Chae‐Woo Jun

Abstract We performed a comprehensive statistical study of electromagnetic ion cyclotron (EMIC) waves observed by the Van Allen Probes and Exploration of energization and Radiation in Geospace satellite (ERG/Arase). From 2017 to 2018, we identified and categorized EMIC wave events with respect to wavebands (H + and He + EMIC waves) and relative locations from the plasmasphere (inside and outside the plasmasphere). We found that H + EMIC waves in the morning sector at L > 8 are predominantly o

Abstract To understand the generation and propagation processes of electromagnetic ion cyclotron (EMIC) waves under different geomagnetic conditions in the inner magnetosphere, we performed a statistical study of EMIC wave properties observed by the Van Allen Probes from February 2013 to December 2016. We divided EMIC waves into two groups: those associated with and those occurring without injections observed by the Geostationary Operational Environmental Satellites (GOES‐13 and GOES‐15). We fou

Abstract To understand the relationship between generation of electromagnetic ion cyclotron (EMIC) waves and energetic particle injections, we performed a statistical study of EMIC waves associated with and without injections based on the Van Allen Probes (Radiation Belt Storm Probes) and Geostationary Operational Environmental Satellite (GOES; GOES‐13 and GOES‐15) observations. Using 47 months of observations, we identified wave events seen by the Van Allen Probes relative to the plasmapause an

We investigate possible generation mechanisms of Pc1 pearl structures using multi-point induction magnetometers in Athabasca in Canada, Magadan in Russia, and Moshiri in Japan. We selected two Pc1 pulsations that were simultaneously observed at the three stations and applied a polarization analysis. In case 1, on 8 April 2010, Pc1 pearl structures were slightly different in some time intervals at different stations, and their polarization angles varied depending on the frequencies at the three s

Abstract We performed a statistical study of electromagnetic ion cyclotron (EMIC) wave distributions and their coupling with energetic protons in the inner magnetosphere using the Arase satellite data from May 2017 to December 2020. We investigated the energetic proton pitch‐angle distributions and partial thermal pressures associated with EMIC waves using inter‐calibrated proton data in the energy range of 30 eV/q–187 keV/q. With a cold plasma approximation, we computed the proton minimum reson

Abstract We investigate pearl structures (amplitude modulations) of Pc1 pulsations simultaneously observed at Athabasca (ATH, 54.7°N, 246.7°E, L = 4.3) in Canada, Magadan (MGD, 60.1°N, 150.7°E, L = 2.6) in Russia, and Moshiri (MOS, 44.4°N, 142.3°E, L = 1.5) in Japan. From 6 years of ground observations, from 2008 to 2013, we selected 84 Pc1 events observed simultaneously at the longitudinally separated stations (ATH and MGD) and 370 events observed at the latitudinally separated stations (MGD an

Abstract During the May 2024 storm, the minimum Dst index was approximately −412 nT, marking the largest geomagnetic storm of the past decade. This event caused the inner edge of the ring current to penetrate deeply into the inner magnetosphere during the main phase of the storm. We present observations of high‐frequency electromagnetic ion cyclotron (HF EMIC) wave activity during this intense geomagnetic storm using data from the Arase satellite. Arase observations showed that HF EMIC waves wit

Abstract Using the Arase and Van Allen Probes satellite observations, we investigate the nonlinear electromagnetic ion cyclotron (EMIC) rising‐tone (RT) emissions with an increase of the solar wind dynamic pressure in the dayside magnetosphere. We find that EMIC RT emissions are accompanied by the extended dayside uniform zone (DUZ) over |MLAT| < 25° due to the dayside magnetospheric compression by an increase in P dyn . Using the observed plasma and magnetic field data, we modeled the thresh

We statistically investigated the properties of low-latitude Pi2 pulsations using Bohyun (BOH, Mlat = <TEX>$29.8^{\circ}$</TEX>, L = 1.35) ground magnetometer data in 2008. For this 1-year interval, 582 Pi2 events were identified when BOH was in the nightside from 1800 to 0600 local times. We found the following Pi2 characteristics. (1) The occurrence distribution of Pi2s is relatively constant in local times. (2) The Pi2 frequency varies in local times. That is, Pi2 pulsations in postmidnight s

Abstract This study demonstrates the influence of electromagnetic ion cyclotron (EMIC) rising‐tone emissions on relativistic electrons in the inner magnetosphere using data obtained from the Van Allen Probes and Arase satellites. We find that the intense EMIC rising‐tone emissions occur during the increase in the solar wind pressures, creating favorable conditions for triggering nonlinear wave growth. The strong flux drop‐out of relativistic electrons in the parallel directions of the magnetic f

We performed a statistical study of electromagnetic ion cyclotron (EMIC) wave distributions and their coupling with energetic protons in the inner magnetosphere using the Arase satellite data from May 2017 to December 2020. We investigated the energetic proton pitch-angle distributions and partial thermal pressures associated with EMIC waves using inter-calibrated proton data in the energy range of 30 eV/q-187 keV/q. With a cold plasma approximation, we computed the proton minimum resonance ener