Major brightening events in Jupiter's sodium nebula during Juno era

Successive observations of Jupiter's sodium nebula have identified several brightening events, presumably due to variability in Io's volcanic plumes. An event that began in the beginning of March 2018 has been already reported by Morgenthaler et al. (2019,2024a,2024b). In this work, we found that this event was followed by another one. By adding these observations, details of these events including one observed by Morgenthaler et al. (2019,2024a,2024b) are described herein. Especially, the event in 2018 seems to have been the strongest enhancement during Juno spacecraft's orbital mission, at least before 2020. Also, our observations show that the D-line brightness of the sodium nebula was decreasing in early September, 2019. This tendency is consistent with Io's volcanic plume activity observed by Atacama Large (sub)Millimeter Array (ALMA). The KCl gas observed in this plume with ALMA is a chemical analog of NaCl, which is believed to be the parent molecule that dissociates to form the sodium nebula. While these observations are not the direct evidence of plume supply to sodium nebula, they are suggestive of control of Io's volcanic plumes on the brightness of Jupiter's sodium nebula.