Not a normally fruitful exercise, but yesterday (27th Feb) a Kp 6 event hit well after sundown, just before a new moon and when the sky was virtually cloudless… Impressive alignment !
Sadly, I didn’t know I’d seen one and until I looked carefully at the above image and noticed an odd green patch near the tree – simply by taking pictures because I was out with the camera anyway meant that I didn’t choose my framing or reduce my ISO as much as I would have if I’d known what was going on. The shot was at ISO 6400, f8 and an 8s exposure, which explains why I didn’t get to see it with my naked eye. The aeroplane light trail was an added bonus too 🙂
So for those of you interested in knowing when to go outside, I can recommend two free resources – the first is the Twitter @RealtimeFlares account which will warn you of solar emissions (look for the X class events like the one that caused last nights’ display: February 25, 2014), but that’s going to be a couple of days ahead of when the particles reach us, even assuming that they were going in the right direction. To help decide if it’s worth heading out to a dark field, then Aurora Notifier is excellent. You can choose the Kp level you care about, it shows an estimated region width during the event, and you can also ensure that you only get the notifications during night hours.
I’ve not looked for an iOS variant of that app, but feel free to add one in the comments/email me.
For a background on Kp, including a rough guide to visibility at various latitudes, then Space Weather Live has a nice intro including the expected event frequency (note that a cycle is 11 years, or 4,017 days (give or take a leap day)).
Finally, for far, far better images, take a look at this BBC News article