Simultaneous ground and satellite observations of discrete auroral arcs, substorm aurora, and Alfvénic aurora with FAST and THEMIS GBO

Abstract

AbstractThree distinct types of aurora are observed during separate events, using simultaneous measurements on the ground with all sky imagers from the THEMIS Ground‐Based Observatories and in situ with the FAST auroral satellite. The three cases show discrete stable arcs, substorm aurora, and Alfvénic aurora. The field‐aligned current structure associated with each type of aurora is shown to agree with contemporary auroral models. Inverted‐V type aurora with electron energy peaks of 1–10 keV are observed, and are associated with upward current regions and discrete auroral arcs seen in the all sky imagers. Downward currents are also identified and correlated with regions without visible aurora, and Alfvénic electron precipitation is associated with mixed current regions and dynamic aurora evident in the all sky images. The substorm aurora observed also shows upward current regions and inverted‐V's associated with bright spots in the ground‐based images. The images shown in association with the substorm aurora correlate well with existing substorm models, including that of Akasofu [1964]. In this study we present these new ground and satellite conjunctions and use them to confirm existing theories of auroral acceleration mechanisms. Additionally, we compare the observations to existing substorm models and investigate differences between specific substorms and the various auroral forms associated with them.