The Temporal Relationship Between Terrestrial Gamma-Ray Flashes and Associated Optical Pulses From Lightning

Area of Science:

• Atmospheric physics
• Space science
• High-energy astrophysics

Background:

• Terrestrial Gamma-ray Flashes (TGFs) are brief, intense bursts of gamma rays originating from thunderstorms.
• Understanding the relationship between TGFs and optical emissions is crucial for comprehending lightning processes.

Purpose of the Study:

• To investigate the temporal relationship between TGFs and associated optical pulses observed by the ASIM instrument.
• To categorize TGF events based on their duration and the delay between TGF and optical pulse onsets.

Main Methods:

• Analysis of 221 TGF events detected by the Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station.
• Utilizing X- and gamma-ray energy detections, photometer data (180-230, 337, 777 nm), and optical camera data (337, 777 nm).
• Cross-referencing TGF characteristics and lightning detections to determine event association and location relative to the ASIM photometer's field of view.

Main Results:

• 72 out of 221 events showed clear association between TGFs and optical pulses within the photometer's field of view.
• TGF onsets consistently occurred before or simultaneously with optical pulse onsets, accounting for cloud scattering effects.
• A correlation was observed between longer TGF durations and increased delays in optical pulse onsets.
• Two distinct event groups emerged: one with potential overlap between TGF and optical emissions, and another with significant delays unexplainable by cloud scattering.

Conclusions:

• TGFs and associated optical emissions exhibit complex temporal relationships.
• The observed delays and durations suggest at least two different mechanisms may be responsible for generating TGFs and their optical counterparts.
• Further research is needed to fully elucidate the interplay between high-energy atmospheric phenomena and visible light emissions during thunderstorms.