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1. Determining a lower limit of luminosity for the first satellite observation of a reverse beam terrestrial gamma-ray flash associated with a cloud to ground lightning leader

   https://doi.org/10.7291/d1gm4p  

   Chaffin, Jeffrey; Pu, Yunjiao; Smith, David; Cummer, Steve; Splitt, Mike; for_Particle_Physics, Santa_Cruz Institute (March 2023, Dryad)

   We provide an updated analysis of the gamma-ray signature of a terrestrial gamma ray flash (TGF) detected by the Fermi Gamma-ray Burst Monitor first reported by Pu et al. 2020. A TGF produced 3 ms prior to a negative cloud-to-ground return stroke was close to simultaneous with an isolated low frequency radio pulse during the leader’s propagation, with a polarity indicating downward moving negative charge. In prior observations this ‘slow’ low frequency signal has been strongly correlated with upward (opposite polarity) directed TGF events [Pu et al. 2019; Cummer et al. 2011]  leading the authors to conclude that the Fermi gamma ray observation is actually the result of a reverse positron beam generating upward directed gamma rays. We investigate the feasibility of this scenario and determine a lower limit on the luminosity of the downward TGF from the perspective of gamma-ray timing uncertainties, TGF Monte Carlo simulations, and meteorological analysis of a model storm cell and its possible charge structure altitudes. We determined the most likely source altitude of the reverse beam TGF to be 7.5 km +/- 2.6 km, just below an estimated negative charge center at 8 km. At that altitude the Monte Carlo simulations indicate a lower luminosity limit of 2 x 10^18 photons above 1 MeV for the main downward beam of the TGF making the reverse beam detectable by the Fermi Gamma Ray Burst Monitor. Geant4  Python  

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2. Determining a lower limit of luminosity for the first satellite observation of a reverse beam terrestrial gamma-ray flash associated with a cloud to ground lightning leader

   https://doi.org/10.5281/zenodo.7730674  

   Chaffin, Jeffrey; Pu, Yunjiao; Smith, David; Cummer, Steve; Splitt, Mike (March 2023, Zenodo)

   We provide an updated analysis of the gamma-ray signature of a terrestrial gamma ray flash (TGF) detected by the Fermi Gamma-ray Burst Monitor first reported by Pu et al. 2020. A TGF produced 3 ms prior to a negative cloud-to-ground return stroke was close to simultaneous with an isolated low frequency radio pulse during the leader's propagation, with a polarity indicating downward moving negative charge. In prior observations this 'slow' low frequency signal has been strongly correlated with upward (opposite polarity) directed TGF events [Pu et al. 2019; Cummer et al. 2011] leading the authors to conclude that the Fermi gamma ray observation is actually the result of a reverse positron beam generating upward directed gamma rays. We investigate the feasibility of this scenario and determine a lower limit on the luminosity of the downward TGF from the perspective of gamma-ray timing uncertainties, TGF Monte Carlo simulations, and meteorological analysis of a model storm cell and its possible charge structure altitudes. We determined the most likely source altitude of the reverse beam TGF to be 7.5 km +/- 2.6 km, just below an estimated negative charge center at 8 km. At that altitude the Monte Carlo simulations indicate a lower luminosity limit of 2 x 10^18 photons above 1 MeV for the main downward beam of the TGF making the reverse beam detectable by the Fermi Gamma Ray Burst Monitor. Geant4 Python Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: AGS-193598 

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3. Mountaintop Gamma Ray Observations of Three Terrestrial Gamma‐Ray Flashes at the Säntis Tower, Switzerland With Coincident Radio Waveforms

   https://doi.org/10.1029/2023JD039761  

   Chaffin, Jeffrey M.; Smith, David M.; Lapierre, Jeff; Cummer, Steve; Ortberg, John; Sunjerga, Antonio; Mostajabi, Amirhossein; Rubinstein, Marcos; Rachidi, Farhad (January 2024, Journal of Geophysical Research: Atmospheres)

   Abstract We report on the mountain top observation of three terrestrial gamma‐ray flashes (TGFs) that occurred during the summer storm season of 2021. To our knowledge, these are the first TGFs observed in a mountaintop environment and the first published European TGFs observed from the ground. A gamma‐ray sensitive detector was located at the base of the Säntis Tower in Switzerland and observed three unique TGF events with coincident radio sferic data characteristic of TGFs seen from space. We will show an example of a “slow pulse” radio signature (Cummer et al., 2011,https://doi.org/10.1029/2011GL048099; Lu et al., 2011,https://doi.org/10.1029/2010JA016141; Pu et al., 2019,https://doi.org/10.1029/2019GL082743; Pu et al., 2020,https://doi.org/10.1029/2020GL089427), a −EIP (Lyu et al., 2016,https://doi.org/10.1002/2016GL070154; Lyu et al., 2021,https://doi.org/10.1029/2021GL093627; Wada et al., 2020,https://doi.org/10.1029/2019JD031730), and a double peak TGF associated with an extraordinarily powerful and complicated positive‐polarity sferic, where each TGF peak is possibly preceded by a short burst of stepped leader emission. 

