Journal Article

First Daytime Red‐Line Emission Measurements of the Stable Auroral Red (SAR) Arcs

Pallamraju, Duggirala, Upadhyay, Kshitiz

2024

Overview

We present the first ground‐based measurements of daytime stable auroral red (SAR) arc using OI 630.0 nm emissions. SAR arc is a direct consequence of heat conduction from the inner‐magnetosphere to the ionospheric regions characterized by increased electron temperatures and low electron density in the region of mid‐latitude trough. So far, SAR arc emissions have only been reported for nighttime conditions. For the present study, daytime optical measurements were enabled using a high‐resolution imaging echelle spectrograph from Boston (42.36°N, 71.05°W, MLAT ≈ 53°). Simultaneous Millstone Hill Incoherent Scatter Radar and Defense Meteorological Satellite Program measurements of electron density and temperature confirm our findings. Forward modeling approach enabled estimation of daytime electron temperatures in 200–650 km altitude during this SAR arc event to be varying between 3,500 and 4,400 K. These observations open numerous possibilities of optical investigations of magnetospheric‐ionospheric interactions during daytime, when the upper atmosphere is dynamic with large gradients in ionospheric conductivities, temperatures, and winds. Plain Language Summary A latitudinally narrow and zonally elongated channel consisting of enhanced red‐line emissions are known to be present, on occasions, in the optical measurements in the sub‐auroral latitudes and are referred to as the stable auroral red (SAR) arcs. These are now known to be caused by the conduction of heat from the Ring current region into the ionosphere. Earlier studies suggested an increased electron temperature (above ∼300 km altitude) collocated with the low electron density region of ionospheric trough. So far, observations of SAR arcs have only been reported for the night time. In the daytime, due to the presence of sunlight the atmospheric conditions are different, so also are the upper atmospheric dynamics. The measurements of SAR arcs in the daytime are also challenging as the background solar brightness is very large. In this work, by making use of high spectral resolution optical measurements in the daytime, we present the first measurements of daytime SAR arcs and perform model calculations to estimate the values of electron temperature in the 200–650 km altitude range to be varying in the range of 3,500–4400 K. Key Points Ground‐based measurements of O(1D) dayglow showed enhancement in emissions on a geomagnetically disturbed day at a mid‐latitude location Complementary data sets revealed the increase in optical emissions to be stable auroral red (SAR) arcs, which are associated with elevated electron temperatures This study presents the first ground‐based detection of daytime SAR arcs in OI 630.0 nm red‐line emissions

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Altitude / Atmospheric conditions / Atmospheric dynamics / Conduction / Conduction heating / Conductive heat transfer / Daytime / Density / DMSP satellites / echelle spectroscopy / Electron density / Electron energy / electron temperature / Electron temperatures / Electrons / Emission measurements / Emissions / Heat conduction / Incoherent scatter radar / Ionosphere / Ionospheric trough / Latitude / Magnetospheres / Meteorological satellite program / Meteorological satellites / mid‐latitude upper atmosphere / Night / OI 630.0 nm dayglow / Optical measurement / Ring currents / SAR (radar) / SAR arcs / space weather phenomena / Spectral resolution / Sunlight / Temperature / Upper atmosphere / Winds