber m . We investigate these effects in a numerical model of ULF wave propagation in a dipolar magnetosphere. As the azimuthal wave number m becomes larger, the frequencies of the global modes are increased, each coupling location is shifted toward the plasmapause, and the wave energy of global compressional modes in the magnetosphere is confined to a smaller region near the magnetopause. These conclusions are qualitatively consistent with previous analytical and numerical models. It is suggested that the radial dependence of the azimuthal wavelength in the dipole geometry is important to the propagation of compressional waves. This effect is not present in either box or cylindrical models, in which the azimuthal wavelength does not depend on the radial distance, and can be distinguished from effects arising from the inhomogeneity of the Alfven speed. On the other hand, the Alfven shear modes are found to have periods independent of m .