We got it wrong last night and here’s why

As followers of AuroraWatch UK will undoubtedly be aware, last night was a pretty good night for seeing the aurora from across the UK. As shown in Figure 1, enhanced solar wind speeds, reaching 600 km/s at their peak, were recorded and were the result of a coronal hole high speed stream (you may see others refer to this as a “CH-HSS” or just “HSS”). This high speed, in addition to a favourable southward pointing interplanetary magnetic field, was responsible for strongly disturbing the Earth’s magnetic field and generating a great auroral display.

Figure 1. Data from the ACE satellite, located 30-40 mins upstream of the earth. High speed (yellow) and a southward interplanetary magnetic field (red) lead to strong auroral displays which were visible from across the UK.

Figure 1. Data from the ACE satellite, located 30-40 minutes upstream of the earth. High speed (yellow) and a southward interplanetary magnetic field (red) lead to strong auroral displays which were visible from across the UK.

These favourable solar wind conditions lead many services, who primarily use NOAA SWPC’s data, to issue alerts of aurora visibility. As shown in Figure 2, the estimated Kp index, a measure of the planetary geomagnetic disturbance, peaked at around 7 (out of a possible 9). This is an elevated level which suggests that an aurora should be visible from across the UK. It is important to note, however, that this is only an estimate and that Kp cannot be truly measured in real-time and is not a very good indicator for aurora alerts.


Figure 2. NOAA SWPC’s estimated Kp index. The Kp index reached its peak of 7 at 9-12pm (UT) on 06 March 2016.

Additionally, as shown in Figure 3, the OVATION Prime model predicted strong auroral displays with a very good chance of an aurora being visible from the UK. So with these favourable conditions and promising signs from other aurora services, one might expect that AuroraWatch UK would have issued strong indications of aurora visibility too.

Figure 3. The SWPC OVATION Prime (2010) output for 10pm (UT) on 06 March 2016.

Figure 3. The SWPC OVATION Prime (2010) output for 10pm (UT) on 06 March 2016.

Unfortunately, we didn’t.

What went wrong?

Well let’s first start by saying our magnetometers did record geomagnetic activity and throughout the night our alert level was at “Yellow” status. As shown in Figure 4, from around 5pm (UT) until the early hours of the morning, the AuroraWatch UK status was “Minor geomagnetic activity” which indicates that “Aurora is unlikely to be visible from the UK except perhaps the extreme north of Scotland”.

Figure 4. The AuroraWatch UK alert status and geomagnetic activity plot for 06-07 March 2016.

Figure 4. The AuroraWatch UK alert status and geomagnetic activity plot for 06-07 March 2016.

Clearly, however, we got this wrong. The aurora was seen from right across the UK which suggests that we should have at least issued an amber alert “Aurora is likely to be visible from Scotland, northern England and Northern Ireland” or perhaps even a red alert “It is likely that aurora will be visible from everywhere in the UK”.

The main thing to know is that we issue alerts based upon real, measured data. We do not issue forecasts and we do not speculate about what might happen. Our alerts are 100% based on the difference between our recorded magnetic field data (black line in Figure 4) and our “quiet day curve” (blue line in Figure 4). A quiet day curve is an estimate of the geomagnetic activity on a quiet day, i.e. when there is no elevated activity. This estimate changes throughout the year based on many different variables, including temperature at the magnetometer site.

The difference (dH in Figure 5) reached a maximum of 99.4nT – just 0.6nT below the 100nT amber threshold. We were exceptionally close to issuing an amber alert. Unfortunately, we have a threshold set in our code and we just didn’t quite reach it.

Figure 5. The maximum dH reached 99.4nT, just 0.6nT from the 100nT amber alert threshold.

Figure 5. The maximum dH reached 99.4nT, just 0.6nT from the 100nT amber alert threshold.

Lessons learned

There are a few things we could do differently, however, and these would have generated amber alerts. For example, if we measured the difference between the maximum H and the minimum H (a measure of the Earth’s magnetic field in the geographic north-south direction), we would have recorded a change in excess of 140nT and this would have generated an amber alert. Additionally, if we’d set our amber threshold a little lower (e.g. 90nT) then we would have generated an alert too. Or perhaps if we’d tweaked our quiet day curve, we’d have recorded a larger reading then also.

