Differentiating diffuse auroras based on phenomenology

Abstract

Abstract. There is mounting evidence which suggests that pulsating auroral patches often move with convection. This study is an initial step at identifying the differences between patches that move with convection and those that do not. While many properties of pulsating patches vary, here we outline criteria for separating pulsating auroral patches into three categories based on two properties: their structural stability and the spatial extent of their pulsations. Patchy aurora is characterized by stable structures whose pulsations are limited to small regions. Patchy pulsating aurora consists of stable patches whose pulsations are far less subtle and occur throughout much of their area. Amorphous pulsating auroral structures are unstable – very rapidly evolving – and can pulsate over their entire area. The speed with which amorphous pulsating aurora evolves makes their motion difficult to ascertain and seems unrelated to the E×B drifting of cold, equatorial plasma.

Responses of Different Types of Pulsating Aurora in Cosmic Noise Absorption

“…The motion velocity (~2 km/s) is much faster than the convection motion of PPA patches (Yang et al, 2017). This patch entirely disappeared after 08:10:21 UT, with a total lifespan of 42 s. The fast motion, rapidly varying shape, and short lifetime are all characteristics of APA (Grono & Donovan, 2018).…”

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A recent study (Grono & Donovan, 2018, https://doi.org/10.5194/angeo-36-891-2018 reported two distinct categories of pulsating aurora: patchy pulsating aurora (PPA) and amorphous pulsating aurora (APA). In this study we compare the auroral intensity of five PPA events and seven APA events monitored by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) All-Sky Imagers with co-located cosmic noise absorption (CNA) from the Geospace Observatory wide-beam riometers.

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Constraining the Source Regions of Pulsating Auroras

“…Pulsating aurora events are often identified using keograms (e.g., Grono & Donovan, 2018;Jones et al, 2013;Partamies et al, 2017;Yang et al, 2017) due to the distinctive striations produced by pulsating aurora in these images. The characteristic structuring of PPA and PA creates pathlines tracing the trajectories of the corresponding patches.…”

Surveying pulsating auroras

“…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).…”

“…Historically, pulsating auroras were subcategorized by Royrvik and Davis (1977) into patches, arcs, and arc segments, but modern literature generally only refers to "pulsating aurora" and "pulsating auroral patches" (e.g., Yang et al, 2019;Partamies et al, 2019;Ozaki et al, 2019) and would not consider the "streaming arc" of Royrvik and Davis (1977) to be a type of pulsating aurora. Grono and Donovan (2018) recently used all-sky camera data to define criteria for differentiating pulsating aurora based on their phenomenology. They identified three types of pulsating aurora which were separable based on their pulsation and structure.…”