Patch Size Evolution During Pulsating Aurora

TL;DR

This study analyzes the evolution of patch sizes during pulsating aurora events, revealing different trends and their associations with auroral and substorm dynamics, using automated detection over 150 events.

Contribution

It introduces an automated routine for detecting auroral patches and systematically characterizes patch size trends during pulsating auroras, linking these trends to substorm phases and energetic electron behavior.

Findings

Increasing patch sizes correlate with shorter lifetimes.

Events with increasing patch sizes occur mainly during substorm expansion phases.

Patch size trends relate to auroral energy deposition patterns.

Abstract

We report both decreasing and increasing trends in the patch sizes during pulsating aurora events. About 150 pulsating auroral events over the Fennoscandian Lapland have been successfully analyzed for their average patch size, total patch area, and number of patches as a function of event time, typically 1-2 hr. An automatic routine has been developed to detect patches in the all-sky camera images. In addition to events with decreasing and increasing average patch size evolution over the course of the pulsating aurora, events with no size trends and events with intermittently increasing and decreasing patch size trends were also found. In this study, we have analyzed a subset of events for which the average and total patch size systematically increase or decrease. The events with increasing patch size trend do not experience a decrease in the peak emission height, which was previously associated with the behavior of pulsating aurora precipitation. Furthermore, the events with increasing patch sizes have shorter lifetimes and twice as many substorm-injected energetic electrons at geosynchronous orbit as the events with decreasing patch sizes. Half of the events with increasing patch sizes occur during substorm expansion phases, while a majority (64%) of the ones with decreasing patch sizes take place during the recovery phase. These findings suggest that the visual appearance of pulsating aurora may be used as an indication of the pulsating aurora energy deposition to the atmosphere.