Direct Evidence for Throat Aurora Being the Ionospheric Signature of Magnetopause Transient and Reflecting Localized Magnetopause Indentations

Abstract

Magnetopause transients, observing as brief entries into the magnetosheath by satellites, are commonly observed in the vicinity of the magnetopause and have been explained by several possible mechanisms. However, satellite observations alone are insufficient to determine the dynamics and context of transients. Throat auroras are characterized as north‐south aligned discrete auroral forms extending from the equatorward edge of the discrete auroral oval that are only observed near dayside convection throat region and have been suggested as the ionospheric signature of localized magnetopause indentations. Using coordinated observations from the Magnetospheric Multiscale Mission (MMS) and ground‐based all‐sky imagers, we show apparent one‐to‐one correspondences between transients observed by MMS near the subsolar magnetopause and throat auroras observed on the ground. The correspondence is valid not only for typical throat aurora with larger spatial scale but also for these with tiny scales. We even notice that the transient durations observed by satellite are approximately proportional to the width (east‐west extension) of the throat aurora. These results provide direct evidence that throat auroras are ground signatures for the magnetopause transients. With the aid of auroral observations, we suggest that these transients reflect localized magnetopause indentations but are not produced by motion of the entire magnetopause. We also found that most transients observed here are associated with earthward flow enhancements, which indicates that high‐speed jets in the magnetosheath could be a driver for producing these transients.

Energetic electron enhancements under the radiation belt (<i>L</i> < 1.2) during a non-storm interval on 1 August 2008

“…In addition, similar effects of the foreshock pressure pulses and magnetosheath jets in the magnetosphere were reported (e.g. Korotova et al, 2011;Hietala et al, 2012).…”

Observational Evidence for Throat Aurora Being Associated With Magnetopause Reconnection

“…These deformations are supposed to be dented structures on the subsolar magnetopause. Later, Han et al () found one‐to‐one correspondences between throat auroras observed on the ground and magnetopause transients observed near the subsolar magnetopause, which have been suggested to be the direct evidence for throat auroras being the ionospheric signature of magnetopause indentations. In addition, it was found that the spatial scale of the magnetopause indentation can be as large as ~2.0 × 3.0 R E (Earth radius) after mapping a throat aurora to the geomagnetic equatorial plane, and the occurrence rates are as high as ~50% and ~25% counted by day and by 10 min, respectively (Han et al, ).…”

Energetic electron enhancements under radiation belt (L

“…whereas southward IMF has a weaker influence on its occurrence. Based on the comprehensive 613 study of properties of throat aurora, Han et al (2018) concluded that throat auroras are definite 614 ground signatures for local magnetopause deformations and compressions produced by 615 magnetosheath plasma jet impact. They also provided direct evidence that the source of 616…”