![]() In this study, we used the high-resolution (64 samples per second) level-3 DC magnetic field vector data in the solar magnetic coordinate system. The ambient magnetic field is also measured by the magnetometer of EMFISIS. ![]() The Electric and Magnetic Field Instrument and Integrated Science (EMFISIS) aboard the RBSP measures three components of the electric field and three components of the magnetic field below 12 kHz (Kletzing et al., 2013). We also used the level-2 definitive orbit data of Arase (Miyoshi, Shinohara, & Jun, 2018). In addition, we used the DC magnetic field data measured by the MGF to calculate the ion cyclotron frequencies and the ambient magnetic field direction. We used the level-2 three-dimensional proton flux data (Asamura, Miyoshi, & Shinohara, 2018) to analyze the energy-time diagrams, and the level-3 pitch-angle distribution data (Asamura et al., 2021). The low-energy particle experiments-ion mass analyzer (LEP-i) (Asamura, Kazama, et al., 2018) measures ions with an energy range from 0.01 to 25 keV/q. To determine the ambient electron density from the upper hybrid resonance (UHR) frequencies, we used the level-2 electric field spectrum data observed by the High Frequency Analyzer (HFA) (Kasahara, Kumamoto, et al., 2018 Kumamoto et al., 2018). ![]() We used the level-2 electric and magnetic field waveforms observed by the Electric Field Detector (EFD) (Kasaba et al., 2017 Kasahara et al., 2020 Kasahara, Kasaba, et al., 2018) and the Magnetic Field Experiment (MGF) (Matsuoka, Teramoto, Imajo, et al., 2018 Matsuoka, Teramoto, Nomura, et al., 2018) aboard Arase (Miyoshi, Shinohara, Takashima, et al., 2018) for the EMIC wave analysis. Further, we investigate the differences in the wave properties of fine-structured EMIC waves observed in each latitude, and the thermal ion heating due to fine-structured EMIC waves, using observations from these four sites. We report that the growth of the observed fine-structured EMIC waves was associated with the periodic electron density irregularities found in the midlatitude region. In this study, we present the results of the coordinated observation of fine-structured EMIC waves on Apby Arase (midlatitude region), Van Allen Probe A (Radiation Belt Storm Probes A, hereinafter called RBSP-A) (equatorial region), and induction magnetometers placed on the Gakona station of the “study of dynamical variation of Particles and Waves in the INner magnetosphere using Ground-based network observations” (PWING) magnetometer and the Dawson station of the “Canadian Array for Realtime Investigations of Magnetic Activity” (CARISMA) magnetometer array. EMIC waves that cause IPA work for MeV electron scattering (e.g., Miyoshi et al., 2008) and the density irregularity of the topside ionosphere (Kim et al., 2021). Ozaki et al. ( 2018) reported 1 Hz range modulation of IPAs and concluded that the modulation was due to intermittent proton precipitation or sub/relativistic electrons scattered by repetitive bursts of fine-structured EMIC waves. This is evidence that fine-structured EMIC waves scatter energetic protons, which then precipitate into the ionosphere. ![]() Sakaguchi et al. ( 2015) and Nomura et al. ( 2016) found that fine-structured EMIC waves cause isolated proton auroras (IPAs). Several recent studies have examined the role of fine-structured EMIC waves from the perspective of wave-particle interaction. Similar questions about the BWP model were raised by Erlandson and Anderson ( 1996) and Mursula et al. ( 2001). They concluded that these observation results cannot be explained by the bouncing wave packet (BWP) model proposed by Jacobs and Watanabe ( 1964) and Obayashi ( 1965). For example, Usanova et al. ( 2008) presented simultaneous ground-satellite observations of fine-structured EMIC waves and reported that the repetition periods of fine-structured EMIC waves observed on the ground and on the Time History of Events and Macroscale Interactions During Substorms (THEMIS) spacecraft were almost identical. Multipoint measurement of fine-structured EMIC waves reveals their propagation mechanism, formation mechanism, and wave-particle interaction along their propagation path. Fine-structured electromagnetic ion cyclotron (EMIC) waves are one type of EMIC mode waves, and ground-based Pc1 studies have reported that they are composed of clear repetitive bursts of characteristic rising tones in a typical frequency range of 0.2–5 Hz (Fukunishi et al., 1981 Troitskaya & Gul'elmi, 1967).
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