Radio emissions from double RHESSI TGFs

Area of Science:

• Space Physics
• Atmospheric Physics
• High-Energy Astrophysics

Background:

• Terrestrial gamma ray flashes (TGFs) are intense bursts of gamma rays produced during thunderstorms.
• The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has provided valuable data on TGFs.
• Understanding the precise timing and characteristics of TGFs is crucial for correlating them with other geophysical phenomena.

Purpose of the Study:

• To perform a detailed analysis of RHESSI TGFs in conjunction with World Wide Lightning Location Network (WWLLN) data and very low frequency (VLF) sferics.
• To evaluate and correct for RHESSI clock offsets to enable precise comparative analyses.
• To investigate the characteristics of multi-peak TGFs and their associated radio emissions.

Main Methods:

• Analysis of RHESSI TGF data matched with WWLLN sources.
• Evaluation of RHESSI clock offsets using TGF-WWLLN timing.
• Recording and analysis of VLF magnetic field sferics at Duke University for specific multi-peak TGF events.

Main Results:

• RHESSI clock offsets were identified and quantified for different observation periods, with standard deviations under 100 μs.
• For all 16 observed multi-peak TGFs coincident with WWLLN sources, the WWLLN detections occurred simultaneously with the last TGF peak.
• VLF sferics were predominantly associated with the second peak of double TGFs, with no detectable radio emission during the first peak.

Conclusions:

• The identified RHESSI clock offsets allow for accurate cross-correlation of TGF data with other measurements.
• The timing of multi-peak TGFs and their associated VLF emissions provide evidence for distinct physical processes occurring during different phases of the lightning discharge.
• These findings aid in differentiating VLF radio emission mechanisms, such as recoil currents in the +IC leader channel versus electron-driven emission in TGFs.