Spectral Characteristics of VLF Sferics Associated With RHESSI TGFs

Area of Science:

• Atmospheric physics
• Electromagnetism
• Radio science

Background:

• Terrestrial gamma-ray flashes (TGFs) are intense bursts of gamma rays produced by lightning.
• Very low frequency (VLF) radio emissions are associated with lightning and TGFs.
• Understanding the relationship between TGFs and VLF emissions is crucial for atmospheric physics.

Purpose of the Study:

• To compare modeled VLF radio emission spectral density from TGFs with simultaneously recorded VLF sferics.
• To investigate the influence of electron populations and TGF multiplicity on VLF emission characteristics.
• To determine if the number of seeding pulses in TGFs can be retrieved from VLF sferics.

Main Methods:

• Analysis of six TGF events with simultaneous VLF sferics recordings.
• Comparison of modeled and observed energy spectral densities in the VLF range.
• Investigation of spectral modulation due to TGF peak multiplicity.

Main Results:

• A good fit was observed between modeled and recorded VLF energy spectral densities.
• Secondary low-energy electrons dominate VLF spectral density, independent of relativistic electrons.
• TGF peak multiplicity influences VLF spectral shape, allowing retrieval of the number of seeding pulses.

Conclusions:

• The number of seeding pulses in TGFs can be estimated from VLF sferics.
• The number of seeding pulses ranges from approximately 10 to 10^3 for the studied events.
• VLF sferics provide valuable information about the source processes of TGFs.