We also note that the data above was recorded at our Lancaster station, which is the primary station we use to generate our alerts. However, had we shifted to using data from our Crooktree station (located near Aberdeen) we would have measured a slightly larger disturbance and generated an amber alert.

So, yes, there are a few things that we could have done differently and on this occasion any one of them would have resulted in us issuing an amber alert. The problem is that the AuroraWatch UK systems are all automated and so it takes events such as these for us to determine how well this automated system is working.

Rest assured we didn’t like missing this alert any more than you. We are going to be looking into this event further and we will be making changes in the near future to help prevent us missing events of this kind again.

44 thoughts on “We got it wrong last night and here’s why

  1. As an avid follower of AW and living on Skye I can say that the Crooktree location was very accurate to what I saw in terms of Aurora. Lancaster is far weaker and in reality does not represent what is actually visible here in at 57.North.

    • I left Skye 8yrs ago and must admit to being a bit blasé about Aurora’s after living there for many years. Now I’m living near Carlisle it’s so exciting even just the faintest chance of seeing it again !! Last night I saw them purely by chance, no where as good as Skye, but it made me happy 🙂

    • But is probably as accurate for people living around Lancaster as Crooktree was for you. 🙂
      Maybe they need to take a mean measurement from both stations and this may give happy medium figure?

    • Hi,
      We are going to Skye this weekend – carbost. Would you recommend anywhere in particular in Skye that’s good for sightings?
      Many thanks

      • Hi Marie,

        The far northwest side as well as the very southeast of Skye are both dark sky areas. You can learn more about this here: http://www.darksky-skye.com/ I stayed in the Ardvasar Hotel last summer in the southeast – too light in the summer for aurora watching but the hotel was comfortable and the town (Armadale) is quite small so I’m sure it would be quite dark without having to go far at all. Good luck, I’m still hoping to catch my first aurora, but I have to get out of light-polluted Glasgow first!

      • Uig Hotel, in Uig was where we stayed last week, and it was fantastic, with views out over the bay towards the setting sun. The road from Uig over to the Quairang is great for dark skies and 360° viewing – good luck though, we had cloud cover and snow showers every night!

  2. Perthshire, with the AW app on my iPhone and iPad, and yet another missed aurora 🙁

    Hopefully next time.

  3. You guys do a fantastic job of keeping many followers informed. Keep up your great work. .. you had a slip up … so what … everyone knows it wasn’t intentional. Let the grumps try to do your job

    • I agree and think it’s not very often people admit, in public, they inadvertently made a mistake and then say how they’ll do what they can to rectify the situation; you are to be commended for your honesty, integrity and skill….many could learn from this. I appreciate your excellent information stream.

  4. I did wonder why I hadn’t seen anything from you guys on Facebook. Maybe you need to also keep up to date with hashtags on Twitter and Facebook as there were loads of photos and statuses appearing about the aurora from just after 8pm last night in the Aberdeen area, including one that I managed to catch on my mobile phone while out walking my dog in a built up area. Hats off to you though for admitting your error and perhaps rely more often on your Aberdeen location seeing as we are much further north than Lancaster.

  5. To echo previous comments – fair play and thanks for the clear and unambiguous explanation. Hindsight is always a marvelous thing, and software can only do what it is programmed to do and will always need tweaks and changes as lessons are learnt. Anyone who thinks otherwise has never written code! Keep up the good work

  6. Thanks for the explanation ..disappointing to miss it but I saw pictures posted from Cromer in Norfolk
    I follow avidly and will get to see a good one one day I’m sure

    Jim Norfolk

  7. Thank you for that very detailed explanation – I have been puzzled all day over the non-alert and that explains it very thoroughly. Many thanks for all your previous alerts and here’s to many more.

  8. When I signed up to Aurora watch alerts, I read how you calculate them and how they work. I live in southern Scotland so what I tend to do when you issue any alert, even of yellow, is keep an eye on the charts, check the cloud forecast, then look at where other people have seen them. This worked perfectly for me last night and I got to see an amazing display, which I wouldn’t have been aware of if it weren’t for you.

