IMAGE FUV and in situ FAST particle observations of substorm aurorae

Abstract

[1] Images from the IMAGE Wide-band Imaging Camera (WIC) and Spectrographic Imager (SI) channels SI-12 and SI-13 were compared to in situ data taken by FAST during several substorms. FAST spacecraft observations have shown that the high latitude auroral ionosphere has several distinct regions. Intense auroras are seen in regions of upward directed quasi static electric fields and of Alfven wave accelerated superthermal electrons. In two of the cases presented, the satellite passed through an active poleward propagating substorm surge on its duskward flank. Both show that the superthermal wave accelerated component to be on the polar cap boundary of the surge, and that it could be distinguished from quasi static field ''inverted V'' precipitation which occurred at the more equatorward parts of the auroral oval. In one of these cases, the surge was accompanied by intense ion outflow. Three cases showed the FAST satellite passing through the substorm aurora at midnight or the dawn side outside of the surge and the wave accelerated electrons were less clearly separated from the inverted V type precipitation. The wave accelerated electrons were seen to be part of very shortlived transient events, i.e., bursts. The region of auroral forms, associated with Alfven waves exhibit relatively soft auroral precipitation with very intense electron fluxes. By comparing the intensity of the WIC and SI-13 channels of IMAGE FUV, it is possible sometimes to distinguish optically between the two types of regions. Global imaging of the two regions would allow the separation of quasi-static plasma convection regions containing inverted V-s from regions of Alfven wave driven electrons signifying substorm related magnetic field dynamics.

Alfvén Waves and Their Roles in the Dynamics of the Earth’s Magnetotail: A Review

“…The study demonstrated that the leading edge of the auroral surge was energized by Alfvén waves rather than by quasi-static field-aligned currents and related electron inverted Vs (Mende et al 2003a). During later phases of substorm development, the Alfvén wave-accelerated electrons and the corresponding auroral surge were seen closer to the polar cap boundary (also Mende et al 2002Mende et al , 2003b.…”

PFISR observations of strong azimuthal flow bursts in the ionosphere and their relation to nightside aurora

“…As evident in the top panel, the satellite detected the poleward boundary of the auroral oval (OCB) at 08:32:20 UT, characterized by soft electron precipitation and located at À75.51 magnetic latitude at 2350 MLT. At lower latitudes, two significant inverted-V arcs, pointed by arrows, were seen adjacent to each other and were bounded by narrow broader band auroral precipitation regions that have been associated with Alfvé nic electron energization (Mende et al, 2003 and reference therein). It seems that the first inverted-V arc was associated with the ''north-south'' structure and the second one with the east-west structure.…”

ULF Waves above the Nightside Auroral Oval during Substorm Onset

“…Wygant et al, 2000], accelerating electrons to provide the aurora [Watt and Rankin, 2009, 2010, 2012. Additionally, we will explore the different types of magnetotail instabilities that may occur at the inner edge of the plasma sheet, since there is evidence that substorm onset aurora is associated with acceleration by shear Alfvén waves [Mende et al, 2003].…”