A Parametric Study of Oxygen Ion Cyclotron Harmonic Wave Excitation and Polarization by an Oxygen Ring Distribution

Oxygen ion cyclotron harmonic (OCH) waves are electromagnetic emissions with frequencies near the harmonics of the oxygen ion cyclotron frequency. These waves can be excited by an energetic O+ ring distribution. Here, we perform a parametric study of OCH waves by an O+ ring distribution. We investigate the effects of ring concentration (eta(ho)), velocity (v(r)), temperature (T-r), total O+ concentration (eta(o)), and wave normal angles (WNAs) on the wave growth rate and polarization. We find that four-wave modes are related to OCH waves. The growth rates and frequency range increase with eta(ho) and eta(o) and decrease with T-r. The peak growth rate roughly follows the first peak of Jn2 ${J}_{n}<^>{2}$ (square of the Bessel function corresponding to the O+ ring) or cold plasma wave modes, which can be used to explain the v(r) and WNA dependences. OCH waves shift from the transverse mode to the compressional mode as v(r) increases.