@InProceedings{BelzAKKLPRRSSS:2022:NeObIn,
               author = "Belz, John and Abbasi, Rasha and Kieu, Ny and Krehbiel, Paul R. 
                         and LeVon, Ryan and Petrizze, Alex and Remington, Jackson and 
                         Rison, William and Saba, Marcelo Magalh{\~a}es Fares and Smout, 
                         Kieran and Stanley, Mark A.",
          affiliation = "{University of Utah} and {University of Utah} and {Loyola 
                         University Chicago} and {New Mexico Tech} and {University of Utah} 
                         and {University of Utah} and {University of Utah} and {New Mexico 
                         Tech} and {Instituto Nacional de Pesquisas Espaciais (INPE)} and 
                         {University of Utah} and {New Mexico Institute of Mining and 
                         Technology}",
                title = "New Observations of Intermediate-Duration Downward Terrestrial 
                         Gamma-ray Flashes",
                 year = "2022",
         organization = "AGU Fall Meeting",
            publisher = "AGU",
             abstract = "We present the most recent observations of the lightning research 
                         program at the Telescope Array cosmic ray observatory in Utah, 
                         U.S.A. This program focuses on understanding the initial breakdown 
                         stage of lightning through observations of downward Terrestrial 
                         Gamma-ray Flashes (TGFs). The Telescope Array Surface Detector 
                         (TASD) is a 700 square kilometer array of plastic scintillator 
                         detectors located in Utah's western desert. It consists of 507 
                         three-square-meter detectors on a 1.2 km grid. The TASD was 
                         designed to detect particle showers generated by the interaction 
                         of ultra-high energy cosmic rays with the Earth's atmosphere. 
                         Recent observations have demonstrated that Terrestrial Gamma-ray 
                         Flashes (TGFs) detected by satellites are associated with 
                         high-current energetic in-cloud pulses during ascending negative 
                         leaders. Meanwhile, a relatively small number of observations have 
                         been made of TGFs on the ground, owing to the greater atmospheric 
                         attenuation of gamma rays and the relatively rare occurrence of 
                         TGFs sufficiently close to detectors. Previously (Abbasi et al 
                         2018, Belz et al 2020) we reported joint observations by TASD, 
                         Lightning Mapping Array (LMA), sferic sensor and broadband 
                         interferometer of particle showers coincident with lightning. 
                         These consisted of energetic showers of approximately 5 
                         microsecond duration with footprints on the ground of order 10 
                         square kilometers, originating in the first one to two 
                         milliseconds of downward lightning leaders and coincident with 
                         high-current processes within the leaders. Scintillator waveform 
                         and simulation studies confirmed that these showers must consist 
                         primarily of gamma radiation, thus the observations were 
                         identified TGFs near their initiation threshold. The TASD-observed 
                         downward TGFs were in general of shorter duration and lower 
                         fluence than their satellite-detected upward counterparts. Here, 
                         we report the new observation and study via the Monte Carlo 
                         technique of several events of significantly longer duration and 
                         higher fluence than previously observed. These events bridge the 
                         gap between the prior TASD and satellite based detections, and 
                         thus further demonstrate the similarity between the upward and 
                         downward varieties of TGF.",
  conference-location = "Chicago, IL",
      conference-year = "12-16 Dec. 2022",
        urlaccessdate = "06 jun. 2024"
}