XStorm: a Lightweight Gamma-ray Spectrometer Designed to Detect Terrestrial Gamma ray Flashes and Glows

Thunderstorms produce high-energy radiation events such as Terrestrial gamma ray flashes (TGFs) and Gamma ray Glows (GRGs) via bremsstrahlung during the acceleration of runaway electrons to relativistic energies. Although TGFs and GRGs are believed to originate from the same physical process (relativistic runaway electron avalanche (RREA)), TGFs are intense sub-millisecond bursts of X-rays, while GRGs are less intense, long-lasting X-rays emissions. 

Several balloon flight campaigns are being prepared to observe and better understand these energetic phenomena such as Strateole-2 and OREO funded by the French Space Agency (CNES). Strateole-2 is a stratospheric balloon campaign using superpressure balloons flying for several months between 18 and 20 km in the intertropical region (planned for the end of 2026). OREO is a lightweight balloon project aiming to launch several radiosondes directly into thunderstorms to probe in-situ high-energy emissions associated with the electrical activity.

In order to participate in these projects a dedicated instrument named XStorm has been developed [Pallu, et al., JGR, 128, e2023JD039180, 2023, https://doi.org/10.1029/2023JD039180] with a view to perform in-situ and remote measurements. XStorm is a lightweight gamma-ray spectrometer its conception allow us to detect gamma ray glows and TGFs near the sources.

In addition, XStorm contributes to a new ground-based measurement campaign that involves installing it at key positions to detect and analyze TGFs as well as GRGs. 

In this contribution, we present the XStorm detector, detailing its electronic architecture, operational principles, and performances, as well as the campaigns in which it will be used.