Progress and challenges in understanding the ambient solar magnetic field, heating, and spectral irradiance

The Committee on Space Research (COSPAR) International Space Weather Action Teams (ISWAT) has the objective of addressing key problems in space weather research and forecasting. To accomplish this objective, several teams comprised of experts from a variety of fields and specialties have formed to specifically focus on challenging space weather problems, linking physical domains of the Sun-Earth system and addressing roadblocks slowing progress in space weather research and forecasting. The S2 Cluster is focused primarily on the solar magnetic field, heating of the corona, and solar spectral irradiance. The goal of this paper is to describe the central objectives of the six S2 Action Teams, summarize the current state of knowledge of the topic that each team is focusing on, identify key science gaps that need to be addressed in each area, supply key recommendations for the community to focus on to facilitate progress, provide a likely picture of progress in the next five years and plausible timelines of achievement beyond that, and finally link the S2 Cluster efforts to other ISWAT research domains.