Bright Aurora and STEVE on the 5th November 2023

On Guy Fawkes night at the beginning of this month we had an excellent display of the northern lights here in Norfolk and this is only the second time I have seen this phenomena in my lifetime (the other time was in Edinburgh in the early 2000's). The lights were triggered by a strong G3 geomagnetic storm caused by two Coronal Mass Ejections (CMEs) from the sun which arrived on the 4th and 5th November. As you will see from my report below I ended up being more interested in an associated phenomenon called a STEVE which was more noticeable than the aurora itself (follow the link to see more about what a STEVE is).

Here is my report that I sent to the BAA Aurora Section:-

"Having received an alert from the AuroraWatch app on my phone that the Geomagnetic activity at Sumburgh Head had reached over 600 nT at about 1700 UT I went outside to look at the sky about 18:35 UT. The sky was dark by then (Astronomical twilight ended about 18:20 UT and the Moon, at last quarter, hadn't risen). The first thing I saw was a band of milky white light quite high in the sky to the north. Being unclear whether I was seeing some sort of cloud or an aurora, I went to grab my Nikon D90 DSLR and the first picture I took was at 18:42:12 UT (see below). This showed the band of white light curving down towards the eastern horizon and passing though the constellation of Perseus. To the right of it in the picture is a patch of glowing red light.

This I took to be confirmation that this was an aurora and not a cloud formation and I have subsequently learned that the white light is called a STEVE, which is an associated phenomenon. Having only seen an aurora once before in my life, I found myself concentrating on aspects of the STEVE and perhaps neglecting the more commonly observed green dome of light due north.

 

What I thought was important about the arc of white light or STEVE was that it was a complete arch running from the eastern horizon right across the sky to the western horizon. My second picture (18:43:54 UT - see above) shows the arc passing above Polaris near the centre (but slightly to the right) of the frame. I have identified 76 Draconis as a star (at RA 20h 42m 35.0s Dec +82d 31m 52s) near Polaris which sits roughly in the middle of the arc and using software (using the date, time and my location) I have determined that this star was at an altitude of 59 deg. 44 min. So the arc most likely reached about 60 degrees in altitude due north. In my picture, the arc appears to slope further up to the right. I have confirmed that this is because in my haste my camera was not set level. I found that another star located in the arc to the right of polaris (48 Cas RA 2h 1m 57.3s Dec +70d 54m 26s) was at an altitude of 57 deg 6m.

Going back to the picture I took at 18:42:12 UT, by projecting the direction of the line of the arc towards the eastern horizon on a star map it seems that it would pass close to 47 Tauri (RA 4h 13m 56.4s Dec +9d 15m 50.0s) and at this time and location this star was at an altitude of 3 deg. 24 min. and at an azimuth of 78 deg. 46 min. measured eastwards from the north point. So it is likely that the STEVE intercepted the horizon at an azimuth of about 79 degrees (but it could be a little less than this if the arc was still curving inwards towards the north).

By 18:50:57 the white arc of the STEVE had dissipated leaving only a red glow in the eastern horizon as seen in the picture taken at this time (see above). However, after this time its strength grew again as can be seen in the images taken at 18:54:47 and at 18:56:19 (see below) and the arc was again a complete arch across the sky.

During some of the time when I the STEVE was at full strength I noticed that it appeared to be flowing from east to west along the white arc. This was evident by the fact that there were bands moving quite quickly along the arc (lines of brighter intensity with a direction perpendicular to the line of movement) and I was surprised by how fast they were moving.  I would say that they covered about 15 degrees of arc in a few seconds (so may be 7 or 8 degrees per second). 

My attention then turned to the western horizon and the picture taken at 19:00:43 shows this (see above - note that here I had increased my exposure time from 15s to 30s; see my note below about my camera settings). Although there is some evidence for cloud to the left of this picture, the white arc of the STEVE and the red glow (now to the left of it) is very much in evidence. You can also see the green glow of the aurora to the right towards the north above some television aerials. What is ineteresting to me is the symmetry of the STEVE display. What is seen in the west is a reflection of what is seen in the east and they were happening at the same time. 

By about 19:02 UT the STEVE began to dissipate again and so the part of the display I had seen lasted about 20 minutes. At 19:03:56 I took a picture towards the north (above - actually slightly east of north) at a lower elevation which shows the green and slightly red light of the aurora in that direction. At 19:08:14 the red glow in the east associated with the STEVE could still be seen. I went in for my dinner around this time but I came out again about 20:00 UT to take some more photos. Some greenish tinge low in the sky could still be seen to the north at 19:58:15 UT.

A note about camera settings. All pictures attached to this report were taken on a Nikon D90 with a Nikkor VR 18-105 f/3.5-5.6 ED lens. The settings were a focal length of 18mm, ISO3200 at f/3.5 giving a field size of 66x46 degrees approximately. Up until and including the picture taken at 18-56-19 UT the exposure time was 15s. After that it was 30s."

All text and images © Duncan Hale-Sutton 2023