Relativistic electron avalanches as a thunderstorm discharge competing with lightning

Nicole A Kelley,Forest Martinez-Mckinney,Joseph R Dwyer,Alexander Lowell,Michael Splitt,Steven Lazarus,Hamid K Rassoul,Bryna Hazelton,Brian Grefenstette,David M Smith

doi:10.1038/ncomms8845

Abstract

Gamma-ray 'glows' are long duration (seconds to tens of minutes) X-ray and gamma-ray emission coming from thunderclouds. Measurements suggest the presence of relativistic runaway electron avalanches (RREA), the same process underlying terrestrial gamma-ray flashes. Here we demonstrate that glows are relatively a common phenomena near the tops of thunderstorms, when compared with events such as terrestrial gamma-ray flashes. Examining the strongest glow measured by the airborne detector for energetic emissions, we show that this glow is measured near the end of a downward RREA, consistent with occurring between the upper positive charge layer and the negative screening layer above it. The glow discharges the upper positive layer by ≥9.6 mA, strong enough to be an important charging mechanism of the storm. For this glow, the gamma-ray flux observed is close to the value at which relativistic feedback processes become important, with an avalanche multiplication factor of 4,500.

Highlights

Gamma-ray ‘glows’ are long duration X-ray and gamma-ray emission coming from thunderclouds
The relativistic runaway electron avalanche (RREA) process was first proposed by Gurevich et al.[1] to help explain the large flux of gamma rays seen by McCarthy and Parks[2] in 1983 aboard a NASA F-106 airplane during a thunderstorm
The relativistic feedback process builds on the relativistic runaway electron avalanches (RREA) process by including the physics of backscattered gamma rays and positrons from gamma-ray pair production, both of which propagate to the start of the avalanche region and generate new avalanches, producing an exponential growth in the number of avalanches

Summary

Introduction

Gamma-ray ‘glows’ are long duration (seconds to tens of minutes) X-ray and gamma-ray emission coming from thunderclouds. The glow discharges the upper positive layer by Z9.6 mA, strong enough to be an important charging mechanism of the storm For this glow, the gamma-ray flux observed is close to the value at which relativistic feedback processes become important, with an avalanche multiplication factor of 4,500. The relativistic runaway electron avalanche (RREA) process was first proposed by Gurevich et al.[1] to help explain the large flux of gamma rays seen by McCarthy and Parks[2] in 1983 aboard a NASA F-106 airplane during a thunderstorm. RREA and glows may produce a significant discharge current, which can balance the charging of the cloud, with the bulk of the current coming from molecules ionized by the relativistic particle, not the energetic electrons directly[18]. We demonstrate for the first time that glows can provide a comparably effective channel to lightning for thunderstorm discharge

Methods

Results

Conclusion