Constraining the Source Regions of Pulsating Auroras

Abstract

Pulsating auroras have often been erroneously discussed as if they are a single phenomenon. For this reason, the relationship between different pulsating auroras is poorly understood. Grono and Donovan (2018, https://doi.org/10.5194/angeo-36-891-2018) subcategorized pulsating auroras into amorphous pulsating, patchy pulsating, and patchy auroras, which are separable based on their pulsation and structuring. By comparing the latitudes of these auroras to the location of the proton aurora, we have constrained their source regions for the first time. Pulsating aurora does not occur poleward of the proton aurora. Amorphous pulsating aurora occurs within and equatorward of the proton aurora, while patchy pulsating and patchy auroras predominantly occur equatorward of the optical b2i boundary. This indicates that the characteristic structuring of the patchy auroras is unable to form outside of the mostly dipolar inner magnetosphere, but the wave‐particle interactions that produce auroral pulsations are less constrained, extending into the transition region where the magnetic field begins to stretch.

Surveying pulsating auroras

“…The ASIs capture panchromatic, or "white light", images of the aurora at a 3 s cadence on a 256 × 256 pixel charge-coupled device (CCD) and have been operating for over 10 years, amassing tens of millions of images. It can be surmised from Jones et al (2011) that pulsating auroras are visible within about 10 % of these images (Grono et al, 2017). Of the 21 imagers deployed across North America, those stationed at Rankin Inlet, Nunavut (RANK); Gillam, Manitoba (GILL); and Pinawa, Manitoba (PINA) were utilized for this study.…”

“…To identify the boundaries of each type, certain characteristic features are searched for. PPAs and PAs move with ionospheric convection (Yang et al, 2015(Yang et al, , 2017Grono et al, 2017;Grono and Donovan, 2018) and have a stable, welldefined structure that creates pathlines in keograms. Pathlines trace the trajectory of PPA and PA patches along the keogram meridian and arise due to the long-lived nature of PPA and PA patches.…”

“…Measurements of pulsating aurora event durations are conservative because ground-based cameras, our primary tool for optically observing the aurora, cannot operate past sunrise (Partamies et al, 2017). The lifetimes of individual 2 E. Grono and E. Donovan: Surveying pulsating aurora structures are known to range from a few seconds to tens of minutes (e.g., Grono et al, 2017;Grono and Donovan, 2018).…”

Inferring the source regions of pulsating auroras

“…However, PPA and PA exhibit the same structuring (Grono and Donovan, 2018) and have similar distributions both in the ionosphere (Grono and Donovan, 2019b) as well as relative to the proton aurora (Grono and Donovan, 2019a). This suggests that the same structuring processes may be responsible for both, and that if you were to infer the source region of PA from a distribution of longer-lived chorus packets, you would also be identifying the source region of PPA.…”

“…Furthermore, it is not uncommon to see pulsating aurora events featuring PPA and PA where these auroras persist until camera shutdown. Despite all of this, if APA is frequently caused by these same longer-lived chorus packets, then their distribution would be useless for identifying the PA and PPA source region since APA can occur in a broader region than PPA and PA (Grono and Donovan, 2019a).…”