[P-PS04] Recent advances in the science of Venus

[PPS04-P07] Development of Venusian Lightning model for observation of PLD based on JEM-GLIMS measurement of Earth lightning

*大野 辰遼¹、高橋 幸弘¹、佐藤 光輝²、高木 聖子²、今井 正尭³ (1.北海道大学・大学院理学院・宇宙理学専攻、2.北海道大学 大学院理学研究院、3.東京大学)

キーワード：金星、雷、地上望遠鏡、モデル開発

Lightning is an electrical phenomenon composed of electric discharge through the atmosphere. It occurs not only on Earth but also on planets like Jupiter and Venus. Some previous observations with ground-based telescopes or probes detected the possible signal originating from Venusian lightning. LAC onboard AKATSUKI triggered a potential signal on March 1, 2020 (Takahashi et al., 2020). If the lightning discharge is the signal source, the occurrence rate equals the estimated by the ground-based telescope observation (Hansell et al., 1995). Lightning could help reveal the Venusian atmospheric dynamics. Lightning activity has correlated with atmospheric activity because moist convection would be one of the generation mechanisms for lightning discharge in dense clouds. However, several issues prevent us from understanding Venusian lightning, such as its existence, mechanism, and distribution due to the monitoring time deficit. We have developed the Planetary Lightning Detector (PLD) for the 1.6-m ground-based telescope to enable us to achieve high-frequency monitoring observations. Using two-band simultaneous photon counting, PLD can distinguish between the lightning and the contamination caused by the other light sources. The first photomultiplier tube observes the wavelength of Venusian lightning with 777 nm (FWHM = 1nm). The second photomultiplier tube simultaneously observes the background variation with the broadband filter with 700 nm (FWHM = 10 nm). If a considerable count value above the trigger level estimated by the noise amplitude was detected on the PMT's signal of 777 nm only, unlike the second PMT, the candidate waveform has been detected. From the data of observing Venus since 2021, we triggered several possible signals. We cannot rule out the possibility that all recorded light curves originate from noise or Cosmic rays. It is disputable to conclude that we have detected lightning. We compare it with our developing model and the Earth lightning light curve observed by JEM-GLIMS to test if the observed lightning is possible.