In-situ observations of nonlinear wave particle interaction of electromagnetic ion cyclotron waves

Thursday, 18 December 2014
Masafumi Shoji1, Yoshizumi Miyoshi2, Kunihiro Keika2, Yuto Katoh3, Vassilis Angelopoulos4, Satoko Nakamura5 and Yoshiharu Omura6, (1)Nagoya University, Solar-Terrestrial Environment Laboratory, Nagoya, Japan, (2)Nagoya University, Nagoya, Japan, (3)Tohoku University, Sendai, Japan, (4)University of California Los Angeles, Los Angeles, CA, United States, (5)Kyoto University, Graduate School of Science, Kyoto, Japan, (6)RISH Research Institute for Sustainable Humanosphere, Kyoto, Japan
Direct measurement method for the electromagnetic wave and space plasma interaction has been suggested by a computer simulation study [Katoh et al., 2013], so-called Wave Particle Interaction Analysis (WPIA). We perform the WPIA for rising tone electromagnetic ion cyclotron (EMIC) waves (so-called EMIC triggered emissions), of which generation mechanism is essentially the same as the chorus emissions. THEMIS observation data (EFI, FGM, and ESA) are used for the WPIA. In the WPIA, we calculate (1) the inner product of the wave electric field and the velocity of the energetic protons: Wint, (2) the inner product of the wave magnetic field and the velocity of the energetic protons: WBint, and (3) the phase angle ζ between the wave magnetic field and the perpendicular velocity of the energetic protons. The values of (1) and (2) indicate the existence of the resonant currents inducing the nonlinear wave growth and the frequency change, respectively. We find the negative Wint and positive WBint at the nonlinear growing phase of the triggered emission as predicted in the theory [e.g. Omura and Nunn, 2011, Shoji and Omura, 2013]. In histogram of (3), we show the existence of the electromagnetic proton holes in the phase space generating the resonant currents. We also perform a hybrid simulation and evaluate WPIA method for EMIC waves. The simulation results show good agreement with the in-situ THEMIS observations.