Lightning-Triggered Termination of a Gamma-ray Glowin a Japanese Winter Thunderstorm (AE33A-3397)
Yuuki Wada (University of Tokyo / RIKEN : wada@juno.phys.s.u-tokyo.ac.jp)
G.S.Bowers, T.Enoto, M.Kamogawa, Y.Nakamura, T.Morimoto, D.M.Smith, Y.Furuta,
K.Nakazawa, T.Yuasa, A.Matsuki, M.Kubo, T.Tamagawa, K.Makishima, H.Tsuchiya
Published in Geophysical Research Letters (Wada et al. 2018; DOI: 10.1029/2018GL077784)

1. Introduction

2. Instruments

Thunderclouds produce minute-lasting emissions:gamma-ray glows / thunderstorm ground enhancements.

Observation site: Kanazawa University Noto School- GROWTH detector: 3-inch cylindrical BGO (Enoto+2017)- GODOT detector: 5-inch cylindrical NaI (Bowers+2017)- Atmospheric E-field monitor: Boltek EF-100

Bremsstrahlung of avalanche electrons in strong E-field.
Glows sometimes cease with a lightning discharge.
(e.g. McCarthy & Parks 1985, Tsuchiya+2013, Chilingarian+2017)

Fundamental questions of gamma-ray glows:- Life cycle, acceleration mechanisms, energetics- Do glows assist or prevent lightning initiations?

LF network to detect lightning discharges (0.8-500 kHz)- Lightning mapping with 5 stations (time-of-arrival).
GROWTHdetector

Sea of Japan
Peninsula(e.g. McCarthy & Parks 1985, Eack+1996, Kelley+2015, Chilingarian+2011)↑BGO

ee-> 3 km< 1 km

3. Results- Suitable target:
winter thunderstorms- Lower cloud bases allow us
to detect glows at sea level.

←GODOT
detector

LF receiver

LF stations
Google Map

We detected a gamma-ray glow on 11th February 2017
during heavy winter thunderstorms.
- The glow lasted for ~60 sec, with energies up to 20 MeV.

GROWTH detector
0.2-7.0 MeV

Before, during, after the glow, electric field was negative,indicating the cloud base was negatively charged.
GODOT detector
0.3-20.0 MeV

GROWTH

Lightning mapping

The glow ceased with a lightning discharge.
- Termination at 08:10:08.093 +/- 0.052 UTC(evaluated by fitting with a step function)discharge

E-field monitor

electronics

Observation
siteNotoWinterSummer50 km

LF network detected the lightning discharge.
- It continued to develop for ~300 ms,
spread ~70 km wide in east-west direction.
(one of winter lightning’s features)
The discharge passed above observation site.
- Six faint in-cloud pulses within 1 km.
- Timing of the passage is consistent withwhen the glow terminated.

Glowtermination

4. Discussion

5. Summary

The glow was terminated by pulses of an IC. - Winter thunderstorms are suitable
LF waveform- The pulses might make electric filed lower
for gamma-ray glow studies.
0.8-500 kHz
than the threshold for electron avalanche.
- We detected a glow terminated- Even small pulses can disturb the glow.
by an IC discharge.
Model 1Was the glow related to the lightning initiation?
- - -- - - - - The IC passed nearby the glow.
- No. The IC initiated 15 km west from the glow.
e- - - +++ - - +++--+++
Model 2-----e-+++--------++++++++

What is charge structure inside the thundercloud - The nearby pulses destroyed
E-field region for the glow.
responsible for the electron acceleration?
- E-field between cloud base and ground was too low. - E-field measurement suggests- Two possibilities:
two possible charge structures.
1. Traditional local positive charge region.
- The glow was not related
2. A charge pair above a negative charge layer.
to the lightning initiation.

AE33A-3397, Atmospheric and Space Electricity, 12 December 2018, American Geophysical Union Fall Meeting 2018 at Washington D.C.