First optical observations of interhemispheric electron reflections within pulsating aurora

Abstract

A case study of a pulsating auroral event imaged optically at high time resolution presents direct observational evidence in agreement with the interhemispheric electron bouncing predicted by the SuperThermal Electron Transport model. “Pulsation‐on” times are identified and subsequent equally spaced fainter pulsations are also noted and can be explained by a portion/percentage of the primary precipitating electrons reflecting upward from the ionosphere, traveling to the opposite hemisphere and reflecting upward again. The high time resolution of these data, combined with the short duration of the pulsation‐on time (∼1 s) and the relatively long spacing between pulsations (∼6 to 9 s) made it possible to observe the faint optical pulses caused by the reflected electrons coming from the opposite hemisphere.

Major pathways to electron distribution function formation in regions of diffuse aurora

“…The idea of the role of MI coupling processes in the formation of diffuse aurora that has been introduced in our previous research by Khazanov et al . [, , ] was recently conformed by first optical observations of interhemispheric electron reflections within pulsating aurora by Samara et al []. In this paper they presented ground‐based optical signatures of the aurora showing evidence that a certain type of aurora is caused by electrons bouncing back and forth between the two hemispheres.…”

Diffuse and Pulsating Aurora

“…e-POP satellite observations over pulsating aurora have also detected upgoing low-energy electrons, which are considered to be backscattered secondary electrons (Knudsen et al, 2015). Samara et al (2017) highlighted a case where the temporal and intensity variations of pulsating auroral are in good agreement with the predictions of the SuperThermal Electron Transport (STET) code. A pulsating aurora event was observed at Poker Flat, AK with the MOOSE imager suite in multiple fields of view but it was the very narrow field of view imager (4 degree field of view) that was operated at 56 frames per second (16 ms exposure time) with no filter that enabled the observations of the secondary electron peaks.…”

“…It can be said that a significant part of new insights come from such a change coupled with our ability to handle much larger volumes of data, a necessity when recording many hours a night of auroral activity. The recently observed optical signatures of inter-hemispheric electron reflections within pulsating aurora (Samara et al, 2017) are in that category. These had been inferred to be observable from prior theory and modeling work but even initial verification from optical signatures had been elusive partly because of the observational conditions needed.…”

How Magnetically Conjugate Atmospheres and the Magnetosphere Participate in the Formation of Low‐Energy Electron Precipitation in the Region of Diffuse Aurora

“…The source of the lower‐energy electrons was further developed quantitatively by Khazanov et al (2016) who introduced the idea of multiple atmospheric reflection (or backscatter) between the conjugate atmospheres being critical to the formation of these electrons. This was later verified experimentally by Samara et al (2017) in their case study of a pulsating auroral event imaged optically at high time resolution.…”

“…The structure of this code, however, as well as the approach for the numerical implementation of kinetic electron equation in an inhomogeneous magnetic field, was based on the photoelectron transport code presented by Khazanov (1979). This code was further generalized for MI coupling studies in the region of diffuse aurora by Khazanov et al (2014, 2016, 2017) and validated experimentally by Samara et al (2017) in their case study of a pulsating auroral event imaged optically at high time resolution. The results of our simulation were also successfully compared to FAST (Khazanov et al, 2016) and DMSP (Wing et al, 2019) observations.…”