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1. 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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2. Photoelectric Effect in Air Explains Lightning Initiation and Terrestrial Gamma Ray Flashes

   https://doi.org/10.1029/2025JD043897  

   Pasko, Victor P; Celestin, Sebastien; Bourdon, Anne; Janalizadeh, Reza; Pervez, Zaid; Jansky, Jaroslav; Gourbin, Pierre (July 2025, Journal of Geophysical Research: Atmospheres)

   Abstract Terrestrial gamma ray flashes (TGFs) are high‐energy photon bursts that have been linked to short bursts of electromagnetic radiation associated with lightning activity. The most puzzling unexplained aspect of these events is that gamma rays originate from very compact regions of space while the source regions often seem to be optically dim and radio silent when compared to processes in ordinary lightning discharges. In this work, we report a mechanism that allows precise quantitative explanation of these peculiar features of TGFs and their relationships to the observed waveform characteristics of associated radio emissions. The mechanism represents an extension of earlier ideas on feedback processes in growth of relativistic runaway electron avalanches (Dwyer, 2003,https://doi.org/10.1029/2003GL017781), and is based on a recent demonstration of the dominant role of the photoelectric feedback on compact spatial scales (Pasko, Celestin, et al., 2023,https://doi.org/10.1029/2022GL102710). Since discussed events often occur in isolation or precede formation of lightning discharges, the reported findings propose a straightforward solution for the long‐standing problem of lightning initiation. 

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3. Turbulent Heating in Jupiter's Middle Magnetosphere From Juno Data

   https://doi.org/10.1029/2026JA035351  

   Franciscovich, M T; Ng, C S; Delamere, P A; Damiano, P A; Spitler, C E; Smith, A R; Palmer, V A (July 2026, Journal of Geophysical Research: Space Physics)

   Abstract The ion temperature in Jupiter's middle magnetosphere has been known to stay constant (or even increase) as a function of radial distance from the planet. This suggests that there is a non‐adiabatic heating process occurring in this region. Efforts have been made to explain this heating with different turbulent heating models utilizing data from previous science missions to Jupiter (Ng et al., 2018,https://doi.org/10.1029/2018JA025345; 2022,https://doi.org/10.1029/2021GL096662; Saur, 2004,https://doi.org/10.1086/382588). Using the turbulent heating rate density calculated from the Juno spacecraft magnetometer and particle data based on a forward fitting model utilizing a kappa distribution (Wang, Bagenal, Wilson, Nerney, et al., 2024,https://doi.org/10.1029/2023JA032218; Wang et al., 2024b,https://doi.org/10.1029/2024JA033454), the thermal equilibrium ion temperature in Jupiter's middle magnetosphere is estimated using an advection temperature model. We find that the model is not sufficient to account for the – K ( keV) temperatures seen in the forward fits particle data, which is about an order of magnitude higher than previously reported in particle data surveys (Bagenal & Delamere, 2011,https://doi.org/10.1029/2010JA016294). 

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4. Simulating Long‐Term Dynamics of Radiation Belt Electrons Using DREAM3D Model

   https://doi.org/10.1029/2023JA032286  

   Lee, Sang‐Yun; Tu, Weichao; Cunningham, Gregory S; Cowee, Misa M; Wang, Dedong; Shprits, Yuri Y; Henderson, Michael G; Reeves, Geoffrey D (February 2024, Journal of Geophysical Research: Space Physics)

   Abstract We compared the performance of DREAM3D simulations in reproducing the long‐term radiation belt dynamics observed by Van Allen Probes over the entire year of 2017 with various boundary conditions (BCs) and model inputs. Specifically, we investigated the effects of three different outer boundary conditions, two different low‐energy boundary conditions for seed electrons, four different radial diffusion (RD) coefficients (D_LL), four hiss wave models, and two chorus wave models from the literature. Using the outer boundary condition driven by GOES data, our benchmark simulation generally well reproduces the observed radiation belt dynamics insideL* = 6, with a better model performance at lowerμthan higherμ, whereμis the first adiabatic invariant. By varying the boundary conditions and inputs, we find that: (a) The data‐driven outer boundary condition is critical to the model performance, while adding in the data‐driven seed population doesn't further improve the performance. (b) The model shows comparable performance withD_LLfrom Brautigam and Albert (2000,https://doi.org/10.1029/1999ja900344), Ozeke et al. (2014,https://doi.org/10.1002/2013ja019204), and Liu et al. (2016,https://doi.org/10.1002/2015gl067398), while withD_LLfrom Ali et al. (2016,https://doi.org/10.1002/2016ja023002) the model shows less RD compared to data. (c) The model performance is similar with data‐based hiss models, but the results show faster loss is still needed inside the plasmasphere. (d) The model performs similarly with the two different chorus models, but better capturing the electron enhancement at higherμusing the Wang et al. (2019,https://doi.org/10.1029/2018ja026183) model due to its stronger wave power, since local heating for higher energy electrons is under‐reproduced in the current model. 

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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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