You can call me 'blob'
There was quite the green display in Northern Ireland last night, one witnessed by loads of people, and one which produced quite a few hollers of delight. But enough about the fact that N. Ireland qualified for the Euros by beating Greece 3-1 last night!
Instead I'm showing you a picture of an unusual aurora feature that I saw for the first time last night. I was listening to the match on 5 Live as I drove to Portmuck and I arrived just after NI scored their 3rd goal. Victory was assured and I got out of the car and set up, happy with the news I'd just heard. Within 10 minutes, and just after the final whistle went for the football match in Belfast, this strange green blob appeared in the sky. At first, fellow photographer Gary Blair and I thought it was an aurora arc poking up from behind a cloud bank. It was very bright and vivid, and with Wednesday night's experience still filling our hearts with excitement, we thought it was the start of something similar.
But when we took some test shots, it wasn't hidden behind cloud. It was a large blob of auroral green, suspended in the sky like some great dollop of ectoplasm. In fact, it started pulsating in the sky - brighter and darker - as it crept from north west to south east. For a few moments it looked like we might have to make a call to our local neighbourhood branch of Ghostbusters to bring a containment box to capture this errant ghost. But, as quickly as it arrived, it faded. And all we were left with was the faintest of green/purple glows on the far horizon.
All that was left was the faintest of green/purple glows far away along the horizon, barely visible even on camera.
I'm not sure what exactly it was. Strangely, Googling 'aurora blob' didn't turn up many meaningful results. When James suggested I Google 'detached pulsing aurora orb', the first result was a 15 page pdf titled, 'Post-noon two-minute period pulsating aurora and their relationship to the dayside convection pattern'!
The after effects of a big aurora storm
A bit more digging around and a few tips from the good folks at Aurora UK seem to suggest that the feature is a pulsating aurora. It consists of patches of brightness, flickering on and off, rather than of an elongated and more long lasting arc, according to some recent research.
Last night I tweeted Dr Tamitha Skov about it, Space Weather forecaster and Research Scientists at The Aerospace Corporation in LA. She is clearly very passionate about sharing her expertise on all things aurora. And, when I woke up this morning, she had answered my question in her Periscope broadcast.
She said displays like this happen as part of auroral substorms, often following a major display like we saw on Wednesday night. As a result of the energy fed in to our magnetosphere by an enhanced solar wind, our magnetosphere is 'all shook up'. And all it takes is a minor disturbance to cause it to kick off some energy as it tries to disperse the energy that has built up due to the solar wind. As it does so, it kicks off little spurts of aurora activity and these tend to be quite short lived (lasting 2 to 10 minutes typically).
The "blob" then could be seen as a residual after-effect of Wednesday night's superb show, a ghostly after-display if you like (sounds like we might need Ghostbusters after all!)
The bar graph shows the global K indices for Wednesday 7th and Thursday 8th, indicating the storm conditions that produced the awesome display on Wednesday. You can see how these stormy conditions continued into Thursday, albeit at a slightly lower level. The graph to the right shows the auroral electrojet for Thursday, with the peaks showing when aurora substorms hit. Around 2200 hours UTC on Thursday, a substorm peak occurred. And this was just about around the time when many of us saw the "blob"
So I have seen yet again the aurora do something new and different for me. And that is one of the many reasons why I love aurora chasing. And it was a lovely way to celebrate the first time our wee country's football team have qualified for a major tournament since 1986!
Thanks, of course, to Dr Skov for her help. But also to all the folks in AUK for helping me get my mind around this wonderful display: Mark, James, Daf, Brian, John, Gus, Kris, Iain, Warren - and all the others. Cheers guys!