Parallel structure of Pc1 ULF oscillations in multi-ion magnetospheric plasma at finite ion gyrofrequency

The paper deals with the spatial structure of the Pc1 oscillations in multicomponent (protons and heavy ions) space plasma. As earlier studies (Guglielmi et al., 2000 and Guglielmi et al., 2001 and others) showed, an inhomogeneity along magnetic field and a finite ion gyrofrequency cause the formation in the equatorial region, a resonator which serves as a wave energy reservoir and determines the wave frequency. The present paper represents an extension of these ideas to the case of quasi-perpendicular wave propagation, k⊥⪢k∥k⊥⪢k∥. It is shown that the resonator eigenfrequencies are very close to each other, which can result in formation of beating resembling the Pc1 pearl structure. On each side of the resonator there is an opaque region bounded by a parallel singular point, and a transparent region between this point and the ionosphere. At the parallel singular point the wave amplitude is finite. Compared to the case k⊥⪡k∥k⊥⪡k∥ studied by Guglielmi et al., this resonator has a lower frequency and is a bit more narrow, and the near-ionospheric transparent region is wider, although on the order of the magnitude the parameters of the mode parallel structure in these two cases coincide.

Research Highlights
► Admixture of heavy ions prevents propagation of the short-period quasi-perpendicular Alfven wave along the whole field line.
► The parallel resonator in the equatorial region is formed.
► A near-ionospheric transparent region along the field line is formed, bounded by a singular point.
► The equatorial resonator and the near-ionospheric transparent region are separated by opaque regions.