Réunion de lancement du projet LICORNE

A natural lightning flash is a powerful phenomenon, still not totally understood. Lightning mapping techniques, like difference of time-of-arrival technique in the VHF domain, provide key characterization of the development of both Intra-Cloud (IC) and Cloud-to-ground (CG) lightning flashes. Combined to cloud remote sensing observations, the lightning flash can be replaced in its environmental context. However questions remain on the physical processes that trigger a lightning flash, as the ambient macroscopic electric field inside the cloud is typically one order of magnitude less than that required for dielectric breakdown. One hypothesis currently considered by the community is that a lightning flash can be triggered by an avalanche of runaway electrons created by cosmic ray-induced extensive air showers with energy in excess of 1016 eV (Gurevich et al, 1992). On the other hand, it has been evidenced that terrestrial gamma-ray flashes may be produced in association with natural lightning flashes (e.g. Cummer et al., 2005; Splitt et al., 2010). Consequently further investigations are required to not only document but also to understand the complex physical processes involved here through a multi-disciplinary study that will require both observations and modeling exercises. The LIghtning and COsmic Rays in Natural Environment project (LICORNE) aims at gathering French Scientists working in High-energy Particle and Atmospheric Sciences on a common project dedicated to the study of the impact of natural cosmic rays on the occurrence of natural lightning flashes and on the characterization of high-energy particles radiated during natural lightning flashes. In its first year, the LICORNE project will: i) perform a rather exhaustive literature review on the interaction between cosmic rays and lightning flashes, ii) identify strengths and weaknesses of the Consortium in its current composition, iii) explore available lightning and air shower observations above the CODALEMA site during the recent years to help define a realistic Science Plan that will drive the development phase of the project, including an observational strategy combining relevant instrumentation, and a modeling strategy in preparation for the interpretation of the observations. A preliminary approach could be based on long-term collection of detailed records of air showers and lightning flashes for storms passing above a single state-of-the-art instrumental site - already existing or to build - and on the analysis of temporal and spatial correlations in the observations to provide key inputs for modeling investigations coupling high-energy particle physics and lightning phenomenology. The LICORNE project includes physicists of the Terrestrial Gamma-ray Flashes (TGFs) French community for shared analysis using lightning and cosmic rays data but no gamma imager is foreseen in this project.