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

Duct propagation of whistler-mode chorus emissions under the presence of ULF
waves
Kohki Tachi1, Yuto Katoh1, Atsushi Kumamoto1, Fuminori Tsuchiya1, Yasumasa Kasaba1, Satoshi
Kurita2, Yoshiya Kasahara3, Shoya Matsuda3, Ayako Matsuoka4, Mariko Teramoto,5 Yoshizumi
Miyoshi6, Satoko Nakamura6, Iku Shinohara7
1
Dept. Geophys., Grad. Sch..Sci., Tohoku Univ., 2RISH, Kyoto Univ., 3Kanazawa Univ., 4KyotoUnive., 5Kyutech., 6ISEE, Nagoya Univ., 7ISAS/JAXA
e-mail (speaker): tachi.koki.q5@dc.tohoku.ac.jp

Whistler-mode chorus wave is a coherent

index on the variation of either the magnetic field orelectromagnetic plasma wave. Accordance with previous

number density; a decrease in the magnetic fieldstudies, chorus emissions perform important roles; theintensity leads to a refractive index change

acceleration of relativistic electrons in the radiation belt

corresponding to an increase in the electron density.

and the pitch angle scattering of keV electrons inducing

Where the range of the variation is less than 10% of thediffuse/pulsating aurora. Recent research suggests thatbackground level, both of effects to the refractive index

the high latitude propagation by the duct propagation ofare comparable.

chorus leads to the precipitation of relativistic electrons.

Next, we examine whether the magnetic field

In the present study, we investigate the effect of ULF

fluctuations observed in the event resulted in significant

waves on the duct propagation of whistler-mode waves.

refractive index changes. Here we assume that theWe analyze the Arase satellite data. During the timenumber density of the background plasma is constantinterval from 21:30 UT to 22:00 UT, the Arase satellite

during the event. The observation result shows thatobserved chorus emissions and ULF waves

chorus emissions propagating parallel to the backgroundsimultaneously. The Arase satellite was located atmagnetic field appear at timings corresponding to theL~6.3-6.1, 04:00-04:12MLT, and from -12.7 to -7.4

decrease of the total magnetic field due to thedegrees MLAT. During this event, chorus was shown tocompressional component of ULF waves. The observedpropagate parallel to the magnetic field lines up to aproperty can be explained by the model we propose. In

magnetic latitude exceeding 10 degrees, suggesting theaddition, we discuss the frequency dependency of duct

possibility of duct propagation. We examine the effects

width.

of ULF waves on the duct propagation of chorus

We also consider the density variation during theemissions and propose a model of the duct propagation

event with MHD equation. We estimate that the phaseof whistler-mode waves due to the contribution of therelation between compressional component of ULF andcompressional component of ULF waves.

cold electron density is anti-correlation in the case of 𝛽>At first, we evaluate how effective the magnetic

1, corresponding to the event we analyzed.

variation changes refractive index. Based on thedispersive relation of whistler mode wave, the refractive
index depends on not only the density but also magnetic
field intensity [1]. Setting the amplification factor x andReferences

y for the magnetic field intensity and electron density,[1] Smith et al., (1960) Journal of Geophysical Researchrespectively, we obtain a dependence of the refractive(1896-1977)