ENERGY-TRANSFER BETWEEN ENERGETIC RING CURRENT H-CYCLOTRON WAVES( ANDO+ BY ELECTROMAGNETIC ION)

Electromagnetic ion cyclotron (EMIC) waves in the frequency range belo w the helium gyrofrequency can be excited in the equatorial region of the outer magnetosphere by cyclotron resonant instability with anisotr opic ring current H+ ions. As the unducted waves propagate to higher l atitudes, the wave normal should become highly inclined to the ambient magnetic field. Under such conditions, wave energy can be absorbed by cyclotron resonant interactions with ambient O+, leading to ion heati ng perpendicular to the ambient magnetic field. Resonant wave absorpti on peaks in the vicinity of the bi-ion frequency and the second harmon ic of the O+ gyrofrequency. This absorption should mainly occur at lat itudes between 10 degrees and 30 degrees along auroral field lines (L greater than or equal to 7) in the postnoon sector. The concomitant io n heating perpendicular to the ambient magnetic field can contribute t o the isotropization and geomagnetic trapping of collapsed O+ ion coni cs (or beams) that originate from a low-altitude ionospheric source re gion. During geomagnetic storms when the O+ content of the magnetosphe re is significantly enhanced, the absorption of EMIC waves should beco me more efficient, and it may contribute to the observed acceleration of O+ ions of ionospheric origin up to ring current energies.