An old school aurora chase

One of the things I’ve tried to do since I began my journey as an aurora chaser is to teach myself how to read the stats. There is a wealth of information out there that can help shorten the odds and increase your chances of catching the dancing lights. 

But sometimes I wonder what it must have been like in (as my kids used to say) the “olden days”. You know, in those dark ancient times known as “BI” (Before Internet). It must have been largely down to luck – and that other quality that can shorten the odds: perseverance! 

Last night didn’t quite take my all the way back to “BI”. But, for much of my chase, I was without phone signal. So it was old school observations: trying to get a feel for what was about to happen based on nothing else than sky observations.

Stats of potential

As we approached the hours of darkness, while I still had internet access, the stats started to look interesting. The Bt (the strength of Interplanetary Magnetic Force, or IMF) rose to a very impressive 20nT. The Bt acts as a cap to the Bz values, so with Bt as high as this, it meant that should the Bz drop to negative, it could potentially go quite far down – a great thing for the aurora. Also, the density rose, then fell again – a possible indication that the bow wave of the anticipated CH HSS was pushing towards the earth. And when the speed of the solar wind rose, this was another good sign that the HSS was here. All that to say: there was enough happening to tempt me out, especially as we had glorious clear skies (following on from the most spectacular of sunsets that afternoon). 

The chase begins...

I had though that Woodburn Reservoir near Carrickfergus, Co. Antrim would be a good aurora viewing location. On still nights, you can get wonderful reflections on the water’s surface. So I headed there, and met up with my good photographer buddy, Gary Blair. The night was dark, the stars were out, and we were all set. We set up our cameras and, lo and behold, there was something appearing faintly on screen already. Looked like we were going to be in for a show.

The only problem we quickly discovered was that phone reception is very poor in that location. No chance of checking the magnetometers for those all important hints that things were about to kick off. No chance of field reports from fellow chasers in Aurora UK. This was old school chasing (albeit with digital cameras and a great update on stats just before we headed out!) and it would be a good test of how well we were able to read the signs by our eyes alone.

There were some things against us: the aurora display was a relatively understated affair; and there was a bright crescent mooing shining in the sky and washing out the show. But, undaunted, I set up for a time lapse and Gary and I peered into the night sky while having a good old natter.

Then, just before 9.30, we were sure we saw a brightening of the sky along the horizon. I was even convinced I could see a faint green tinge (although that could have been wishful thinking!) Often, before an outburst of pillars, the green band will grow in intensity. We had no stats to check: but we could feel it in our bones that something was on the cusp of happening. 

And indeed, not too long afterwards, it did! Faintly visible to the naked eye, rays began to appear. Cue the usual hollers of delight from Gary and me – it’s always amazing to see the sky spring into life during an aurora event, even in more subtle ones like this. The active period turned out to be short lived, but we had got it!

We stayed on for about another 45 minutes or so, during which time Gary made the most delicious lattes on a camping stove, and I finished off my time lapse shots. Then, it was time to call it quits, and we headed home, happy that we’d bagged another aurora.

Checking back on the night's stats

When I got home, I immediately checked the stats. The density had indeed continued to drop, and the speed had built – both signs that the HSS had probably impacted. The Bt dropped down to around 10nT. And the Bz, although it didn’t settle into long periods of southerly orientation, dipped down to negative values off and on up to around 22.00 hours. Clearly, these things had been enough to prompt some action. 

And the magnetometers confirmed that. Around 21.30 hours, they started to react, with some quite good movement, and that movement extending quite far south. This corresponded to the period of activity that Gary and I had witnessed – and that we had predicted by eye just before it happened!

When out hunting, I’d always prefer to have access to the stats. Information is power, and all that. But it was encouraging that we’re picking up enough field experience as aurora chasers to allow us to get a good gut feeling for when things might kick off. Old school chasing was fun – for a night!