研究者詳細 - JUN Chae-Woo

The Relationship Between EMIC Wave Properties and Proton Distributions Based on Van Allen Probes Observations 査読有り

Chao Yue, Chae‐Woo Jun, Jacob Bortnik, Xin An, Qianli Ma, Geoffrey D. Reeves, Harlan E. Spence, Andrew J. Gerrard, Matina Gkioulidou, Donald G. Mitchell, Craig A. Kletzing

Geophysical Research Letters 46 巻 ( 8 ) 頁： 4070 - 4078 2019年4月

Discovery of 1 Hz Range Modulation of Isolated Proton Aurora at Subauroral Latitudes 査読有り Open Access

Ozaki M., Shiokawa K., Miyoshi Y., Kataoka R., Connors M., Inoue T., Yagitani S., Ebihara Y., Jun C., Nomura R., Sakaguchi K., Otsuka Y., Uchida H., Schofield I., Danskin D.

Geophysical Research Letters 45 巻 ( 3 ) 頁： 1209 - 1217 2018年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geophysical Research Letters

Isolated proton aurora (IPA) is a manifestation of the wave-particle interaction visible at subauroral latitudes, with activity on many timescales. We herein present the first observational evidence of rapid luminous modulation of IPA correlated with simultaneously observed Pc1 waves observed on the ground, which are equivalent to the electromagnetic ion cyclotron (EMIC) waves in the magnetosphere. The fastest luminous modulation of IPA was observed in the 1 Hz frequency range, which was twice the frequency of the related Pc1 waves. The time lag between variations of Pc1 wave power and the IPA luminosity suggests that the source regions of IPA are distributed near the magnetic equator, suggesting an EMIC wave-energetic (a few tens of keV) proton or relativistic (MeV or sub-MeV) electron interaction. The generation mechanism of this 1 Hz luminous modulation remains an open issue, but this study supports the importance of nonlinear pitch angle scattering via wave-particle interactions.

DOI： 10.1002/2017GL076486

Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes 査読有り Open Access

Ozaki M., Shiokawa K., Miyoshi Y., Kataoka R., Yagitani S., Inoue T., Ebihara Y., Jun C., Nomura R., Sakaguchi K., Otsuka Y., Shoji M., Schofield I., Connors M., Jordanova V.

Geophysical Research Letters 43 巻 ( 15 ) 頁： 7859 - 7866 2016年8月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geophysical Research Letters

To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8 s) images of proton-induced N2+ emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100 s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100 s and an unpredicted fast modulation of a few tens of seconds. These results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.

DOI： 10.1002/2016gl070008

Study of Pc1 pearl structures observed at multi-point ground stations in Russia, Japan, and Canada 査読有り

Jun C., Shiokawa K., Connors M., Schofield I., Poddelsky I., Shevtsov B.

Earth, Planets and Space 66 巻 ( 1 ) 2014年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth, Planets and Space

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 stations. Case 2, on 11 April 2010, showed Pc1 pearl structures that were similar at different stations, and their polarization angle was independent of frequency at all three stations. In order to understand these differences, we performed two simple model calculations of Pc1 pearl structures under different conditions. The first model assumes that Pc1 waves propagated from a latitudinally extended source with different frequencies at different latitudes to the observation points, representing beating of these waves in the ionosphere. The second model considers Pc1 waves for which different frequencies are mixed at a point source to cause the beating at the source point, indicating that the Pc1 pearl structures are generated in the magnetosphere. The first model shows slightly different waveforms at different stations. In contrast, the second model shows identical waveforms at different stations. From these results, we conclude that, in case 1, Pc1 pearl structures were caused by beating in the ionosphere. On the other hand, in case 2, they were the result of magnetospheric effects. We suggest that beating processes in the ionosphere could be one of the generation mechanisms of Pc1 pearl structures.

DOI： 10.1186/s40623-014-0140-8

その他リンク： http://link.springer.com/content/pdf/10.1186/s40623-014-0140-8.pdf

Low-latitude Pi2 pulsations during intervals of quiet geomagnetic conditions (K<inf>p</inf>≤1) 査読有り Open Access

Kwon H.J., Kim K.H., Jun C.W., Takahashi K., Lee D.H., Lee E., Jin H., Seon J., Park Y.D., Hwang J.

Journal of Geophysical Research: Space Physics 118 巻 ( 10 ) 頁： 6145 - 6153 2013年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

It has been reported that Pi2 pulsations can be excited under extremely quiet geomagnetic conditions (Kp=0). However, there have been few comprehensive reports of Pi2 pulsations in such a near ground state magnetosphere. To understand the characteristics of quiet-time Pi2 pulsations, we statistically examined Pi2 events observed on the nightside between 1800 and 0600 local time at the low-latitude Bohyun (BOH, L = 1.35) station in South Korea. We chose year 2008 for analysis because geomagnetic activity was unusually low in that year. A total of 982 Pi2 events were identified when Kp≤1. About 80% of the Pi2 pulsations had a period between 110 and 300 s, which significantly differs from the conventional Pi2 period from 40 to 150 s. Comparing Pi2 periods and solar wind conditions, we found that Pi2 periods decrease with increasing solar wind speed, consistent with the result of Troitskaya (1967). The observed wave properties are discussed in terms of plasmaspheric resonance, which has been proposed for Pi2 pulsations in the inner magnetosphere. We also found that Pi2 pulsations occur quasi-periodically with a repetition period of ∼23-38 min. We will discuss what determines such a recurrence time of Pi2 pulsations under quiet geomagnetic conditions. Key Points Pi2 pulsations during quiet geomagnetic conditions Pi2 frequencies depending on solar wind speeds Quasi-periodic Pi2 pulsations with an occurrence rate of about 23-53 min ©2013. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/jgra.50582