Geomagnetic substorms, responsible for creating brightly lit aurorae that can disrupt satellite communications and electric power grids, comprise a wealth of dynamic plasma processes. These processes and their interplay were discussed by about 130 scientists at a conference at Austria's Seggau Castle, organized by the Space Research Institute of the Austrian Academy of Sciences.
Recent advances in observational and computational capabilities have allowed closer comparison between observation and theory on current sheet instabilities associated with reconnection, ballooning modes, and different wave properties. For example, presentations at the meeting showed how theory combined with observations from ESA's Cluster satellite helped scientists conclude that the formation of an embedded current sheet occurred before the growth of the instability rather than from thinning the entire plasma sheet. Additionally, the evolution of instabilities leading to magnetic reconnection was reported by several theoretical studies at the meeting, which were complemented by presentations of in situ observations seen from Cluster and NASA's Time History of Events and Macroscale Interactions During Substorms (THEMIS) mission that detailed the characteristics of the reconnecting current sheet. Observations at the inner magnetosphere where the magnetic field configuration changes from tail-like to dipolar fields showed that instabilities such as ballooning modes are needed to explain the initial auroral arc formation near the equatorward edge of plasma sheet electron precipitation.