[P-EM17] Space Plasma Physics: Theory and Simulation

[PEM17-02] Observational evidence of nonlinear growth of whistler-mode waves in an outflow of magnetopause reconnection

*Naritoshi Kitamura¹, Takanobu Amano², Masahiro Kitahara³, Yoshiharu Omura⁴, Scott A. Boardsen^5,6, Yoshizumi Miyoshi¹, Satoko Nakamura¹, Masafumi Shoji¹, Yuto Katoh³, Hirotsugu Kojima⁴, Daniel J. Gershman⁵, Yoshifumi Saito⁷, Masafumi Hirahara¹, Shoichiro Yokota⁸, Barbara L. Giles⁵, Craig J. Pollock⁹, Olivier Le Contel¹⁰, Christopher T. Russell¹¹, Robert J. Strangeway¹¹, Per-Arne Lindqvist¹², Robert E. Ergun¹³, James L. Burch¹⁴ (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.Department of Earth and Planetary Science, Graduate School of Science, the University of Tokyo, 3.Department of Geophysics, Graduate School of Science, Tohoku University, 4.Research Institute for Sustainable Humanosphere, Kyoto University, 5.NASA Goddard Space Flight Center, 6.Goddard Planetary Heliophysics Institute, University of Maryland in Baltimore, 7.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 8.Department of Earth and Space Science, Graduate School of Science, Osaka University, 9.Denali Scientific, 10.Laboratoire de Physique des Plasmas, CNRS/Ecole Polytechnique/Sorbonne Université/Université Paris-Sud/Observatoire de Paris, 11.Department of Earth, Planetary, and Space Science, University of California, Los Angeles, 12.Royal Institute of Technology, 13.Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, 14.Southwest Research Institute)

Keywords:Whistler-mode wave, Magnetic reconnection, MMS spacecraft

In this presentation, we show observational results of nongyrotropic electrons close to the cyclotron resonance velocity, which is a key feature of nonlinear growth of whistler-mode waves, using data obtained by the Magnetospheric Multiscale (MMS) spacecraft in an outflow of asymmetric reconnection (reconnection jet) at the dayside magnetopause. Whistler-mode waves are one of the electromagnetic plasma waves, which play important roles in efficient pitch-angle scattering and acceleration of electrons in solar wind, collisionless shock waves, and planetary magnetospheres. The nonlinear wave-particle interaction theory for coherent large amplitude waves predicts that resonant electrons exhibit nongyrotropy due to phase trapping motion around resonance velocities in the presence of an appropriate inhomogeneity. The nongyrotropic electrons exchange energy and momentum with waves efficiently. Here we show examples of nongyrotropic electrons close to the cyclotron resonance velocity during whistler-mode wave events in an outflow of asymmetric reconnection (reconnection jet) at the dayside magnetopause as the observational evidence of nonlinear wave growth. Using measurements by the Fast Plasma Investigation Dual Electron Spectrometer (FPI-DES) and the search-coil magnetometer (SCM), we identified electron flux hole events that induce wave growth; a hole at an appropriate relative phase angle to the whistler-mode wave magnetic field appeared only close to the cyclotron resonance velocity at both of regions where the magnetic field direction was close to or largely different from that of the magnetosphere. The magnitudes of the gradient of the magnetic field intensity along the magnetic field line during such time intervals are consistent with an appropriate magnitude to cause phase trapping of resonant electrons. In these events, a loss cone of the magnetospheric electrons played an important role to generate temperature anisotropy around the cyclotron resonance velocity.