SM032-0012
Modulation of energy transfer between hot protons and electromagnetic ion cyclotron waves by compressional Pc5 ULF waves

Monday, 14 December 2020
Poster
Naritoshi Kitamura1, Masafumi Shoji2, Masahiro Kitahara2, Satoko Nakamura2, Takanobu Amano3, Yoshiharu Omura4, Yoshizumi Miyoshi2, Hiroshi Hasegawa5, Yuto Katoh6, Yoshifumi Saito7, Mariko Teramoto8, Reiko Nomura7, Shoichiro Yokota9, Daniel J Gershman10, Scott A Boardsen10,11, Adolfo F. Vinas10, Barbara L Giles10, William R Paterson12, Craig J Pollock10, Christopher T Russell13, Robert J Strangeway14, Narges Ahmadi15, Per-Arne Lindqvist16, Robert Ergun17, Stephen A Fuselier18 and James L Burch19, (1)University of Tokyo, Bunkyo-ku, Japan, (2)ISEE, Nagoya University, Nagoya, Japan, (3)The University of Tokyo, Bunkyo-ku, Japan, (4)Kyoto University, Research Institute for Sustainable Humanosphere, Kyoto, Japan, (5)JAXA Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, Sagamihara, Japan, (6)Tohoku University, Sendai, Japan, (7)JAXA Japan Aerospace Exploration Agency, Sagamihara, Japan, (8)Nagoya University, ISEE, Nagoya, Japan, (9)Osaka University, Department of Earth and Space Science, Osaka, Japan, (10)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (11)University of Maryland Baltimore County, Goddard Planetary Heliophysics Institute, Baltimore, MD, United States, (12)NASA Goddard Space Flight Center, Heliophysics Science Division, Greenbelt, MD, United States, (13)University of California, Los Angeles, CA, United States, (14)University of California Los Angeles, Earth, Planetary, and Space Sciences, Los Angeles, CA, United States, (15)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (16)KTH Royal Institute of Technology, Stockholm, Sweden, (17)Univ Colorado, Boulder, CO, United States, (18)Southwest Research Institute, San Antonio, TX, United States, (19)Southwest Research Institute San Antonio, San Antonio, TX, United States
Abstract:
Magnetospheric Multiscale (MMS) spacecraft observed many enhancements of electromagnetic ion cyclotron (EMIC) waves mainly at troughs of magnetic field intensity by a compressional Pc5 ULF wave at the duskside outer magnetosphere. The compressional ULF wave had some characteristics of mirror mode type structures that the magnetic and ion pressures were in antiphase. To identify the energy transfers between hot anisotropic protons and EMIC waves directly, we apply the Wave-Particle Interaction Analyzer (WPIA) method to the burst data obtained by the four MMS spacecraft. The energy transfer was identified around the cyclotron resonance velocity, which is derived from the wavelength estimation of the EMIC wave that used the phase difference between MMS1 and MMS2. The width of the energy transfer in the velocity space around the cyclotron resonance velocity is roughly consistent with the width of the ion hole that is predicted by the nonlinear theory. The occurrence of energy transfer was limited only around the center of troughs of magnetic field intensity, which corresponds to the maxima of ion pressure in the compressional ULF wave. This result strongly suggests that the EMIC wave generation is modulated by ULF waves, and preferential locations for the cyclotron resonant energy transfer are the troughs of magnetic field intensity. A decrease in the cyclotron resonance velocity due to a decrease in magnetic field intensity and an increase in the hot proton pressure in the troughs of magnetic field intensity can enhance the growth rate of EMIC waves in the stage of initial linear growth at the upstream region. Furthermore, the decrease in the cyclotron resonance velocity and the increase in the hot proton pressure will be able to enhance the nonlinear growth rate owing to an increase in the number of particles around the cyclotron resonance velocity. Due to the compressional ULF wave, regions of the cyclotron resonant energy transfer became probably very localized (order of only a few times of the gyroradii of hot resonant protons) in the direction of magnetic local time. Weak EMIC waves appeared even around the peaks of the magnetic field intensity. An antisymmetric standing of the compressional ULF structure and EMIC wave generation (and propagation) at the opposite side of the magnetic equator can explain the feature.
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