Investigating terrestrial gamma-ray flashes with Fermi GBM and LIS

Abstract:

We search for simultaneous detections of Terrestrial Gamma-ray Flashes (TGFs) with the Gamma-ray Burst Monitor (GBM) and the Lightning Imaging Sensor (LIS) in order to investigate the temporal and spatial relationships between TGFs and lightning. Only TGFs detected with the VLF radio networks WWLLN and ENTLN are used, thereby reducing the TGF location error from over 300 km to ~10 km. This results in a sample of 877 TGFs. We begin by identifying incidences of temporal and spatial FOV coincidence between LIS and the TGF sample and then investigate those at the LIS Group and Flash levels. Two incidences of FOV coincidence are found, TGF120124320a and TGF120524874, each of which has one or more LIS flashes. However, the flashes are either too far away in position or time to be convincing associations considering the TGF location uncertainties and our understanding of the TGF-lightning relationship. The LIS optical signals are therefore likely chance coincidences. We continue to expand the GBM sample, obtaining radio-located TGFs at a rate of ~300 per year, so that a joint GBM-LIS detection may be found soon.