Hardening and termination of long-duration gamma rays detected prior to lightning

TL;DR

This study reports the first observation of prolonged gamma-ray emission prior to lightning, which abruptly terminates just before the lightning flash, providing insights into the connection between gamma-ray activity and lightning initiation.

Contribution

It presents the first direct observation of gamma-ray hardening and termination before lightning, revealing the spatial and temporal characteristics of gamma-ray emission related to lightning.

Findings

Gamma-ray emission lasted less than 3 minutes and hardened before lightning.

Gamma-ray flux abruptly ceased less than 800 ms before lightning.

Higher-energy gamma rays (>10 MeV) had a smaller emission area than lower-energy gamma rays.

Abstract

We report the first observation of 3$-$30 MeV prolonged gamma-ray emission that was abruptly terminated by lightning. The gamma-ray detection was made during winter thunderstorms on December 30, 2010 by the Gamma-Ray Observation of Winter THunderclouds (GROWTH) experiment carried out in a coastal area along the Sea of Japan. The gamma-ray flux lasted for less than 3 min, continuously hardening closer to the lightning occurrence. The hardening at energies of 3$-$10 MeV energies was most prominent. The gamma-ray flux abruptly ceased less than 800 ms before the lightning flash that occurred over 5 km away from the experimental site. In addition, we observed a clear difference in the duration of the 3$-$10 MeV gamma rays and those $>$10 MeV, suggesting that the area of $>$10 MeV gamma-ray emission is considerably smaller than that of the lower-energy gamma rays. This work may give a manifestation that a local region emitting prolonged gamma rays connects with a distant region to initiate lightning.