In-flight measurements of energetic radiation from lightning and thunderclouds

TL;DR

This study reports in-flight measurements of x-ray emissions from lightning strikes on aircraft, correlating x-ray bursts with lightning processes to better understand lightning physics and potential radiation exposure during flights.

Contribution

The paper introduces in-situ x-ray detection during aircraft lightning strikes, linking x-ray emissions with lightning processes and providing new insights into lightning physics and radiation safety.

Findings

X-ray bursts are synchronized with lightning leader steps.

X-ray energies reach up to 10 MeV.

X-ray emissions are associated with specific lightning processes.

Abstract

In the certification procedure aircraft builders carry out so-called icing tests flights, where the zero degree Celsius altitude is deliberately sought and crossed in or under thunderstorms. Airbus also used these flights to test ILDAS, a system aimed to determine lightning severity and attachment points during flight from high speed data on the electric and magnetic field at the aircraft surface. We used this unique opportunity to enhance the ILDAS systems with two x-ray detectors coupled to high speed data recorders in an attempt to determine the x-rays produced by lightning in-situ, with synchronous determination of the lightning current distribution and electric field at the aircraft. Such data are of interest in a study of lightning physics. In addition, the data may provide clues to the x-ray dose for personnel and equipment during flights. The icing campaign ran in April 2014; in six flights we collected data of 61 lightning strikes on an Airbus test aircraft. In this communication we briefly describe ILDAS and present selected results on three strikes, two aircraft initiated and one intercepted. Most of the x-rays have been observed synchronous with initiating negative leader steps, and as bursts immediately preceding the current of the recoil process. Those processes include the return stroke. The bursts last one to four micro-second and attain x-ray energies up to 10 MeV. Intensity and spectral distribution of the x-rays and the association with the current distribution are discussed. ILDAS also continuously records x-rays at low resolution in time and amplitude.