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

Abstract

We 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.

Time Evolution of Storms Producing Terrestrial Gamma-Ray Flashes Using ERA5 Reanalysis Data, GPS, Lightning and Geostationary Satellite Observations

“…It is important to underline that the peak over Africa, where the electrical activity manifests its distribution peaks on Earth, results as underestimated due to the lower amount of coverage by WWLLN sensors that make the recording of lightning activity difficult. The local time distribution shows a higher rate of events occurring in the early morning as well as in the late afternoon according to [23]. The duration of TGFs, expressed as the t50 parameter, shows a peak at 20-40 µs, consistent with the observations by [28] regarding TGFs with a lightning sferics simultaneous association, confirming the higher WWLLN matches chance with brief TGF durations [22,28].…”

“…Additional information on MCAL performances is included in [23,25,26]. Additional information on the association between TGF data and lightning data is included in [22].…”

“…We analyzed a total of 648 TGFs with an associated lightning sferic from March 2015 to February 2020 detected from the AGILE MCAL instrument, representing an extension of the 3rd AGILE catalog (282 TGFs in the period 2015-2018 [23] (see Figures 1 and 2). In particular, the TGF sample was identified by the association criteria with radio sferics, detected by the WWLLN network [27], which are described in [22].…”

“…The scope is to understand which conditions are favorable to the development of TGF events and to investigate if any precursor signals can be expected. To do that, TGFs from the AGILE satellite [21][22][23] were considered. The first meteorological conditions in correspondence with TGF occurrences were studied by ERA5 reanalysis and compared with reference values, in order to evaluate the meteorological conditions leading to storms emitting TGFs.…”

The 3rd AGILE Terrestrial Gamma Ray Flash Catalog. Part I: Association to Lightning Sferics

“…Therefore, a WWLLN identified (WI) TGF sample can make the basis for deciding appropriate new SC to identify TGFs without associated WWLLN detections. These new SC are discussed in the companion paper by Maiorana et al (2020), hereafter referred to as M20.…”