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4. Analysis of Paleointensity Results Under Different Interpretation Approaches: A Case Study on the Korkhi Volcanic Sequence (Lesser Caucasus, Georgia)

   https://doi.org/10.1029/2023GC011382  

   Sánchez‐Moreno, Elisa M; Calvo‐Rathert, Manuel; Goguitchaichvili, Avto; Vashakidze, George T; Tauxe, Lisa; Camps, Pierre; Morales‐Contreras, Juan; Lebedev, Vladimir A; Vegas, Néstor; Pérez‐Rodriguez, Nayeli; et al (April 2025, Geochemistry, Geophysics, Geosystems)

   Abstract In this study we focus on the investigation of the absolute intensity records of two volcanic subsequences, aiming to enrich the global paleointensity database for the last 5 Ma, which currently shows important dispersion. We present new absolute paleointensities obtained from the Plio‐Pleistocene volcanic sequence of Korkhi (Djavakheti Highland, Georgia) (41°27′31″N, 43°27′55″E). Korkhi is divided into two lava flow subsequences dated at 3.11 ± 0.20 Ma and 1.85 ± 0.08 Ma. Paleomagnetic directions previously published (Sánchez‐Moreno et al., 2018,https://doi.org/10.1029/2017GC007358) show a normal polarity in the lower Korkhi subsequence and a reverse‐to‐intermediate polarity in the upper Korkhi subsequence. The new paleointensity determinations are obtained through two different Thellier‐type protocols (Thellier‐Thellier and IZZI) and the corrected multispecimen method. We utilize different selection criteria and interpretation approaches (TTB, CCRIT, BiCEP and multimethod), and we make a critical evaluation on their application on complex magnetic behaviors, such as often found in volcanic rocks. Finally, we obtained a paleointensity of 70 μT in upper Korkhi and 14 paleointensities in lower Korkhi that vary between 5.2 and 37.2 μT. These results agree with a recently proposed non‐Geocentric Axial Dipole (GAD) hypothesis for the last ∼1.5 Ma (Cych et al., 2023,https://doi.org/10.1029/2023JB026492), and with low field strength for the 3–4 Ma. 

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5. Commentary on Paper by Matoza et al. (2021): Catalog Revision to a Common Depth Datum

   https://doi.org/10.1029/2025EA004754  

   Matoza, Robin S; Shearer, Peter M; Chang, Jefferson C; Okubo, Paul G (October 2025, Earth and Space Science)

   Abstract We present a revision and update to the high‐precision relocated seismicity catalog presented by Matoza et al. (2021,https://doi.org/10.1029/2020ea001253) for the Island of Hawai'i from 1986 to 2018. The starting catalog of hypocenters (input data), on which the study by Matoza et al. (2021,https://doi.org/10.1029/2020ea001253) was based, contained an inconsistent depth datum for events before and after 00:00 UT, 29 December 2017. Here we present a recomputed version of the catalog using a consistent reference depth. We corrected the starting catalog to a common depth datum (all events now use the model depth reference datum) and re‐ran the entire workflow as described in the paper by Matoza et al. (2021,https://doi.org/10.1029/2020ea001253). This included pairing, cross‐correlating, and relocating all seismic events again based on the updated starting catalog. We consider 347,446 events representing 32 years of seismicity on and around the island from 1986 to 2018. We now successfully relocate 299,966 (86%) events using ∼2.53 billion differential times (PandS) from ∼194 million similar‐event pairs, derived from cross‐correlations between ∼887 million event pairs total, a significant increase from our original analysis. The resolution of fine‐scale seismicity features is improved and the median depth of shallow events (<5 km) under Kaluapele (Kīlauea summit caldera) in 2018 is shifted 926 m deeper as a result of the change. The interpretations and other major conclusions in the paper by Matoza et al. (2021,https://doi.org/10.1029/2020ea001253) are unchanged. 

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