Observational Properties of Harmonic EMIC Waves: Statistical Study

Electromagnetic ion cyclotron (EMIC) waves are discrete electromagnetic emissions separated by multiple ion gyrofrequencies. Harmonic EMIC waves are defined as waves with a strong electric or magnetic field (or both) at the harmonics of the fundamental EMIC mode. In this paper, for the first time, we present a statistical study on harmonic EMIC waves by the Van Allen Probes. The EMIC waves are categorized into three types based on their harmonics: (a) Fundamental mode only (without higher harmonics), (b) electrostatic (ES) harmonics, and (c) electromagnetic (EM) harmonics. We find that most harmonic EMIC wave events are observed on the dayside, outside the plasmasphere and are associated with a low , a high proton , and a strong fundamental EMIC mode. ES harmonic EMIC waves tend to exhibit a larger ratio compared to EM harmonic EMIC waves. The results advance our understanding of harmonic EMIC waves and their generation mechanisms.