It’s been a great couple of days for aurora viewing in the UK. In our second aurora round up, we overview the geomagnetic activity that occurred over the last couple of nights (25-26th Sept) in the UK, along with plenty of pictures from our followers and what we think was the cause.
AuroraWatch UK alert status
On both the 25th and 26th we reached amber alert, meaning that aurora would likely be visible from Scotland, northern England and Northern Ireland and possibly even further south. This occurred at about 9pm UT (10pm BST) on the 25th and around midnight UT on the 26th (1am BST 27th). These were both followed by yellow alerts indicating that geomagnetic activity had died down slightly, meaning you would have had to be quite north in order to continue seeing the aurora.
Cause of activity
The first thing we always do when seeing signs of activity is to check the solar wind data. This is shown below and was provided by NOAA’s Space Weather Prediction Center:
The two pairs of black lines show the time periods where our amber alerts related to. In the first one on the evening of the 25th, we notice a couple of prolonged periods in the topmost panel where the interplanetary magnetic field (IMF) goes negative (or southward). This is a common trigger for geomagnetic substorms (mentioned in our last post, along with some aurora catching tips), and a reasonably average wind speed in the fourth panel makes us believe that this might not due to any other solar activity.
One interesting thing to note is the change that occurs in the second panel during this first interval. You’ll see the blue dots, before this interval, were near the dashed line at 315° but they suddenly drop to 135° at the start of the interval. This panel shows the “phi angle” which is the angle between the interplanetary magnetic field (IMF) vector and the GSE x-axis (a straight line joining the center of earth to the center of the sun). Essentially this sudden change shows that the IMF flipped from pointing away from the earth to pointing toward the earth – which is the result of a Solar Sector Boundary Crossing.
The second event on the night of the 26th and morning of the 27th however is also interesting, but for a different reason. Our previous post gave some details of a coronal hole which caused enhanced wind speeds and thus strong aurora at the beginning of September. Whilst it’s a little too soon to be seeing the effects of that one again (a full solar rotation takes 27 days), these enhanced speeds could indicate the presence of a smaller coronal hole. It takes approximately 4 days for the solar material to get to Earth, so let’s take a look at what the sun looked liked on the 22nd September:
The dark region in the middle is the coronal hole, which because of it’s location would have been outputting fast solar material at the earth head on. This could very well be the cause of the activity spike on the 27th.
Some truly breathtaking pictures have been shared with us over the past few days. Here are just a few of them:
Lady Aurora, the Milky Way and a couple of shooting stars for good measure. #Gress @aurorawatchuk @StormHour @NorthLightAlert @OuterHebs pic.twitter.com/HdAoIIQiqb
— Magz Macleod (@MaggieMacleod) September 26, 2016
And we really like this unqiue way that Kit Carruthers captured the aurora from Almagill Hill in Dumfriesshire, Scotland.
The next few days
Earlier we mentioned about the large coronal hole at the beginning of the month. We anticipated that if it survived, we might be seeing it’s effects again once it rotated around the sun to face us. Well, it looks like exactly that has happened. NOAA has released a geomagnetic storm watch for the next few days, so keep an out for our alerts on Facebook and Twitter and see if you can catch the aurora for yourself!