Radio emissions from double RHESSI TGFs

TL;DR

This study analyzes RHESSI TGFs in relation to WWLLN and VLF data, revealing precise timing, simultaneous multi-peak correlations, and insights into the origins of VLF emissions during TGFs.

Contribution

It provides the first detailed timing analysis of RHESSI TGFs with WWLLN and VLF data, highlighting the potential to distinguish VLF emission mechanisms in double TGFs.

Findings

Clock offsets in RHESSI are stable within 100 μs.

WWLLN detects the last peak of multi-peak TGFs simultaneously.

VLF sferics are linked to the second TGF peak, not the first.

Abstract

A detailed analysis of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) terrestrial gamma ray flashes (TGFs) is performed in association with World Wide Lightning Location Network (WWLLN) sources and very low frequency (VLF) sferics recorded at Duke University. RHESSI clock offset is evaluated and found to experience changes on the 5 August 2005 and 21 October 2013, based on the analysis of TGF-WWLLN matches. The clock offsets were found for all three periods of observations with standard deviations less than 100 {\mu}s. This result opens the possibility for the precise comparative analyses of RHESSI TGFs with the other types of data (WWLLN, radio measurements, etc.) In case of multiple-peak TGFs, WWLLN detections are observed to be simultaneous with the last TGF peak for all 16 cases of multipeak RHESSI TGFs simultaneous with WWLLN sources. VLF magnetic field sferics were recorded for two of these 16 events at Duke University. These radio measurements also attribute VLF sferics to the second peak of the double TGFs, exhibiting no detectable radio emission during the first TGF peak. Possible scenarios explaining these observations are proposed. Double (multipeak) TGFs could help to distinguish between the VLF radio emission radiated by the recoil currents in the +IC leader channel and the VLF emission from the TGF producing electrons.