PPARCセミナー (2025/05/19)
PPARCセミナー (2025/05/19)
(1)
[Name]
Haruto Yamanaka
[Title]
Geotail衛星データを用いたAuroral Kilometric Radiationの長期統計解析:自動検出技術の適用
Long-term Statistical Analysis of Auroral Kilometric Radiation Observed by Geotail : Applied Automated Detection Technique
[Abstract]
Auroral Kilometric Radiation (AKR) is the strongest radio emission from Earth, generated by cyclotron resonance of energetic electrons along auroral magnetic field lines. Its intensity and frequency reflect electron acceleration processes, making it a valuable diagnostic for auroral dynamics.
We aim to conduct a long-term statistical analysis of AKR over multiple solar cycles, using data from the Geotail satellite. To remove overlapping Solar Type-III bursts, we adopt an automatic detection method originally developed for Wind. Given the differences in instrument configuration and sampling, we propose a hybrid thresholding method based on standard deviation, frequency variation, and temporal continuity.
At present, this method has demonstrated effectiveness in suppressing Solar Type-III interference, thereby enabling robust statistical analysis of AKR characteristics, including seasonal dependence, local time distribution, and correlations with solar activity. In this presentation, we detail the proposed automatic detection methodology and report on the current progress in our statistical investigation of AKR.
(2)
[Name]
Masamichi Waga
[Title]
Analysis of spatial structure of electrons in the Jupiter’s radiation belts using GMRT : Coordinated observations with Juno
[Abstract]
Jupiter’s synchrotron radiation (JSR) is emitted from the relativistic electrons trapped in the Jupiter’s radiation belts. Its intensity and frequency depend on electron energy, electron number density, and magnetic field strength. Therefore, radio observations of JSR are the most effective probes for studying the spatial structure and dynamics of radiation belts. One of the dominant physical processes in the Jovian magnetosphere is electron loss caused by the sweeping effect of the Jovian moons (Amalthea and Thebe) orbiting inside the radiation belts. As electrons diffuse inward, substantial populations of electrons are lost owing to collisions with the moons. The electron loss due to the sweeping effect strongly depends on the electron energy and pitch angle (angle of the electron velocity vector with respect to the local magnetic field). As a result, a difference in the electron energy is expected between lower pitch angle electrons, which contribute to the radiation at high-latitude and higher pitch angle electrons near the equator. However, this energy dependence has not yet been demonstrated by observation.
We conducted simultaneous cooperative observations with radio interferometers, including Giant Metre Wave Radio Telescope (GMRT) in India, and single telescopes in Japan (Iitate and Usuda) at the time of Juno’s perijove (PJ66) on 23 October 2024. Juno is currently on a trajectory that passes through the radiation belts, providing a valuable opportunity to obtain information on the electron distribution based on the in-situ measurement. On the other hand, ground-based radio observations play an important complementary role to Juno. While Juno’s in-situ observations are not able to provide a complete spatial distribution of the radiation belts, two-dimensional radio maps of JSR can provide a complete picture of the spatial distribution. In addition, multi-frequency observations can estimate the energy spectrum of the electrons, which is expected to improve the physics model of the radiation belts.
We observed JSR by GMRT in two frequency bandwidths, Band 2 (125-150 MHz) on 21-22 October 2024 and Band 4 (550-900 MHz) on 22-23 October 2024. As part of the multi-frequency observation campaign, we analyzed the GMRT Band 4 data using an analysis method called Source Peeling and Atmospheric Modeling (SPAM), which calibrates propagation delays caused by the terrestrial ionosphere. As a result, we succeeded in producing high-resolution radio images that spatially separate high-latitude and equatorial radiation.
In this paper, we present the results of the radiation belts images from GMRT observations and discuss the spatial structure of electrons in the radiation belts.
