The gyroresonant interaction between electromagnetic ion cyclotron (EMIC) wavesand energetic particles was studied in a multi-ion (H^+, He^+, and O^+) plasma. The minimumresonant energy E_min, resonant wave frequency ω, and pitch angle diffusion coefficient D_(αα) werecalculated at the center location of the symmetrical ring current: r 3.5R_E with R_E the Earth'sradius. E_(min) is found to decrease rapidly from 10 MeV to a few keV with the increase in ω in threebands: H^+-band, He^+-band and O^+-band. Moreover, EMIC waves have substantial potential toscatter energetic (～100 keV) ions (mainly H^+ and He^+) into the loss cone and yield precipitationloss, suggesting that wave-particle interactions contribute to ring current decay.
A three-dimensional ray tracing study of a whistler-mode chorus is conducted fordifferent geomagnetic activities by using a global core plasma density model.For the upperbandchorus,the initial azimuthal wave angle affects slightly the projection of ray trajectoriesonto the plane(Z,（（x2+y2））1/2),but controls the longitudinal propagation.The trajectory ofthe upper-band chorus is strongly associated with the plasmapause and the magnetic local time（MLT）of chorus source region.For the high geomagnetic activity,the chorus trajectory movesinward together with the plasmapause.In the bulge region,the plasmapause extends outward,while the chorus trajectory moves outward together with the plasmapause.For moderately orhigh geomagnetic activity,the lower-band chorus suffers low hybrid resonance（LHR）reflectionbefore it reaches the plasmapause,leading to a weak correlation with the geomagnetic activityand magnetic local time of the chorus source region.For low geomagnetic activity,the lower-bandchorus may be reflected firstly at the plasmapause instead of suffering LHR reflection,exhibitinga propagation characteristic similar to that of the upper-band chorus.The results provide a newinsight into the propagation characteristics of the chorus for different geomagnetic activities andcontribute to further understanding of the acceleration of energetic electron by a chorus wave.
