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

Abstract

[1] Three 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.Citation: Colpitts, C. A., S. Hakimi, C. A. Cattell, J. Dombeck, and M. Maas (2013), Simultaneous ground and satellite observations of discrete auroral arcs, substorm aurora, and Alfve´nic aurora with FAST and THEMIS GBO, J. Geophys.

Space Plasma Physics: A Review

“…Discrete auroras sometimes show highly structured shapes whose scale sizes are ∼1 km or less [498], [499], [500]. Such thin arcs often behave more dynamically (i.e., not quasistatic), some of which is closely related to time-varying magnetic field-aligned electric fields associated with dispersive Alfvén waves [501], [502], [503], [504]. Details of the smallscale dynamic discrete aurora can be found in the review of Kataoka et al [505].…”

Simultaneous Measurements of Substorm‐Related Electron Energization in the Ionosphere and the Plasma Sheet

“…The visible aurora is caused by precipitating electrons with~1-10 keV energy (Colpitts et al, 2013;Tanskanen et al, 1981). Precipitating electron population can contain a high-energy tail of electrons of primary energies ranging from 10 to 100 keV that cause X-ray emissions (Brown, 1966).…”

Scale size‐dependent characteristics of the nightside aurora

“…It is in general difficult to distinguish between the Inverted V/monoenergetic and Alfvénic/broadband precipitation by observing the discrete aurora alone. For example, Colpitts et al [2013] observed Alfvénic aurora intermittently and perhaps simultaneously with inverted V aurora during an event of continuous substorm activity. They described the aurora as extremely dynamic changing on timescales of seconds with bright spots and arcs that were not as elongated in the east-west direction as during typical inverted V events.…”