講演情報
[PEM13-P31]あらせ衛星観測に基づくコーラス放射のポインティングベクトルに関する統計解析
*宝本 航大1、栗田 怜1、小嶋 浩嗣1、笠原 禎也2、松田 昇也3、松岡 彩子4、三好 由純5、篠原 育6、中村 紗都子5 (1.京都大学生存圏研究所、2.金沢大学学術メディア創成センター、3.金沢大学、4.京都大学 理学研究科 地磁気世界資料解析センター、5.名古屋大学宇宙地球環境研究所、6.宇宙航空研究開発機構/宇宙科学研究所)
キーワード：
あらせ衛星、コーラス
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.
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.