7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Direct measurement of energy transfer from magnetosonic waves toelectromagnetic ion cyclotron waves through heating of cold ions in space

K. Asamura1, M. Shoji2, Y. Miyoshi2, Y. Kasahara3, Y. Kasaba4, A. Kumamoto4, F. Tsuchiya4S. Matsuda3, A. Matsuoka5, M. Teramoto6, Y. Kazama7, I. Shinohara1
1ISAS, JAXA2
ISEE, Nagoya University
3
Graduate school of natural science, Kanazawa University4
Graduate school of science, Tohoku University
5
Graduate school of science, Kyoto University
6
Graduate school of engineering, Kyushu Institute of Technology
7Academia Sinica, Taiwan
e-mail (speaker): asamura@stp.isas.jaxa.jp
We applied a novel wave-particle interaction analysis
method (WPIA: Wave-Particle Interaction Analyzer) toobserved plasma particle and field data obtained by theArase satellite in the terrestrial inner magnetosphere.
WPIA method[1] has been applied to investigate theenergy transfer between plasma waves and particles. TheWPIA method calculates the inner product of the wave
electric field vector and particle velocity vector,
multiplies by the particle charge, and then, sums (𝑊𝐸𝑖𝑛𝑡)in velocity space. A positive 𝑊𝐸𝑖𝑛𝑡 corresponds to theJoule heating of particles by plasma waves, whereas anegative 𝑊𝐸𝑖𝑛𝑡 indicates wave growth due to particles.
Application of the WPIA method to in-situ observation
data of plasma particles and waves provides direct
evidence of energy transfer between them. However,there are only several examples[2-6] of analysis based on
the WPIA method for space plasma and wave data so far,since the WPIA method is rather new method.
Flux enhancement of low-energy ions (~100eV) in acomponent perpendicular to the background magnetic
field direction was observed by Arase on February 10,
2018. At the same time, Arase detected magnetic field
fluctuations around 11 Hz and 2 Hz (Figure 1(a)).
Investigation of polarization and wave normal angles
identified these waves as magnetosonic waves (MSWs)
and electromagnetic ion cyclotron (EMIC) waves,respectively.

Figure 1(d) shows the calculated 𝑊𝐸𝑖𝑛𝑡 for theobserved MSW activity. 𝑊𝐸𝑖𝑛𝑡 was mostly positive
although there were a few exceptions with a negative
𝑊𝐸𝑖𝑛𝑡. A positive 𝑊𝐸𝑖𝑛𝑡 indicates that the MSWs gave
their energies to low-energy protons. Figure 1(e) shows
the results of the WPIA calculations for the EMIC waves.
𝑊𝐸𝑖𝑛𝑡 is negative throughout the event period with a clearenhancement. Our results suggest that the plasma sheetand ring current ions transfer some energy to thelow-energy ions through excitation and damping ofMSWs in the inner magnetosphere. Furthermore, aportion of the transferred energy is then converted toexcite EMIC waves. Such cross-energy coupling isimportant for the heating of plasmaspheric plasmas andmay contribute to the generation of EMIC waves and thenon-thermal population of the inner magnetosphere, suchas ion cloaks.
References[1] Y. Katoh et al., Ann. Geophys., 31, 503 (2013)[2] M. Shoji et al., Geophys. Res. Lett., 44, 8730 (2017)[3] N. Kitamura et al., Science, 361, 1000 (2018)[4] M. Shoji et al., Sci. Rep., 11, 13480 (2021)[5] K. Asamura et al., Phys. Rev. Lett., 127, 245101(2021)[6] N. Kitamura et al., Nat. Commun., 13:6259 (2022)

Figure 1. (a-c) Particle (proton) flux and magnetic field fluctuations observed by the Arase satellite. (a) Dynamic
spectra of wave magnetic energy in the spin axis direction of Arase, (b) Energy spectra of omnidirectional protonenergy fluxes, (c) Pitch angle distribution of proton energy fluxes at an energy of 114eV. (d-e) Results of WPIA
calculations. 𝑊𝐸𝑖𝑛𝑡 for (d) MSW activities and (e) EMIC waves. Three solid lines indicate calculated values andconfidence intervals.