An expression for the linear electromagnetic ion cyclotron convective growth rate has been derived, considering multiple ions in the energetic anisotropic component of the plasma (which provides the free energy for the instability) as well as in the cold component of the plasma. This represents a modification of recent treatments investigating electromagnetic ion cyclotron growth rates which have considered only hydrogen ions in the energetic component. Four major effects on the growth and propagation characteristics result from inclusion of heavy ions in the energetic component. Some wave growth occurs at low frequencies below the corresponding marginally unstable wave mode for each heavy ion. Enhanced quasi-monochronomatic peaks in the convective growth rate appear just below the O + and He + gyrofrequency and can be quite pronounced for certain plasma conditions. Stop bands, decreased group velocity and other effects normally attributed to cold heavy ions can be produced or enhanced by heavy ions in the energetic plasma component. Partial or complete suppression of wave growth at frequencies above the marginally unstable wave mode for a particular energetic heavy ion can greatly alter the growth rates that would occur in the absence of this energetic heavy ion. The expression for the linear electromagnetic ion cyclotron convective growth rate along with appropriate plasma parameters was used to investigate the nature of linear wave growth in the plasmapause region. The frequencies of peaks in the convective growth rate given by this model compare favorably with wave measurements in this region. It is conceivable that through wave-particle interactions, electromagnetic ion cyclotron waves could supply the energy source for various plasmapause region phenomena such as the O + torus, the plasma cloak, and stable auroral red arcs. during varying amounts of geomagnetic activity. This is consistent with the theory of Cornwall et al. [ 1970]. Although the indirect evidence presented above and by other investigators is convincing, there still remains the problem of reconciling existing wave measurements with ion cyclotron wave theory. A possible explanation may result from our changing concept of the near plasmapause environment. The presence of heavy ions in the magnetospheric plasma has recently been discovered (e.g., Cornwall and Schultz [1979] and references therein). The plasma in this region consists of an energetic component (ring current plasma) and a cold component (plasmaspheric plasma), both of which contain heavy ions. The ring current is dominated by positive ions with energy _< 200 keV [Williams, 1983]. During the recovery phase of magnetic storms, the low-energy (0.2-17 keV) portion of the ring current at or below L values of 4 is composed mainly of O + and He + [Lundin et al., 1980]. Furthermore, there appears to be a marked composition boundary near L -4, with the heavy ions O + and He + dominating equatorward and with H + dominating poleward. This may be consistent with the much shorter lifetime of H...

We have systematically studied the effects that non‐Maxwellian ion velocity distributions produce on the ionic part of the spectrum of radar waves incoherently scattered from the disturbed high‐latitude ionosphere in the upper E and lower F regions. For ion to electron temperature ratios smaller than or equal to unity and electric field strengths greater than about 70 mV/m the spectrum is seriously distorted from the shape that it would normally have if the ion velocity distribution were Maxwellian. In events where the magnetospheric convection electric field exceeds 70 mV/m the interpretation of the data is affected if the erroneous assumption of a Maxwellian distribution is used to analyze the data. The electron temperature is the property most seriously affected by the erroneous interpretation, as it can be underestimated by as much as a factor of 2. Finally, the spectra obtained under disturbed conditions are anisotropic, the least distortions from a Maxwellian‐type spectrum being found along the magnetic field direction. The apparent ion temperature seen along the line of sight of the radar as it scans from parallel to the magnetic field to nearly perpendicular to the magnetic field also increases as the angle with the magnetic field increases, even for dc electric field strengths as small as 20 mV/m.

The effect of the finite thickness of the shear layer on the Kelvin-Helmholtz instability of the Earth's magnetopause boundary is investigated. The thickness of the layer stabilizes the boundary with respect to short wavelength perturbations, which were previously found to be unstable in the zero thickness analysis. Compressibility effects further stabilize the layer. The effects of the magnetic field on the instability are also discussed.

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