Statistical characteristics of EMIC waves: Van Allen Probe observations

• Published in: Journal of geophysical research. Space physics 2015-06, Vol.120 (6), p.4400-4408
• Main Authors: Wang, Dedong, Yuan, Zhigang, Yu, Xiongdong, Deng, Xiaohua, Zhou, Meng, Huang, Shiyong, Li, Haimeng, Wang, Zhenzhen, Qiao, Zheng, Kletzing, C. A., Wygant, J. R.
• Format: Article
• Language: English
• Subjects: Cyclotrons; distribution; Dynamic pressure; EMIC waves; Helium; Hydrogen; Ion cyclotron waves; Jupiter; Magnetic fields; Magnetism; Magnetospheres; Night; Noon; Plasmapause; Plasmasphere; Satellite-borne instruments; Solar wind; Space probes
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2015JA021089

Utilizing the data from the magnetometer instrument which is a part of the Electric and Magnetic Field Instrument Suite and Integrated Science instrument suite on board the Van Allen Probe A from September 2012 to April 2014, when the apogee of the satellite has passed all the magnetic local time (MLT) sectors, we obtain the statistical distribution characteristics of electromagnetic ion cyclotron (EMIC) waves in the inner magnetosphere over all magnetic local times from L = 3 to L = 6. Compared with the previous statistical results about EMIC waves, the occurrence rates of EMIC waves distribute relatively uniform in the MLT sectors in lower L shells. On the other hand, in higher L shells, there are indeed some peaks of the occurrence rate for the EMIC waves, especially in the noon, dusk, and night sectors. EMIC waves appear at lower L shells in the dawn sector than in other sectors. In the lower L shells (L  4) the occurrence rates of EMIC waves are most significant in the dusk sector, implying the important role of the plasmapause or plasmaspheric plume in generating EMIC waves. We have also investigated the distribution characteristics of the hydrogen band and the helium band EMIC waves. Surprisingly, in the inner magnetosphere, the hydrogen band EMIC waves occur more frequently than the helium band EMIC waves. Both of them have peaks of occurrence rate in noon, dusk, and night sectors, and the hydrogen band EMIC waves have more obvious peaks than the helium band EMIC waves in the night sector, while the helium band EMIC waves are more concentrated than the hydrogen band EMIC waves in the dusk sector. Both of them occur significantly in the noon sector, which implies the important role of the solar wind dynamic pressure. Key Points The distribution character of EMIC waves in lower L Shells is studied EMIC waves distribute relatively uniform in the MLT sectors in lower L shells EMIC waves in the dawn sector at low L shell are significant