Substorm triggering by poleward boundary intensification and related equatorward propagation

Recently, a revised auroral substorm onset sequence has been proposed, in which onset is preceded by a poleward boundary intensification (PBI) and subsequent equatorward propagation of N-S-aligned auroral features to breakup arc latitudes. We reanalyzed 20 randomly selected samples of the Nishimura et al. (2010) 251-event database and show in greater detail to what degree the observed features in this subset of events are consistent with the proposed scenario. To assess the sensitivity of space-based imagers for seeing this scenario, we calibrated the absolute responsivity of the THEMIS ground-based imagers. We also show that although not suitable for studies from apogee, IMAGE/FUV imagers can also observe a consistent scenario from a lower altitude. We conclude that in some cases PBIs and subsequent plasma flows can be effective in providing a trigger if the inner magnetosphere is ready to produce a substorm.