Airborne and Ground-Level Searches for Ionizing Radiation from Thunderstorms with iSTORM

The in-Situ Thunderstorm Observer for Radiation Mechanisms (iSTORM) flew onboard the NASA ER-2 aircraft in Spring 2017 as part of the GOES-R Validation Flight Campaign. It consists of four scintillators to measure gamma rays, charged particles, and neutrons with compact, rugged readout and data storage. The readout measures both scintillation pulse amplitude and pulse shape to provide effective identification of neutrons and discrimination of pulse pile-up. The latter can distort the measurement of event energy, for example during bright Terrestrial Gamma-ray Flashes. We deployed similar systems at ground level in Huntsville, Alabama, to coordinate with ER-2 overflights and at the Smithsonian Tropical Research Institute in Panama as part of a thunderstorm broadband monitoring campaign. Here we report on measurements made by all three systems, including gamma-ray glows observed during storm overflights.