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Generation of Alfven‐ion cyclotron waves on auroral field lines in the presence of heavy ions
Author(s) -
Lysak Robert L.,
Temerin Michael A.
Publication year - 1983
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/gl010i008p00643
Subject(s) - physics , whistler , atomic physics , ion , cyclotron , electron , magnetic field , helium , electromagnetic radiation , field line , optics , nuclear physics , quantum mechanics
Observation of electromagnetic waves in the low‐altitude auroral zone at frequencies between the proton and helium gyrofrequencies suggests that Alfven‐ion cyclotron waves modified by the presence of helium ions are being excited. Estimates of the growth rates for this mode indicate that the auroral electron beam can provide the free energy for the instability. The effect of the heavy ions is to decrease the group velocity of the waves, leading to larger convective growth. Theoretical wave spectra are computed in the local approximation, which assumes that the gradient scale lengths in density and magnetic field are constant over the ray paths. Narrow banded spectral peaks similar to observations may be produced when the thickness of the electron beam is small (200 m at 3000 km altitude). Narrow beams also limit growth of whistler mode waves, which compete for the free energy of the electron beam.