The iSTORM Instrument for Airborne Measurements of Gamma-Ray Emissions from Thunderstorms

Abstract

The in-Situ Thunderstorm Observer for Radiation Mechanisms (iSTORM) is a gamma-ray spectrometer to study gamma-ray transients originating from thunderstorms, such as glows and terrestrial gamma-ray flashes (TGFs). It is designed and built by the U.S. Naval Research Laboratory for deployment aboard a NASA ER-2 aircraft. Using an array of 32 one-inch-diameter ${\mathrm{CeBr}}_3$ scintillators read out with silicon photomultipliers (SiPMs), the instrument achieves an energy range of $\sim 250\mathrm{keV}$ to $5\mathrm{MeV}$ under flight conditions, with a total geometrical area of $157\mathrm{c}{\mathrm{m}}^2$. One of two gamma-ray instruments in the ALOFT campaign, iSTORM recorded glows, terrestrial gamma-ray flashes (TGFs), and the newly discovered flickering gamma-ray flashes (FGFs).