Two modes of ion-ion hybrid waves in magnetospheric plasma

This paper is concerned with the structure of ion-ion hybrid (IIH) waves in multicomponent magnetospheric plasma in the dipole geomagnetic field model. Like Alfvén waves, in IIH waves the field line can oscillate in different directions: in the azimuthal direction (the toroidal modes) and in the radial direction (the poloidal modes). Contrary to Alfvén waves, in IIH waves only the equatorial part of the field line can oscillate, since due to the heavy ions admixture the IIH waves are trapped in the resonator in the vicinity of the geomagnetic equator. The equatorial localization of the waves allow the calculation of the parallel structure of the toroidal and poloidal IIH modes analytically. It was found that the toroidal and poloidal modes have slightly different structures and that their frequencies are also slightly different. The difference between toroidal and poloidal frequencies (the polarization splitting) is small with respect to the basic harmonics of each mode. It was found that IIH modes have a considerable compressional component of the wave's magnetic field.