[PPS06-P08] Ground-based Observation of planetary lightning flashes by using Photomultiplier tube
Keywords:Venus, Lightning, Ground-based telescope, Photomultiplier tube, LAC
Our study’s purpose is to reveal the relationship between lightning and atmospheric dynamics. For this purpose, we develop the instrument to equip for the Pirka telescope. By using it, we observe Venus more than tens of hours to obtain the lightning’s light curve, occurrence frequency, and distribution. We reveal the relationship between lightning and atmosphere dynamics by comparing the lightning data and wind velocity and cloud distribution.
The Planetary Lightning Detector (PLD) we developed is designed for Venusian and Jovian lightning flashes' observation. From the previous study, the dominant wavelength of the lightning flashes could be 777 nm in Venus (Borucki et al.,1996). PLD equips narrowband filter (FWHM = 1nm) of 777 nm. PLD observes the light by using a Photomultiplier tube. The minimum exposure time is 50 microseconds. The maximum time resolution is about 2x104 points/s. PLD’s FOV can be changed to 5”, 10”, 30”, 60” pinhole and 2”x11” slit by using field stops. Slit and Pinhole are used for Venus’s night-side observation. To obtain the lightning’s light curve, we operate the bandpass filter to remove noise and large time scale variation by the atmosphere. And then, we search the large count value over 3-sigma. We have observed Venus by using PLD. For Venus’s data, we have obtained a few events whose count value is over the 3-sigma. These energies are estimated. The energy is about 109 to 1010 J. However, the light curves are too short less than 2 milliseconds and similar to the cosmic ray’s light curves obtained on different days. From this result, it’s considered we only observed the cosmic ray in this observation time. The observation time is not enough to reveal the lightning occurrence frequency for Venus. In the future, we increase the total observation time by using shorter exposure time.
In this presentation, we introduce the PLD and discuss the result observed from Jan 2020. And we report the plan of the cooperative observation with LAC (Lightning and Airglow Camera) onboard the AKATSUKI.