Cosmic Ray Indirect Rapporteur Report (37th ICRC)

This report summarizes the physics results presented as part of the cosmic-ray indirect (CRI) session of the 37thICRC conference. Updated measurements on cosmic-ray energy spectrum, mass composition, and arrival direction distributions were presented by several collaborations, spanning the energy range of a few TeV up to the highest observed energies. We select some of the results which were highlighted by the respective discussion leaders or which presented new results at this conference. Results on atmospheric phenomena, including TGFs and thunderstorms are also presented. We see a few interesting trends in the presented data. Among these are, the increased use of IACT's to study cosmic-rays among experiments primarily intended for gamma-ray measurements. Another, is the continued development of radio detection of air showers. Multi-component detectors are becoming the preferred detection mode, as the knowledge of how to integrate the different information about an air shower collected by the different detector components improves. The main physics questions about the origins of cosmic rays, both galactic and extra-galactic, remain open. Increased statistics and improved analyses allow for refining and better constraining theoretical models, but no definitive answers can be claimed thus far. Looking forward, the field is moving at a rapid pace; Several detectors upgrades are underway, data is continually coming in and analyzed, old data being made public for a wider audience and a new generation of scientists to examine, with new tools and approaches that will hopefully result in new insights to help solve the open questions on cosmic-rays.