New Insight Into the Transition From a SAR Arc to STEVE

• Published in: Geophysical research letters 2023-03, Vol.50 (6), p.n/a
• Main Authors: Gillies, D. M., Liang, J., Gallardo‐Lacourt, B., Donovan, E.
• Format: Article
• Language: English
• Subjects: Airglow; Auroras; Broadband; Colour; Emission analysis; Emissions; Flow channels; Ionospheric models; Lakes; Luminosity; Mathematical models; Night sky; Parameters; SAR arc; Scientists; Southern Hemisphere; STEVE; sub auroral; Thermal emission; Velocity; Wavelengths
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL101205

In this study, we present an analysis of the spectral transition of a Stable Auroral Red (SAR) arc to Strong Thermal Emission Velocity Enhancement (STEVE) emission observed by the Transition Region Explorer (TREx) Spectrograph on the night of 10 April 2022, recorded overhead in Lucky Lake, Saskatchewan. On this night, we see an unusually bright (∼2 kR) SAR arc with enhanced ionospheric flow channels in the conjugate southern hemisphere. Over a short time, on the order of minutes, we observe the spectra change from the typical SAR arc pure redline (630 and 636 nm) emission to the air glow continuum, a broadband enhancement across all wavelengths, characteristic of STEVE. We propose the presence of threshold conditions required for the SAR arc to evolve into STEVE. In addition, we present parameters such as transition times, luminosities, and arc motion to be applied to ionospheric models. Plain Language Summary The current fascination with a night sky phenomenon known as Strong Thermal Emission Velocity Enhancement (STEVE) has captured the attention of scientists and citizen scientists in recent years. STEVE is an unusual ribbon of bright mauve light that extends across the night sky far to the south from where we typically see the aurora. STEVE’s location in the night sky and its unusual coloring have baffled scientists’ and prompted some key questions in the attempt to understand it. In this study, we look at a recent development in the origin of STEVE, the connection to a well‐known airglow phenomenon: Stable Red Auroral, or Stable Auroral Red (SAR), arcs. SAR arcs are dim wide bands of pure deep red color. Recently, a connection has been identified between SAR arcs and STEVE. This study looks at the spectrum, or emission fingerprint, of a particularly unusual SAR arc and its evolution into STEVE. We identify specific threshold conditions surrounding the transition of the SAR arc into STEVE. We also present parameters, such as transition time, as well as luminosity and motion variations during the transition. Our results can be applied to models in the hope of advancing our understanding of how this process occurs. Key Points Detailed analysis of spectral transition of a Stable Auroral Red (SAR) Arc into Strong Thermal Emission Velocity Enhancement (STEVE) emission Ionospheric threshold conditions may be a requirement for the evolution of STEVE Basic parameters of transition features from SAR Arc to STEVE presented