Update #5 (09:00 UT, 13/9/14):
A frustrating geomagnetic storm.
After a brief flurry of activity which saw aurorae becoming visible as far south as the middle of the UK, the Netherlands and northern Germany (and even then, not massively strong – moonlight didn’t help), the direction of the interplanetary magnetic field swung sharply northward, and remained north. This unfortunately has the effect of dampening out any auroral activity, restricting any displays to the polar regions.
What’s really unfortunate is that this was a very, very strong CME – if the IMF had stayed southwards, we would have seen an extremely strong auroral display, reaching as far south as perhaps Spain, the middle of the US and as far north as maybe southern Australia, a once per solar cycle event. Oh well. Sadly par for the course with mid-latitude storms in Cycle 24 – all have been a fizzle.
Here’s a gallery of pictures taken by observers in the UK, and collated by the Aurora Watch UK team. Likewise, photos from the NOAA Aurora Spotters group.
We still are in the effects of the CME, right in the middle of the core, which alas is pointing strongly northwards. The polarity may change southwards once we leave the core, but it’s wait and see, and no guarantee that we’ll have any decent activity tonight in Europe. We’ll just have to wait and see….
Update #4 (19:50 UT, 12/9/14):
G2 geomagnetic storm level.
The Kp index remains at 6, so we are still within a G2 storm level. However, Bz remains stubbornly pointing northwards, so aurora are not visible further south as yet. Still, it’s early and darkness has now arrived in western Europe. Those in northern Scotland and Scandinavia should keep an eye out.
Update #3 (17:50 UT, 12/9/14):
G2 geomagnetic storm level reached!
NOAA reports that the Kp = 6 threshold has been reached – we are now at the level of a G2 geomagnetic storm. Keep an eye out after dark for auroral activity!
Update #2 (16:15 UT, 12/9/14):
CME arriving at the ACE spacecraft!
The NASA ACE spacecraft has detected the 2nd CME en route – the CME is now roughly 30 mins from arrival at earth. Dynamically updated plots available here. We are still in quiet geomagnetic conditions (G0), though this is expected to change. Bz is slightly pointing southwards.
From NOAA: “The second of the expected coronal mass ejections (CMEs) has arrived, and arrived in good agreement with the predicted arrival times (shown here in this ACE solar wind plot as the strong discontinuity near the end of the graph). As expected, an initial looks shows this CME is stronger than the first. More to come as this event plays out but the forecast for G2 (Moderate) storming for September 12th and G3 (Strong) storming on the 13th still looks to be reasonable. The solar radiation storm that is in progress as a result of the eruption on September 10th has increased with the passage of this shock, as it often does, and we currently sit just above the S2 (Moderate) threshold.”
Update #1 (15:45 UT, 12/9/14):
CME arriving!
NOAA is reporting a shock passage at 1530 UT, which indicates that a CME arrival is imminent. The solar wind is picking up in speed (around 670 km/s), and there are now warnings that a Kp value of 6 is expected within the next 3 hours.
Original post
The current solar cycle (the 24th since extensive monitoring of sunspots began in 1755) has been extraordinarily weak: there have been fewer sunspots and solar flares than in recent cycles, with a corresponding lack of strong displays of the Northern Lights (also called aurorae) visible from the more heavily populated middle latitudes (such as northern Europe, southern Canada/northern USA). Indeed, I struggle to recall any very strong displays that far south – a combination of bad luck with cloud and the wrong polarity of the interplanetary magnetic field (IMF) have nulled any potential for good displays during this solar cycle.
However, good news! The Sun has woken up in the last few days! An active sunspot region on the Sun has erupted twice with strong flares this week – in the nomenclature of solar flares, a M-class (moderate strength) on Tuesday and a X-class (strong) flare on Wednesday. What’s even better that both flares ejected plasma and high energy particles (otherwise known as a coronal mass ejection, or CME) directly towards us, and it is this material that will trigger geomagnetic disturbances that, hopefully, will allow us to see the aurora at more southerly latitudes.
What are aurorae, and why do we see them?
So first of all, I hear you ask, what are aurorae and what triggers them?
Aurorae are produced when highly energetic particles collide with and excite the atoms and molecules of the Earth’s upper-atmosphere.
These particles, protons and electrons, are of solar origin and travel via the Earth’s magnetic field to form two permanent rings of auroral light centred around the magnetic poles.
The so-called ‘auroral ovals’, during quiet solar activity, are located at arctic latitudes – too distant to be seen from the UK and similar places far to the south. However, following intense solar events (like the ones this week) and the subsequent enhancement of the solar wind, the auroral ovals, under certain conditions, will expand towards the equator.
