Streamer-like red line diffuse auroras driven by time domain structures and ECH waves associated with a plasma injection and braking ion flows

TL;DR

This study reveals that plasma sheet electron pitch-angle scattering by time-domain structures and ECH waves drives streamer-like red-line auroras, linking low-energy electron precipitation with magnetospheric injections and ion flows.

Contribution

It is the first to connect red-line auroras with specific plasma wave interactions and electron scattering processes using combined spacecraft and ground-based observations.

Findings

Red-line auroras are associated with magnetospheric electron injections.

Strong correlation (~0.9) between red-line intensities and precipitating fluxes.

Consistent modeling and optical inference support the scattering mechanism.

Abstract

Auroral streamers are important meso-scale processes of dynamic magnetosphere-ionosphere coupling, typically studied using imagers sensitive to energetic (>1 keV) electron precipitation, such as all-sky imagers (ASIs). This paper reports streamer-like red-line auroras, representing low-energy (<1 keV) precipitation, observed poleward of a black aurora and an auroral torch. These red-line auroras were associated with a magnetospheric electron injection and braking ion flows. Observations were made using the THEMIS spacecraft and ground-based imagers, including the ASI, REGO, and meridian scanning photometer (MSP) at Fort Smith. We identify plasma sheet electron pitch-angle scattering by time-domain structures (TDSs) and electron cyclotron harmonics (ECH) waves as the driver of these red-line auroras, because of (1) a strong correlation (~0.9) between observed red-line intensities and precipitating fluxes; (2) consistent red-line intensities from auroral transport code forward modeling, and (3) consistent precipitation characteristic energies from MSP optical inference and quasi-linear estimates.