3:30 PM - 5:00 PM
[PPS06-P27] Statistical investigation of electrostatic cyclotron harmonic waves observed by ARTEMIS in the Vicinity of the Moon
Electron Cyclotron Harmonic Wave (ECH) is a type of plasma wave that is excited by the electron Bernstein mode wave. The wave is characterized by a harmonic structure with a spectral peak at integer multiples of the electron cyclotron frequency. It has been confirmed that ECH is excited under the plasma environment around the Moon formed by the interaction between space plasma and the Moon, which does not have a large intrinsic magnetic field and no atmosphere.
Previous studies performed analysis of ECH near the Moon using data from the lunar orbiter KAGUYA, which orbits at an altitude of about 100 km above the Moon’s surface. However, research on ECH at even higher altitudes has not been performed.
Therefore, this study aims to elucidate the relationship between ECH excitation and the plasma environment around the Moon using data from the ARTEMIS satellite, which orbits the Moon in an elliptical orbit and observes a wider altitude compared with the KAGUYA observation.
We collected ECH events observed by the ARTEMIS satellites for six years from 2016 to 2021. We then analyzed the ECH data using the plasma, dynamic spectra of wave electric fields, and DC magnetic field measurements by the ARTEMIS satellites.
We found that the ECHs observed at the altitude of the ARTEMIS satellites are categorized into three types of spectral structures: those with a peak near the UHR frequency (Type 1), those with multiple spectral peaks between integer multiples of the cyclotron frequency (Type 2), and those with both Type 1 and Type 2 (Type 3).
For each type of ECH, we investigated the plasma environment around the Moon and the relative location between the Moon and the ARTEMIS satellites. The results showed that Type 1 was observed in the both plasma sheet and the lobe, while Type 1 preferentially appeared on the dayside of the Moon in the lobe. Type 2 was observed only in the lobe, although the number of observations was small. Type 3 was also observed in the lobe, but more frequently in the dayside and nightside of the Moon in the plasma sheet.
Analysis of the ECH wave events observed by KAGUYA has revealed that the unique electron velocity distributions near the Moon strongly relate to the excitation of ECH. In this presentation, the electron velocity distribution for each type of ECH will also be discussed.
Previous studies performed analysis of ECH near the Moon using data from the lunar orbiter KAGUYA, which orbits at an altitude of about 100 km above the Moon’s surface. However, research on ECH at even higher altitudes has not been performed.
Therefore, this study aims to elucidate the relationship between ECH excitation and the plasma environment around the Moon using data from the ARTEMIS satellite, which orbits the Moon in an elliptical orbit and observes a wider altitude compared with the KAGUYA observation.
We collected ECH events observed by the ARTEMIS satellites for six years from 2016 to 2021. We then analyzed the ECH data using the plasma, dynamic spectra of wave electric fields, and DC magnetic field measurements by the ARTEMIS satellites.
We found that the ECHs observed at the altitude of the ARTEMIS satellites are categorized into three types of spectral structures: those with a peak near the UHR frequency (Type 1), those with multiple spectral peaks between integer multiples of the cyclotron frequency (Type 2), and those with both Type 1 and Type 2 (Type 3).
For each type of ECH, we investigated the plasma environment around the Moon and the relative location between the Moon and the ARTEMIS satellites. The results showed that Type 1 was observed in the both plasma sheet and the lobe, while Type 1 preferentially appeared on the dayside of the Moon in the lobe. Type 2 was observed only in the lobe, although the number of observations was small. Type 3 was also observed in the lobe, but more frequently in the dayside and nightside of the Moon in the plasma sheet.
Analysis of the ECH wave events observed by KAGUYA has revealed that the unique electron velocity distributions near the Moon strongly relate to the excitation of ECH. In this presentation, the electron velocity distribution for each type of ECH will also be discussed.