EMIC Waves Converted From Equatorial Noise Due to M/Q = 2 Ions in the Plasmasphere: Observations From Van Allen Probes and Arase

Abstract

Equatorial noise (EN) emissions are observed inside and outside the plasmapause. EN emissions are referred to as magnetosonic mode waves. Using data from Van Allen Probes and Arase, we found conversion from EN emissions to electromagnetic ion cyclotron (EMIC) waves in the plasmasphere and in the topside ionosphere. A low‐frequency part of EN emissions becomes EMIC waves through branch splitting of EN emissions, and the mode conversion from EN to EMIC waves occurs around the frequency of M/Q = 2 (deuteron and/or alpha particles) cyclotron frequency. These processes result in plasmaspheric EMIC waves. We investigated the ion composition ratio by characteristic frequencies of EN emissions and EMIC waves and obtained ion composition ratios. We found that the maximum composition ratio of M/Q = 2 ions is ~10% below 3,000 km. The quantitative estimation of the ion composition will contribute to improving the plasma model of the deep plasmasphere and the topside ionosphere.

Oxygen torus and its coincidence with EMIC wave in the deep inner magnetosphere: Van Allen Probe B and Arase observations

“…However, the EMIC waves in the oxygen torus provide us a clue to estimate the ion composition more precisely. The similar approach has been applied for EMIC waves and equatorial noise emissions observed by Arase (Miyoshi et al 2019 ). From Fig.…”

The First Observation of N+ Electromagnetic Ion Cyclotron Waves

“…However, linearly polarized, small wave normal angles, N + EMIC waves observed at low L-shells can be generated via the mode conversion of compressional waves at the ion-ion hybrid/Buchsbaum resonance (Lee et al, 2008;Kim et al, 2015Kim et al, , 2019, and/or due to the free energy from ring velocity distribution of ring current protons ( However, this first observation of N + EMIC wave provides evidence of the N + ions presence in the near-Earth region, in addition to O + , during this event. This study opens up the new avenues of quantifying the relative concentrations of N + and O + based on EMIC wave observations from current missions (e.g., Van Allen Probes, MMS, and Cluster), which can be used as a tool to infer the N + ion concentration using the observed characteristic frequencies (Kim et al, 2015;Min et al, 2015;Miyoshi et al, 2019). Inferred N + ion concentration can reveal N + torus and N + warm plasma cloak by quantifying O + torus (Nosé et al, 2018(Nosé et al, , 2020(Nosé et al, , 2015(Nosé et al, , 2011 and O + warm plasma cloak (Chappell et al, 2008).…”

Equatorial F‐Region Plasma Waves and Instabilities Observed Near Midnight at Solar Minimum During the NASA Too WINDY Sounding Rocket Experiment

“…In those observations, the hiss vanished in regions where low-frequency electric fields associated with plasma density irregularities characteristic of spread F conditions were present. Miyoshi et al (2019) presented observations of equatorial noise emissions in the topside ionosphere made with the Van Allen probes. They associated gaps in the spectra at ion gyroharmonic frequencies with mode conversion to electromagnetic ion cyclotron (EMIC) waves.…”