Observation of lightning optical emission with photometer installed on ground-based telescope

The monitoring of lightning can be used to understand the atmospheric dynamics on the other planets. The lighting is generated by the convection in the planetary atmosphere. Jovian lightning has been detected by spacecraft through night-side optical imaging and global radio wave observation. Previous studies (Gierasch et al., 2000; Ingersoll et al., 2000) suggested that zonal jet is driven by the many small-scale eddies receiving their energy from the moist convection that generates the lightning. Moist convection is expected to be correlated with the lightning distribution on Jupiter, like as on Earth. In Venus, LAC onboard AKATSUKI recorded a possible optical signal on March 1, 2020 (Takahashi et al., 2020). If the flash is generated by lightning discharge, the occurrence rate is almost equal to 2.7x10-12 [s-1km-2] reported by Hansell et al., 1995. If we can monitor Venusian lightning globally and continuously, it could be useful to examine the Venusian atmospheric dynamics. We have developed the Planetary lightning Detector (PLD) to observe the optical planetary lightning flashes, especially for Jupiter and Venus, to be installed on a 1.6-m Pirka ground-based telescope. The PLD is a high-speed and high-sensitive photon-counting sensor using the photomultiplier tube to obtain the light curve of lightning optical flashes at a sampling rate of over 20 s-1. The PLD is equipped with narrowband filters of 777 nm (FWHM = 1nm) and 656 nm (FWHM = 1nm) for Jovian and Venusian lightning (Borucki et al., 1996), respectively. We have observed Venus and Jupiter since the month of 2020. We analyze the data with wavelet denoising to remove the shot noise and pulses caused by cosmic rays. In the very preliminary analysis for Venus, several possible pulses are found. The pulses have a larger count value above four sigmas of the background level. The estimated time-integrated energy of the optical flash ranges from 106 to 108 J. We cant 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. To ensure the light detected at the lightning emission line is well over the noise level, PLD observes the background level simultaneously with another photomultiplier tube with a broadband filter since the month of 2021.