A. Lindanger, C. A. Skeie, M. Marisaldi, I. Bjørge-Engeland, N. Østgaard, A. Mezentsev, V. Reglero, T. Neubert, Statistical Evidence of Terrestrial Gamma-ray Flashes Production During the Early Stages of Lightning Flashes, AGU Fall Meeting, New Orleans, US, Dec. 13-17, 2021