Properties of Auroral Beads Observed During Non-Substorm Times
Authors/Creators
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1.
University of Alaska Fairbanks
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2.
The Aerospace Corporation
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1.
University of Alaska Fairbanks
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2.
The Aerospace Corporation
Description
Abstract:
The formation of auroral beads often occurs before auroral substorms and is closely related to substorm onset instabilities. Auroral beads are uniquely discussed in terms of their relationship with substorm onset, and almost all substorms are preceded by auroral beads. Substorms are easily identifiable in auroral data and by using pre-existing catalogs or automatic routines. Conversely, auroral beads are relatively difficult to identify automatically, and if they appear at other times are often overlooked. Using the Time History of Events and Macroscale Interactions During Substorms All Sky Imagers (THEMIS ASI), we identified and categorized over 300 auroral bead events from 2007 to 2016. We observed auroral beads leading to substorms around 90% of the time, but 10% of the auroral beads formed preceding non-substorm events (e.g., pseudo-breakups). To differentiate between substorm and non-substorm times, we analyzed auroral signatures in THEMIS ASI focusing on properties such as the location and poleward movement of the initial brightening arc. In this presentation, we show results of a statistical study comparing properties (e.g., growth rates, propagation directions) of substorm and non-substorm beads as well as their dependence on geomagnetic indices and solar wind parameters. The presence and characteristics of auroral beads preceding non-substorm events is significant for the identification of their source instability and relationship to the substorm onset process.
Other
Plain-language summary:
Substorms are regular space weather events that explosively release stored energy in Earth’s magnetosphere. This energy manifests in the aurora - enhancing activity in what is known as an auroral substorm. Auroral beads appear as evenly-spaced bright points in the aurora that grow rapidly over the course of minutes. It has been shown that auroral substorms are preceded by beads, and thus, the formation of auroral beads may be tied to the substorm initiation mechanism. However, what fraction of beads lead to substorms is not known. In other words, are beads necessary but not sufficient for the initiation of substorms? We surveyed thousands of images from all-sky cameras and identified over 300 auroral bead events. While a majority of these bead events did lead to substorms, a non-negligible number (10%) were followed by non-substorm events. We looked at the properties (e.g., growth rates) of both types of beads and compared them to indices that track geomagnetic activity. In this presentation, we show the results of this statistical study. We compare our findings to what we expect for different plasma processes capable of forming the auroral beads and investigate the true relationship of auroral beads to the substorm initiation process.
Files
Fall 2024 AGU Auroral Beads Poster - Vincent Ledvina.pdf
Files
(4.6 MB)
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