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It is at such times that auroral displays are seen at latitudes such as the British Isles and northwestern Europe. I should state that the auroral ovals are ‘fixed’ in position – they surround the geomagnetic poles, and it is the Earth that rotates under them rather than them themselves rotating, so we are closest to them at the same time every night.
In central Alaska or northern Scandinavia, on most nights you can expect to rotate directly under the oval in the midevening hours, be inside it (poleward of it) around midnight, and pass under it again before dawn. Thus one expects to see the aurora move from the northern sky shortly after dark, to overhead at midevening, and to the south around midnight, then back overhead again in the early hours of the morning.
In the UK and Ireland, we are closest to the ovals at around 22:00-23:00 GMT – magnetic midnight – and usually this time is the peak of activity during storms (though there are additional peaks during storms, depending on the storm intensity).
Being so closely linked to solar activity, the aurora reflects the changing nature of the solar cycle. Generally, it can be said that more aurorae will be seen from southerly latitudes over the few years around solar maxima. During a rare large storm, the oval may expand so far toward the equator that it can be seen from the tropics, while skywatchers at midnorthern latitudes actually find themselves facing south.
So, what should we expect?
To give a little background on the flares and incoming CMEs (and the likelihood of seeing aurora on the 12th/13th, here’s a rather nice space weather forecast by Tamitha Skov, a scientist at The Aerospace Corporation in Los Angeles, California (you can also follow Tamitha on Twitter: @TamithaSkov)
Tamitha mentions that the storm will be a G3 one in intensity – this scaling system is from the NOAA Geomagnetic Storm scale. So it is expected to be a moderately strong storm, as it currently stands (G5 being the strongest).
OK, so what about the timescale? When will this happen?
As I write this now (~11:00 GMT on the 12th), the first of the CMEs has arrived, giving us a glancing blow – we are currently in the lowest of the NOAA storm scales, G1, and activity is still confined to the polar regions. The 2nd CME is due to hit at some point in the afternoon GMT on the 12th, according to space weather models. The arrival of the second CME is expected to push it up to the G3 level – it’s a strong CME and it is fast, a very good sign – and if that happens, and the polarity of the magnetic field in the z-axis (Bz) points southwards, then we are in for a treat.
OK! So, how likely am I to see the northern lights?
Of course, the closer you are to the auroral ovals, the better your chance of spotting the aurora. However, the more intense the geomagnetic storm is, the better your chances are at your location to spot something.
You will see that the index Kp is mentioned on the NOAA scales – this is a index of the strength of the magnetic disturbance, with a scale of 0 to 9, with the higher the value, the stronger the aurora. Generally, we need at least a Kp value of 6-7 to see aurora from Ireland and the UK, southern Scandinavia, New Zealand (which is generally what you get with a G3 level storm), and higher the further south you are (north in the Southern Hemisphere) – a G4 or G5. To illustrate what Kp value is required to see the aurora from your location:
Europe
North America
Australia/NZ and southern Africa
So, if we do get a G3 storm, I’d expect the potential for spotting aurora across Ireland and the UK, northern Europe, the northern half of North America and most of New Zealand. If we are lucky, and the direction of the z-component of the interplanetary magnetic field goes strongly south, the storm will intensify, and those further south will get the chance to spot the northern lights.
What’s the best way of keeping informed of the likelihood of a strong geomagnetic storm and auroral display?
You can keep an eye on various sites that track geomagnetic/auroral activity, or use apps on your smartphone or tablet. Here are some sites to monitor for real time geomagnetic conditions:
The NOAA Space Weather Prediction Center
SpaceWeatherLive.com – excellent European volunteer-run site, good updates & analysis.
The British Geological Survey Geomagnetism Group
Aurora Watch UK – run by Lancaster University in the UK.
NOAA OVATION auroral oval model, with maps to estimate the current extent of the auroral oval.
AuroraMAX – watch the Northern Lights live from Yellowknife, Northwest Territories, Canada.
For smartphones/tablets, I recommend the following apps to keep you up to date with auroral conditions and solar activity (I use them myself):
Solar Monitor (for iPhone and iPad)
Aurora Alert (Android)
Both apps are pay-for, but well worth it.
How do I observe the northern lights, assuming there’s a strong display? What should I expect to see?
Find a spot away from street lights and a good view of the northern horizon (southern if in the Southern hemisphere). In Ireland and the UK, I’d expect a peak around 2200-2300 GMT (at magnetic midnight), but activity, if strong will continue throughout the night. This timescale will vary dependent on when the 2nd CME arrives at Earth (it takes a few hours after CME arrival for the aurora to get going – and should hopefully enhance any activity from the 1st CME).
