Analysis of Citizen Scientists’ Observations in 2015 Reveals Atmospheric Phenomena

Analyse van de waarnemingen van burgerwetenschappers in 2015 onthult atmosferische verschijnselen

(a) A broad stable aurora borealis (SAR) arc is observed at 09:27 UT (left), a Strong Thermal Emission Velocity Enhancement (STEVE) at 09:51 UT (center), and a partial arc with green wooden fence structures at 10 :02 UT (right). Auroral activity is observed at the bottom (south) of each image. West is on the right; (b, c and d) show decomposed images in red, green and blue colors respectively, at the same time as panel (a). At 09:27 UT (left), no arc is detected in the green and blue channels. At 09:51 UT (center), the three channels detect the arc. At 10:02 UT (right), the main emission comes from the green channel where picket fence structures are observed. A partial arc is also observed in the red channel to the right of the image. Credit: Geophysical Survey Letters (2022). DOI: 10.1029/2022GL098511

A team of researchers from New Zealand, the US and Canada has confirmed the first sighting of a SAR arc evolving into a STEVE. In their article published in the magazine geophysical survey letters, the group describes their analysis of multiple sets of data used to describe the rare and unique atmospheric event and what it showed them about such events in general.

In 2015, citizen scientist I. Griffith noticed something unusual in the night sky above him over Dunedin, New Zealand. An arc of light, which he described as blood-red, moved across the dark sky. Intrigued, he grabbed his camera and started filming the action. Over the next 30 minutes, the arc slowly turned into what has come to be known as a Strong Thermal Emission Velocity Enhancement (STEVE). Curious about what he had seen, he sent what he had caught to the professional stargazers at the University of Otago, also in Dunedin. Also intrigued, the group sent the images to other colleagues. A team of researchers was eventually formed to study the event.

The film shows the entire series of observations, along with undistorted films in red, green and blue channels, respectively. Credit: C. Martinis et al, Rainbow of the Night: First Direct Observation of a SAR Arc Evolving into STEVE, Geophysical Research Letters (2022). DOI: 10.1029/2022GL098511

The researchers collected data from other sources, including satellites and a sky imager at a local observatory. Examining all the data, it became apparent that the first images captured by Griffith showed a stable aurora borealis (SAR) arc, which is a subauroral structure and an event that is not really a Aurora but does exist in the atmosphere for unknown reasons.

The researchers noted that its arrival coincided with a geomagnetic storm— a disruption of Earth’s magnetosphere — suggesting the light was due to charged particles in the upper atmosphere. As the arc started to wane, it turned red to purple, the signature of a STEVE, which is also not very well understood. And then, as the STEVE began to fade, another light appeared nearby, described as a green wooden fence, which has been reported before – and even less known.

The researchers note that all three light events were not auroras, as all three appeared to be the result of locally generated energy, rather than particles coming from elsewhere. They also noted that the event was the first known all three to be seen together.

Mysterious STEVE light emissions emanate from Earth’s magnetosphere

More information:
C. Martinis et al, Rainbow of the Night: First direct observation of a SAR arc evolving towards STEVE, Geophysical Survey Letters (2022). DOI: 10.1029/2022GL098511

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