Thunderstorm Electric Field Modeling from Electrification to Terrestrial Gamma-ray Flash Production

Knowledge of the electric field structures inside thunderstorms is necessary for understanding of thunderstorm electrification, lightning initiation, and terrestrial gamma-ray flash (TGF) production. However, existing knowledge comes largely from weather balloon measurements that provide a limited view that entangles motion of the balloon (spatial variability) with overall evolution of the storm (temporal variability). More advanced interpretation of such data and connection of it to the broader context requires comprehensive modeling of the full process. We describe such a model, built on simple approximations of electrification processes, the resulting currents, charge structures, and electric fields, including a crude probabilistic lightning model. The result is a reasonably realistic model of thunderstorm field and its evolution that can be used to predict possible balloon measurements of electric field, with results that are in good qualitative agreement with existing balloon data. The resulting electric field is then also used as input to a Geant4 simulation of relativistic electron behavior to understand when and where TGF production is likely to occur in the dynamic thunderstorm electric field. The combination of meteorological drivers of electrification, constrained by comparison to balloon data, and in turn how they may give rise to TGFs, provides a unique tool to aid in our understanding of such processes and how they are linked.