PPARCセミナー(2024/07/01)
PPARCセミナー(2024/07/01)
(1)
[Name] Riku Kikuchi
[Name] Riku Kikuchi
[Title]
EMIC Waves Converted From Equatorial Noise Due to M/Q = 2 Ions in the Plasmasphere: Observations From Van Allen Probes and Arase
(Y.Miyoshi, 2019)
(Y.Miyoshi, 2019)
[Abstract]
Equatorial noise (EN) emissions are observed inside and outside the plasmapause. EN emissions are referred to as magnetosonic mode waves. Using data from Van Allen Probes and Arase, we found conversion from EN emissions to electromagnetic ion cyclotron (EMIC) waves in the plasmasphere and in the topside ionosphere. A low‐frequency part of EN emissions becomes EMIC waves through branch splitting of EN emissions, and the mode conversion from EN to EMIC waves occurs around the frequency of M/Q = 2 (deuteron and/or alpha particles) cyclotron frequency. These processes result in plasmaspheric EMIC waves. We investigated the ion composition ratio by characteristic frequencies of EN emissions and EMIC waves and obtained ion composition ratios. We found that the maximum composition ratio of M/Q = 2 ions is ~10% below 3,000 km. The quantitative estimation of the ion composition will contribute to improving the plasma model of the deep plasmasphere and the topside ionosphere.
(2)
[Name] Naoko Takatori
[Name] Naoko Takatori
[Title]
① THEMIS Na exosphere observations of Mercury and their correlation with in-situ magnetic field measurements by MESSENGER
② Short-term observations of double-peaked Na emission from Mercury’s exosphere
② Short-term observations of double-peaked Na emission from Mercury’s exosphere
[Abstract]
①The Na exosphere of Mercury is being studied since its discovery in mid ‘80s from Earth-based telescopes, and it has revealed a high dynamics and variability. Although the processes and their relationships characterizing the Herman exosphere generation and dynamics are still not exhaustively understood, there are no doubts on a tight interconnection among the planet’s surface, exosphere, intrinsic magnetic field, the solar wind and the Interplanetary Magnetic Field (IMF). In this paper they analyze an extended dataset of images of the exospheric Na emission, collected from 2009 to 2013, by means of the THEMIS ground-based telescope, in order to perform a comprehensive statistical study of the recurrent Na emission patterns, and also their potential relationship with the IMF variability. They found that the high latitude double peak is the most common Na emission pattern. Moreover, the lack of a statistically significant North–South asymmetry seems to disfavor the existence of an asymmetric and/or shifted intrinsic magnetic dipole. By analyzing a subset of quasi-full disk images, they found that the double peak Na emission is typically aligned along the meridian. Finally, the comparison with the IMF data seems to indicate that the contribution of the IMF BX component to the magnetic reconnection is generally weak.
①The Na exosphere of Mercury is being studied since its discovery in mid ‘80s from Earth-based telescopes, and it has revealed a high dynamics and variability. Although the processes and their relationships characterizing the Herman exosphere generation and dynamics are still not exhaustively understood, there are no doubts on a tight interconnection among the planet’s surface, exosphere, intrinsic magnetic field, the solar wind and the Interplanetary Magnetic Field (IMF). In this paper they analyze an extended dataset of images of the exospheric Na emission, collected from 2009 to 2013, by means of the THEMIS ground-based telescope, in order to perform a comprehensive statistical study of the recurrent Na emission patterns, and also their potential relationship with the IMF variability. They found that the high latitude double peak is the most common Na emission pattern. Moreover, the lack of a statistically significant North–South asymmetry seems to disfavor the existence of an asymmetric and/or shifted intrinsic magnetic dipole. By analyzing a subset of quasi-full disk images, they found that the double peak Na emission is typically aligned along the meridian. Finally, the comparison with the IMF data seems to indicate that the contribution of the IMF BX component to the magnetic reconnection is generally weak.
②They report the analysis of short-term ground-based observations of the exospheric Na emission (D1 and D2 lines) from Mercury, which was characterized by two high-latitude peaks confined near the magnetospheric cusp footprints. During a series of scheduled observations from the Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Solaires (THEMIS) telescope, achieved by scanning the whole planet, they implemented a series of extra measurements by recording the Na emission from a narrow north-south strip only, centered above the two emission peaks. Their aim was to inspect the existence of short-term variations, which were never analyzed before from ground-based observations, and their possible correlation with interplanetary magnetic field variations. Though Mercury possesses a miniature magnetosphere, characterized by fast reconnection events that develop on a timescale of few minutes, ground-based observations show that the exospheric Na emission pattern can be globally stable for a prolonged period (some days) and also exhibits fluctuations in the time range of tens of minutes.
