Presentation Information
[PPS01-P11]Variability characteristics of Jupiter's narrowband kilometric radioation (nKOM)
Rentaro Sugawara1, *Hiroaki Misawa1, Fuminori Tsuchiya1, Rikuto Yasuda1 (1.Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University)
Keywords:
Jupiter,narrow band kilometric radiation,JUNO Jupiter orbitor,magnetospheric variation
This study focused on narrowband Kilometric Radiation (nKOM) emitted from the outer edge of the Io plasma torus as an indicator reflecting variations in magnetospheric dynamics. No quantitative understanding had been obtained regarding how nKOM's appearance characteristics relate to changes in the internal environment (plasma supply) and changes in the external environment (solar wind). Therefore, this study utilizes long-term continuous observation data acquired from July 2016 to February 2020 (Perijove 1–25) by the WAVES and JADE instruments onboard the JUNO Jupiter orbiter. Based on the creation and establishment of a detailed database of nKOM occurrences, we performed statistical analyses on the occurrence characteristics of nKOM and their variation factors.
The analysis yielded three major findings regarding the nKOM variation mechanism. First, concerning internal factors: a statistically significant positive correlation was confirmed between the heavy ion density within the magnetospheric plasmasheet and the nKOM occurrence rate. This result supports the scenario, previously proposed for phenomena like polar auroras, where increased plasma supply originating from Io's volcanic activity enhances plasma accumulation in the magnetosphere, thereby increasing the frequency of large-scale magnetospheric disturbances caused by magnetic reconnection. Second, regarding the relationship with external factors. Analysis of the relationship between solar wind kinetic pressure at Jupiter's position (predicted by the so-called Tao model) and nKOM intensity revealed a tendency for radiation intensity to increase with rising solar wind kinetic pressure under conditions of high plasma density within the magnetosphere. However, further scrutiny is needed to confirm the validity of this finding. This suggests that solar wind-induced magnetospheric compression plays a role in amplifying the radiated energy of nKOM. Third, the evaluation and confirmation of observational bias. A "negative correlation" was observed, where the apparent occurrence rate of nKOM decreased during periods of high solar wind dynamic pressure. Detailed spectral analysis revealed this was not an actual suppression, but rather a "masking effect" where broadband kilometer-wave radio (bKOM) signals, activated by the solar wind, obscured the nKOM frequency band. This finding is essential for correctly evaluating the influence of the solar wind.
The analysis yielded three major findings regarding the nKOM variation mechanism. First, concerning internal factors: a statistically significant positive correlation was confirmed between the heavy ion density within the magnetospheric plasmasheet and the nKOM occurrence rate. This result supports the scenario, previously proposed for phenomena like polar auroras, where increased plasma supply originating from Io's volcanic activity enhances plasma accumulation in the magnetosphere, thereby increasing the frequency of large-scale magnetospheric disturbances caused by magnetic reconnection. Second, regarding the relationship with external factors. Analysis of the relationship between solar wind kinetic pressure at Jupiter's position (predicted by the so-called Tao model) and nKOM intensity revealed a tendency for radiation intensity to increase with rising solar wind kinetic pressure under conditions of high plasma density within the magnetosphere. However, further scrutiny is needed to confirm the validity of this finding. This suggests that solar wind-induced magnetospheric compression plays a role in amplifying the radiated energy of nKOM. Third, the evaluation and confirmation of observational bias. A "negative correlation" was observed, where the apparent occurrence rate of nKOM decreased during periods of high solar wind dynamic pressure. Detailed spectral analysis revealed this was not an actual suppression, but rather a "masking effect" where broadband kilometer-wave radio (bKOM) signals, activated by the solar wind, obscured the nKOM frequency band. This finding is essential for correctly evaluating the influence of the solar wind.