Sub-packet structures in the EMIC triggered emission observed by the THEMIS probes

Thursday, 4 September 2014
Regency Ballroom (Hyatt Regency)
Satoko Nakamura, Kyoto University, Graduate School of Science, Kyoto, Japan, Yoshiharu Omura, RISH Research Institute for Sustainable Humanosphere, Kyoto, Japan, Masafumi Shoji, Nagoya University, Solar-Terrestrial Environment Laboratory, Nagoya, Japan; ISAS/JAXA, Sagamihara, Japan, Danny Summers, Memorial University of Newfoundland, Dept of Math and Stats, St John's, NL, Canada and Masahito Nose, Kyoto Univ, Graduate School of Science, Kyoto, Japan
Abstract:
We report observations of electromagnetic ion cyclotron (EMIC) triggered emissions observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes. These phenomena have recently attracted much attention because of their strong nonlinear interaction with energetic particles in the inner magnetosphere[1,2]. For 1400-1445 UT on 9 September 2010, THEMIS A, D, and E observed strong EMIC waves with rising tone emissions. The probes were located near the dayside magnetopause at a radial distance 8 RE from the Earth 13 MLT, and a few degrees of the geomagnetic latitude. During this time interval, the geomagnetic field was very distorted by a variation in the solar wind. We assume these emissions were excited in an extended region near the equator where the field-aligned Bgradient was much reduced because of compression of the magnetosphere by the solar wind. It is found that the rising tone emissions comprise some smaller rising tones, which are called sub-packet structures[3]. We try to interpret each of the observed sub-packets with the nonlinear wave growth theory developed by Omura et al. [4]. The observed relationship between the amplitudes and frequencies of the sub-packets are well explained by the theory, and it is also found that the observed dynamic spectra of the emissions agree well with the threshold and optimum amplitudes for the nonlinear growth.

[1]Omura, Y., and Q. Zhao (2012), Nonlinear pitch angle scattering of relativistic electrons by EMIC waves in the inner magnetosphere, J. Geophys. Res., 117 (A8), doi:10.1029/2012JA017943.

[2]Shoji, M., and Y. Omura (2012), Precipitation of highly energetic protons by helium branch electromagnetic ion cyclotron triggered emissions, J. Geophys. Res., 117 (A12), doi:10.1029/2012JA017933

[3]Shoji, M., and Y. Omura (2013), Triggering process of electromagnetic ion cyclotron rising tone emissions in the inner magnetosphere, J. Geophys. Res. Space Physics, 118, 5553-5561, doi:10.1002/jgra.50523.

[4]Omura, Y., J. Pickett, B. Grison, O. Santolik, I. Dandouras, M. Engebretson, P. M. E. Decreau, and A. Masson (2010), Theory and observation of electromagnetic ion cyclotron triggered emissions in the magnetosphere, J. Geophys. Res., 115 (A7), doi:10.1029/2010JA015300.

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