The 3rd AGILE Terrestrial Gamma‐ray Flashes Catalog. Part II: Optimized Selection Criteria and Characteristics of the New Sample

C Maiorana,M Tavani,A Ursi,F Verrecchia,A Lindanger,D Sarria,M Marisaldi,C Labanti,N Østgaard,C Pittori,M Galli

doi:10.1029/2019jd031986

Abstract

AbstractWe present in this work the third catalog of terrestrial gamma‐ray flashes (TGFs) by the AGILE mission and the new search algorithm that was developed to produce it. We firstly introduce the new selection criteria, designed from the characteristics of WWLLN‐identified TGFs, and then applied on all data from March 2015 to September 2018. Association with sferics was performed by an independent search, described in a companion paper by Lindanger et al. (2020, https://doi.org/10.1029/2019JD031985). This search showed that many TGFs were not recognized by the existing selection algorithm, hence the need for this work. Several new selection criteria were tested and are compared in this paper. We then present the chosen selection criteria and the obtained sample, which includes 2,780 events and represents the most extensive TGF catalog available for the equatorial regions. Finally, we discuss the characteristics of this sample, including geographic distribution, intensity and duration, and seasonal variations.

Highlights

Terrestrial gamma-ray flashes (TGFs) are bursts of gamma photons produced inside thunderstorms and associated to lightning
We chose a 15-km altitude because it is an adequate value for cloud top altitude in equatorial thunderstorms, as well as a value compatible with the analysis reported in Dwyer and Smith (2005) and Hazelton et al (2009), lower altitudes have been reported for the lightning leaders involved in TGF production (Cummer et al, 2015) and from radar observations associated to TGFs (Chronis et al, 2016)
We count each cluster as a single event, regardless of its possible association with a multipulse event, as we are considering the efficiency of the criteria in selecting clusters

Summary

Introduction

Terrestrial gamma-ray flashes (TGFs) are bursts of gamma photons produced inside thunderstorms and associated to lightning They typically last for less than 1 ms, have energies up to a few tens of megaelectron volt, and are bright enough to be detected by particle detectors on spacecrafts. They were first recorded by the Burst and Transient Source Experiment (BATSE) instrument onboard the Compton Gamma Ray Observatory (CGRO) mission (Fishman et al, 1994), by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) (Smith et al, 2005). Each of these missions are observing a slightly different population, due to the intrinsic differences in the detectors and orbits

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