Be patient – auroral activity can be highly time variable, so just keep looking north.
Obviously, places with a lot of light pollution will have a hard time spotting the northern lights. Try to get somewhere dark if you can.
It really is a wait and see approach – there are no guarantees that we will even get a good display! If Bz points north, this has the effect of dampening out any geomagnetic disturbances, so the auroral ovals do not expand, so no aurora.
We also have two additional enemies: cloud (of course), and a bright waning gibbous moon (80% illuminated). However, you can spot aurorae in bright moonlight, but the display has to be a strong one. Only way to make certain is to look!
So, if we do get a strong display, what should you expect to see?
The following notes describe each of the most commonly seen auroral forms. This is taken from the Society For Popular Astronomy website:
| Glow (N): | The first sign of impending auroral activity is normally a faint glow of light lying low on the northern horizon. Auroral glows are similar in appearance to faint twilight conditions, and can easily be mistaken for the light of a distant town or city. |
| Veil (V): | Bright and active displays can produce a background veil of auroral light covering a large area of sky beyond the main parts of the display. |
| Rayed Arc (RA): | Formation of a rayed arc occurs when vertical columns of light project upwards from a homogeneous arc. Rayed activity often follows sudden brightening of the arc. Again, obvious folds or kinks may be present forming a Rayed Band (RB).Auroral Rays (RR) can also be seen in isolation, stretching up from the horizon in the absence of other obvious activity. This represents the uppermost parts of a display, the remainder of which is being masked by the observer’s horizon and would be much more impressive from a more northerly location. Auroral rays mark the position of the Earth’s magnetic field lines and can extend up to several hundred kilometers above the Earth’s surface. |
| Patches (P): | Commonly seen during the declining stages of a display are isolated patches of auroral light. Like arcs and bands, patches can be either homogeneous (HP) or rayed (RP). |
| Homogenous Arc (HA): | As an auroral storm pushes southward it gradually assumes more definite structures. The homogeneous arc is a rainbow-like arch of light – often green in colour – seen only a few degrees above the north point of the horizon. At times the arc may form twists or kinks, in which case the structure is described as a Homogeneous Band (HB) |
| Corona (C): | Very occasionally the aurora may push into the southern half of an observer’s sky. When this happens perspective effects cause rayed forms to appear to radiate from a single point close to the zenith. This point represents the magnetic zenith which from UK locations lies 18–25 degrees south of the true zenith. Formation of coronal activity often precedes a decline in activity. Thereafter the aurora will fragment and retreat northward. However, on very rare occasions the aurora can penetrate south of the UK and push over the southern horizon. |
Some images of the above types.
Auroral veil
Rayed arc
Patches
Homogenous arc
Rays
Corona
A note on the colours above – the energetic particles smacking into our atmosphere are exciting molecular oxygen, which is what causes the white/green colour of aurorae, and this is indicative of the lowest level of excitation. As the storm become more energetic, we move to higher state of molecular oxygen being excited – so we see yellow and red aurorae. Finally, if the storm is severe, we see nitrogen being excited – so you may see blue aurorae!!
If you wish to photograph them, almost any camera―either digital or film―will work for photographing the aurora, as long as you can adjust it manually to take time exposures of 10-30 seconds or longer. An all-automatic camera may not work well for these photos, I’m afraid, but it’s certainly worth trying.
Digital cameras do a great job if you can set them for a fast ISO (200, 400 or faster). Cold temperatures will sap battery strength, so carry spare batteries in a warm place, such as an inside pocket. And don’t worry about using a light meter; it usually will only work for your daytime photos!
Nearly any kind of lens will work for aurora photography but, since the aurora can cover huge areas of the sky, a wide-angle lens would be a much better choice. Equally important is that the lens be as ‘fast’ as possible (i.e., have a small f/ratio like f/2.8, f/2 or smaller). Without a fast lens, exposures will need to be longer, and that will tend to blur the aurora more.
Footnote
Finally, some reminiscing! I spotted my first aurora in 1991 – and I was lucky to see the huge auroral storm of Nov 8/9 1991, where the storm was so intense that the aurora covered the entire sky at its peak with blood-red light, with a glorious corona!!!!! No wonder it used to frighten our ancestors.
It was one of the most amazing things I’ve ever seen. Fingers crossed for a repeat this weekend. If you get the chance, go out and look! You won’t regret it.
Clear skies and best of luck!