    Horrible to see other people ‘blaming’ you for their inactivity on social media, and I feel people should take more responsibility for themselves, especially when using a free service. If I used some of the other services, I’d probably have a lot of wasted evenings not seeing the lights when they get their predictions wrong – though I still wouldn’t give them a hard time, it’s just down to the different ways of recording, reporting and predicting.

    • Totally agree with Anna,I got the same alert,then checked other sites and got an accurate time of when it was visible where I live…Was an amazing display which I would not have known about but for the Aurora Watch alert,so thanks guys..

    • Can anyone recommend other things I can also check I use the app but missed it but I will say you admitted there were errors but hey nobody is perfect

  9. Interesting article, thanks for the explanation. Living in Edinburgh & Perthshire for 50+ years, I’ve never seen an aurora. Living in hope.

  10. chill 🙂 everyones human 😀 maybe thou a manual over ride would be good… ie if enough ppl reported sightings then you automatically issue an alert regardless of what equip and algorithms suggest..

  11. It was very disappointing not to get an alert, which I always respond to by going out to have a look! We are in the north of Scotland but have to drive round to the other side of our big hill. By the time I saw people talking about it on Facebook last night, I had sadly had a drink or two with relations from the south who were staying with us, and we could not drive anywhere. So sad as they have never seen the aurora. In the south you don’t really expect to – it is us in the north who are always hopeful, so it would be good to get the data from the north instead of Lancaster. Hope we get another one soon anyway.

  12. I was out gritting all over Scotland and what a light show dancing in the sky. Hoping there might be some more of the same tonight

  13. You are wonderful people and we are more than fortunate to have these alerts …. Thank you for your detailed explanation and no harm done at all.
    God bless you all xxxx

  14. is it likely we’ll see anything from the NW of UK tonight please anyone? Thanks

  15. Was sorry to miss the display and wondered why we hadn’t had the alert – this explains it well. I was in Norway and saw the lights last month but even there they admit that it is incredibly hard to predict if – where – when Aurora will put in her appearance. Hopefully another time 🙂
    Thanks for a great service!

  16. Keep up the good work, last night will only assist in you further improving an excellent free service

  17. Good explanation. I’m lucky enough to have seen the Aurora on a few occasions, and this site and it’s notifications have helped me pick the right nights to go out and try to view it. I thought there was a problem with my Facebook account when I heard we’d missed a chance. It’s great that you have taken time to explain how it all works, and also how you are looking to learn from it so that future forecasts improve.

  18. Thanks for the post-mortem & props on your work.

    Can I also suggest another tweak: Put in your postcode/read-the-users-GPS-data-in-the-App and get an alert which weights the Crooktree & Lancaster measurements accordingly. A bit like the BBC.co.uk/weather/{XYnnNabPostcode}

  19. Hi, I’m in the North of Ireland, Co.Antrim, what an amazing display we had,so not to worry. Just had to open my front door and look up, wow!! I’ve been on the look out for a while and even went to Iceland but didn’t see them there, so it was truly very special and I’m keeping your app (which I think is very good) just in case I get another chance to see them again.

  20. Really good to see the hands up approach and explanation- can imagine you were as gutted as I was, as I only look for your alerts. I spent Sunday evening in my camper van with the blinds down reading…. sobs.

  21. Excellent explanation. I went to Finland to see Lights a month ago and failed, yet on one night the viewing was fantastic. Locals and experts said there was too much cloud and the lights would not be visible so the tour was cancelled so we all missed a fantastic display; this just illustrates how predicting displays can be so difficult.
    I think your app is fantastic and I have hopes of seeing the NL’s one day.

  22. I live in Hertfordshire – didn’t get al alert and didn’t see anything.
    I want my money back!



  23. Well at least lessons were leaned and to be honest you do a great job thanks

  24. Thanks for that, I understand your logic and got lucky that a friend monitored swpc-noaa-gov and we saw a fantastic display from Northumberland. I’ll monitor both sites in the future for best potential viewings.

  25. Pingback: Did I photgraph the aurora or was it something else? | AuroraWatch UK

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