15:30 〜 15:45
[PPS05-01] Observation of Venus lightning by two photomultiplier tubes mounted on a 1.6-m ground-based telescope
キーワード：金星、雷、地上望遠鏡、光電子増倍管
The lightning activity and distribution can be used to reveal the mechanism of atmospheric dynamics on the other planets. The convection generates lightning in the atmosphere. Lightning has been detected by spacecraft through night-side optical imaging and radio wave observation on Jupiter. Previous studies (Gierash et al., 2000; Ingersoll et al., 2000) suggested that the many small-scale eddies, receiving their energy from the moist convection that generates the lightning, drive the zonal jet. Moist convection is expected to be correlated with the jovian lightning distribution, like as on Earth. LAC onboard AKATSUKI recorded a possible optical signal from Venusian lightning on March 1, 2020 (Takahashi et al., 2020). If the signal is originated by lightning discharge, the occurrence rate is equal to 2.7x1012 s-1km-2 reported by Hansell et al., 1995. If we can monitor global Venusian lightning activity and distribution continuously, it could be helpful to investigate the Venusian atmospheric dynamics.
We have developed the Planetary lightning Detector (PLD) to observe the optical Jovian and Venusian lightning flashes and be installed on a 1.6-m Pirka ground-based telescope. The PLD is a high-speed photon-counting sensor using the photomultiplier tube to obtain the light curve of lightning optical flashes. The sampling rate is over 20 s-1. PLD observes the background level simultaneously with another photomultiplier tube with a broadband filter to ensure the light detected at the lightning emission line is well over the noise level. We use a beamsplitter to separate the incident light from the telescope into two photomultiplier tubes. The first photomultiplier tube observes the wavelength of Jovian or Venusian lightning. The PLD is equipped with narrowband filters of 777 nm (FWHM = 1nm) for Venusian lightning and 656 nm (FWHM = 1nm) for Jovian lightning (Borucki et al., 1996). The second photomultiplier tube observes the background variation. The wavelength of the broadband filter is 740 nm (FWHM = 10 nm) for recording the background variations. We have observed Venus and Jupiter since 2021. We analyze the data with wavelet denoising to remove the pulses caused by cosmic rays and shot noise. We compare the light curve obtained by the first PMT and the background variation observed by the second PMT after denoised. If a waveform showing an increase in value is observed in the first PMT, unlike the second PMT, and the pulses have a larger count value above four sigmas of the background noise amplitude, the candidate pulses are considered to have been detected. In the case of Venus, several possible pulses are found. We can’t rule out the possibility that all recorded light curve is generated by noise. We need to discuss statistically and precisely such as signal-to-noise ratio to conclude the detection the lightning by increasing the total observation time. We are going to observe Venus as much as possible until conjunction in 2022.
In this time, we will introduce the developed lightning observation instrument PLD, the analysis method, and present our observation results obtained from 2021.
We have developed the Planetary lightning Detector (PLD) to observe the optical Jovian and Venusian lightning flashes and be installed on a 1.6-m Pirka ground-based telescope. The PLD is a high-speed photon-counting sensor using the photomultiplier tube to obtain the light curve of lightning optical flashes. The sampling rate is over 20 s-1. PLD observes the background level simultaneously with another photomultiplier tube with a broadband filter to ensure the light detected at the lightning emission line is well over the noise level. We use a beamsplitter to separate the incident light from the telescope into two photomultiplier tubes. The first photomultiplier tube observes the wavelength of Jovian or Venusian lightning. The PLD is equipped with narrowband filters of 777 nm (FWHM = 1nm) for Venusian lightning and 656 nm (FWHM = 1nm) for Jovian lightning (Borucki et al., 1996). The second photomultiplier tube observes the background variation. The wavelength of the broadband filter is 740 nm (FWHM = 10 nm) for recording the background variations. We have observed Venus and Jupiter since 2021. We analyze the data with wavelet denoising to remove the pulses caused by cosmic rays and shot noise. We compare the light curve obtained by the first PMT and the background variation observed by the second PMT after denoised. If a waveform showing an increase in value is observed in the first PMT, unlike the second PMT, and the pulses have a larger count value above four sigmas of the background noise amplitude, the candidate pulses are considered to have been detected. In the case of Venus, several possible pulses are found. We can’t rule out the possibility that all recorded light curve is generated by noise. We need to discuss statistically and precisely such as signal-to-noise ratio to conclude the detection the lightning by increasing the total observation time. We are going to observe Venus as much as possible until conjunction in 2022.
In this time, we will introduce the developed lightning observation instrument PLD, the analysis method, and present our observation results obtained from 2021.