On the night of September 3rd, 2019, I may have unknowingly captured evidence of a newly characterized type of aurora know as Fragmented Aurora-Like Emissions (FAEs). On this night, I was about 700 km north of Yellowknife, Canada near Lambert Island sailing the Northwest Passage westbound. The skies were clear, the winds calm, and those aboard our ship were treated to a spectacular aurora display. I attempted to record the aurora by making a timelapse using sequential captures with a Canon 6D and allsky fisheye lens. What follows is some background about FAEs and a description of what I witnessed.
I recently learned about Fragmented Aurora-Like Emissions (FAEs) from an online post by Vincent Ledvina (@Vincent_Ledvina on X). FAEs are a relatively new type of small-scale aurora-like feature that exhibit small horizontal scales of only a few kilometers, short lifetimes of generally less than a minute, and a lack of field-aligned emission extent (Dreyer et al., 2021). Analysis of observations made in Svalbard, Norway in 2015 and 2017 suggest that these features, which show horizontal size typically below 20 km, can be classified into two categories. In the first category, FAEs develop as individual, isolated entities whereas Category 2 FAEs exhibit wave-like structures with regular spacing between multiple emissions that tend to form near and alongside auroral arcs. Spectral analysis showed emissions in the 557.7 nm (atom oxygen green) and 673.0 nm (N2 red) bands but not 427.8 nm (N2+ blue), 630.0 nm (atomic oxygen red) and 777.4 nm (atomic oxygen infrared) leading to an estimated upper limit for the energy generation mechanism of ~8-11 eV. It is believed their altitude ranges between 110-120 km.
The authors of Dreyer et al., 2021 convincingly characterized differences in behavior of FAEs from other known aurora features such as enhanced aurora and pulsating patches due to there apparent dislocation from field lines from adjacent rayed structures (Category 2) and smaller size and short lifespan when compared to pulsating aurora. They offered some suggested generation mechanisms such as Farley-Buneman instabilities, which are streaming instabilities that occur between 90 – 120 km (Oppenheim et al., 1996) which can arise from differences between electron and ion drift speeds which is present during active precipitating aurora activity and the resulting electron heating that occurs with these instabilities and shear.
The post by Vincent grabbed my attention because I personally witnessed some rather strange, small scale aurora features while I was sailing the Northwest Passage across northern Canada in 2019. During the first few days of September, we were treated to clear skies, calm winds and some amazing aurora activity as we headed westbound. This was the first and only time I would witness the northern edge of the northern hemispheric aurora oval as we were at 68º north latitude at the time. On the night of September 3, 2019 I setup a Canon 6D camera at the bow of the ship with a 8-15 mm f/4 fisheye lens set at 8 mm. During early twilight, I set the ISO at 3200 and aperture at f/4 and began a series of sequential timelapse exposures using 5 second exposures. I later reduced the exposure time to 2.9 seconds when the activity brightened significantly. As the skies darkened, faint aurora remained far to the south. However, as the night went on, active bands and arcs snaked their way toward us growing ever brighter. As if curiously inspecting us, they raced overhead to form beautiful coronae. I could make out fast moving magenta fringe from nitrogen emission transitioning to bright green oxygen emission above. Although not really visible to the naked, blue nitrogen light was emitting much higher up the arcs. I was mesmerized as this was the most spectacular aurora I had ever witnessed.
During the brightest activity, I occasionally saw what appeared to be small green dots or marks near some of the arcs that moved quickly in trail of some of the curtains, but was not confident of what I was actually seeing. However, upon processing and viewing the timelapse that I captured, it was clear that there were small “fragments” of aurora present. Although I am an atmospheric scientist that studies lightning, my understanding of aurora and associated plasma physics is limited at best. I, therefore, was just appreciative of the opportunity to witness such an amazingly beautiful aurora display.
Having now been made aware of FAEs and the research efforts to understand this phenomenon, I went back and eagerly reviewed the images I took that night with heightened interest. In conjunction, I read the Dreyer et al., 2021 paper and was shocked at the similarity between my observations and those described by the authors. It became clear, that I very likely captured FAEs that night, although I had no idea what I was seeing. As a result, I intend to make my images available for analysis to those that might find scientific value in them. The Canon 6D has a built in GPS, and as a scientist, I try to always georeference my images and incorporate accurate timing. In fact, I keep all my cameras set to universal time (i.e., Greenwich Mean Time) and either have the GPS maintain the timing or accurately set it each time I format my camera data card after downloading. The images were captured in raw format with camera settings, GPS location and accurate timing embedded in the metadata. Hopefully, this dataset will help to better understand this phenomenon.
Below is the timelapse video from that night during the peak activity and FAE development.
Sources
Dreyer, J., Partamies, N., Whiter, D., Ellingsen, P. G., Baddeley, L., and Buchert, S. C.: Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard, Ann. Geophys., 39, 277–288, https://doi.org/10.5194/angeo-39-277-2021, 2021.
Oppenheim, M., Otani, N., and Ronchi, C.: Saturation of the Farley‐Buneman instability via nonlinear electron E×B drifts, J. Geophys. Res.-Space, 101, 17273–17286, 1996.