5:15 PM - 7:15 PM
[PEM13-P04] EMIC Waves in the Magnetosphere: Attempts to Derive Ion Composition Using Polarization Analysis by the Arase Satellite
Keywords:Earth, Arase, magnetosphere, EMIC waves, ion composition
Electromagnetic ion cyclotron (EMIC) waves are low-frequency, circularly polarized electromagnetic waves excited by anisotropic ion distributions. These waves exhibit frequency and polarization characteristics which depend on each ion’s cyclotron frequency and the density of each ion species. Thus, if the wave is sufficiently intense and has broad bandwidth, it is potentially possible to estimate the ion composition of the surrounding plasma. Particle instruments onboard satellites often struggle to detect low-energy ions below 10-20 eV. Therefore, investigating EMIC waves enables the inference of ion species and their compositions, providing insights into magnetospheric dynamics.
Previous observations by the Akebono satellite and Van Allen Probes (VAP) have identified EMIC waves, as well as mode conversion events that are useful for estimating ion composition [Matsuda et al., 2015; Miyoshi et al. 2019]. However, only one mode conversion event has been reported by the Arase satellite [Miyoshi et al., 2019, Fig.2], and ion compositions have not been extensively discussed. This study aims to investigate EMIC waves more comprehensively using magnetic field data from the Arase satellite and to determine the distribution and dynamics of cold ion compositions from the topside ionosphere to the plasmasphere.
In this study, we use 256 Hz triaxial magnetic field data from Magnetic Field Experiment (MGF) [Matsuoka et al., 2018] (collected continuously near the Earth since 2017), and 1,024 Hz waveform data from Wave Form Capture (WFC) [Matsuda et al., 2018] (EMIC-Burst data: obtained intermittently from March 2017 to October 2018, during periods when triaxial magnetic field waveform data from the search coil were available) onboard the Arase satellite. As of February 2025, we are searching for “EMIC waves with sufficient intensity and broad frequency coverage across H+, He+, O+ cyclotron frequencies”, which could allow us to derive ion composition. For these events, we apply analysis methods previously used for Akebono and VAP to estimate ion composition. We perform polarization analysis with the singular value decomposition (SVD) method [Santolik et al., 2003] to determine polarization properties, wave normal angle (WNA), which indicates the propagation direction, and planarity. Then, we derive ion compositions by identifying cutoff frequencies and crossover frequencies, which provide information on the ambient ion composition.
In this presentation, we will report the initial results of our analysis using MGF data since 2017 and WFC (EMIC-Burst) from March 2017 to October 2018.
This study primarily aims to examine ion compositions and their temporal variations in the Earth’s magnetosphere using EMIC waves. However, the methodology can also be applied to other planetary magnetospheres with intrinsic magnetic fields. For instance, this approach could be extended to analyze magnetic field data from BepiColombo, which is expected to arrive at Mercury in November 2026. Observations in the Jovian system are no exception: Juno has conducted several flybys at the Galilean moons, and JUICE is expected to orbit Jupiter from 2031.
Previous observations by the Akebono satellite and Van Allen Probes (VAP) have identified EMIC waves, as well as mode conversion events that are useful for estimating ion composition [Matsuda et al., 2015; Miyoshi et al. 2019]. However, only one mode conversion event has been reported by the Arase satellite [Miyoshi et al., 2019, Fig.2], and ion compositions have not been extensively discussed. This study aims to investigate EMIC waves more comprehensively using magnetic field data from the Arase satellite and to determine the distribution and dynamics of cold ion compositions from the topside ionosphere to the plasmasphere.
In this study, we use 256 Hz triaxial magnetic field data from Magnetic Field Experiment (MGF) [Matsuoka et al., 2018] (collected continuously near the Earth since 2017), and 1,024 Hz waveform data from Wave Form Capture (WFC) [Matsuda et al., 2018] (EMIC-Burst data: obtained intermittently from March 2017 to October 2018, during periods when triaxial magnetic field waveform data from the search coil were available) onboard the Arase satellite. As of February 2025, we are searching for “EMIC waves with sufficient intensity and broad frequency coverage across H+, He+, O+ cyclotron frequencies”, which could allow us to derive ion composition. For these events, we apply analysis methods previously used for Akebono and VAP to estimate ion composition. We perform polarization analysis with the singular value decomposition (SVD) method [Santolik et al., 2003] to determine polarization properties, wave normal angle (WNA), which indicates the propagation direction, and planarity. Then, we derive ion compositions by identifying cutoff frequencies and crossover frequencies, which provide information on the ambient ion composition.
In this presentation, we will report the initial results of our analysis using MGF data since 2017 and WFC (EMIC-Burst) from March 2017 to October 2018.
This study primarily aims to examine ion compositions and their temporal variations in the Earth’s magnetosphere using EMIC waves. However, the methodology can also be applied to other planetary magnetospheres with intrinsic magnetic fields. For instance, this approach could be extended to analyze magnetic field data from BepiColombo, which is expected to arrive at Mercury in November 2026. Observations in the Jovian system are no exception: Juno has conducted several flybys at the Galilean moons, and JUICE is expected to orbit Jupiter from 2031.