[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P31] Statistical investigation of Poynting vectors of chorus emissions observed by the Arase satellite

*Takaramoto Kouta¹, Satoshi Kurita¹, Hirotsugu Kojima¹, Yoshiya Kasahara², Shoya Matsuda³, Ayako Matsuoka⁴, Yoshizumi Miyoshi⁵, Iku Shinohara⁶, Satoko Nakamura⁵ (1.Research Institute for Sustainable Humanosphere, Kyoto University, 2.Emerging Media Initiative, Kanazawa University, 3.Kanazawa University, 4.Data Analysis Center for Geomagnetism and Space Magnetism,Graduate School of Science, Kyoto University, 5.Institute for Space-Earth Environmental Research, Nagoya University, 6.Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science)

Keywords:The Arase satellite, Chorus

Chorus waves are a type of plasma wave propagating in the magnetosphere.

Chorus waves are frequently observed in the frequency range from 0.2 to 0.7 times

of electron gyrofrequency, fce, and often show a gap of wave power near 0.5fce. The

waves below and above 0.5fce are called lower-band chorus (LBC) and upper-band

chorus (UBC), respectively. Previous studies show that these waves are excited

near the magnetic equator and propagate toward higher latitudes. On the other

hand, the difference of radiation characteristics between UBC and LBC is not clear.

The purpose of this study is to clarify the radiation characteristics of chorus waves

by analyzing data obtained by the Arase satellite.

This study evaluates the Poynting vector of chorus waves using electric and magnetic

field waveforms observed by the Arase satellite. We computed the Poynting

vector parallel to the ambient magnetic field. The magnitude of the northward and

southward Poynting vector is averaged over the bandwidth of 0.05fce and 1 second

time interval, and is sorted by the distance from the magnetic equator. Frequency

spectral feature such as rising tones are also considered in the analysis. In the case

of rising tone LBC, as the frequency of the chorus increases, the region where the

large Poynting flux is measured moves the opposite direction compared to the wave

propagation direction. In the case of rising tone UBC, the region where the large

Poynitng flux is measured shrinks toward the equator as the frequency of the wave

increases. On the other hand, waves without frequency chirping do not show the

frequency dependence of the region where the large Poynting flux is measured.

From these results, we propose that the excitation region of the rising tone chorus moves as the frequency increases.

We also propose that the excitation region for waves without characteristic frequency

chirping does not depend on the wave frequency.