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.
Bibliographical noteFunding Information:
The Van Allen Probes data used in this study have been opened to the public from the University of Minnesota (http://www.space.umn.edu/missions/rbspefw-home-university-of-minnesota/). We acknowledge useful discussions with C. Klezing, Y. Kato, and D.-H. Lee. Science data of the ERG (Arase) satellite were obtained from the ERG Science Center operated by ISAS/JAXA and ISEE/Nagoya University (https://ergsc.isee.nagoya-u.ac.jp/index.shtml.en). In the present data, we use level 1-prime WFC version 7 data and level-2 MGF 64 Hz v01.01. The Arase satellite data will be publicly available via ERG Science Center on a project-agreed schedule. This study is supported by Grants-in-Aid for Scientific Research (14J02108, 15H05815, 16H06286, 16J02163, 17K05668, 17K14400, 17K14402 and 26800257) of Japan Society for the Promotion of Science (JSPS). This research was supported by the Natural Environment Research Council (NERC) Highlight Topic grants NE/P01738X/1 (Rad-Sat) and NE/R016038/1. This study was supported by JSPS Bilateral Open Partnership Joint Research Projects. We also acknowledge support from the MEYS LTAUSA17070 project and from the Czech Academy of Sciences through the JSPS-17-14 project and through the Praemium Academiae award.
© 2019. The Authors.
- M/Q = 2 ions
- Van Allen Probes
- magnetsonic waves