Aurora borealis solar minimum ?
Why do we see so much aurora during
Solar minimum at the observatory ?
Last year alone 95% of our guests saw the aurora from September to March regardless of the unusual bad weather. Why did we see the aurora so much during a period when the Sun is supposed to be quiet? Well Aurora borealis solar minimum doesn’t bother us at the observatory !
As you may or may not know the Sun is responsible for the aurora on Earth. In short it sends us highly energetic particles, which in turn get caught in the Earth’s magnetic shield. These particles then get channeled along the magnetic field lines and end up colliding with the molecules and atoms of our atmosphere at the poles. The shock makes the air molecules glow in certain colors like green or purple that we interpret as aurora!
With this in mind there are a lot of factors affecting the creation of aurora, from the moment the particles leave the Sun and till when they create colored light.
Aurora as seen from the aurora borealis observatory this year
The Sun cycle
The Sun actually follows a periodic cycle of activity called solar cycle. A cycle can last for 8 to 14 years but has been averaged at 11 years. These cycles have been observed for centuries because their effect on Earth (auroras among others) is significant.
A peak in activity is called solar maximum. The general activity of the Sun is very high. Its irradiance and the number of solar events have considerably increased. The most notable is the high number of active regions on the Sun’s surface called sunspots and the equatorial location of coronal holes.
They boost the number of flares and CME’s potentially Earth-directed thus enhancing space weather. For aurora chasers it’s rather good news because it means general auroral activity is enhanced on Earth with a higher frequency of displays at mid-latitudes.
Conversely when solar activity reaches rock bottom we call it solar minimum. The general activity of the Sun is low. The disk show few to no sunspots for long periods of time and the coronal holes tend to be located at the poles of the Sun limiting their Earth-directed effect. For aurora chasers at mid-latitudes it’s rather bad news because the number of strong auroral displays is low but we want to stress that higher latitudes still get loads of aurorae.
Solar events and solar quiet
When the Sun has no major activity, also called solar events, we say it is solar quiet. All our star does is to spew a background stream of particles calledsolar wind. This solar wind is always there and is the base for spawning aurora on Earth. Thus solar quiet conditions will give quiet auroral conditions back on Earth.
In contrast the Sun sometimes hosts major solar events that come and break the solar quiet. These events happen more often during solar maximum. We discern 3 major events: Solar Flares, Coronal Holes (CH) and Coronal Mass Ejections (CME). All three participate in enhancing the background solar wind, sometimes blowing huge solar storms out into the interplanetary space. Solar events create very active- sometimes extreme, auroral conditions back on Earth.
Huge coronal mass ejection exploding from the Sun’s surface out into space. This could potentially give exceptional auroras back on Earth. (Photo credits: NASA Goddard)
High latitude and low latitude aurorae
Back on Earth the aurora is produced by very intricate processes. People usually don’t know that there are two distinct kinds of aurora situations.
When there is no major solar event, the solar wind is rather quiet. There might be some sporadic pockets of enhanced solar wind here and there. During this time there is what we call ‘background aurora’. This kind of aurora is produced only at high geomagnetic latitude by a process called magnetic reconnection. It happens all the time and there doesn’t need to be a major input from the Sun for the aurora to appear in the night sky.
On the other hand when a major solar hurling huge numbers of particles towards us, it interacts with our magnetic field so violently that not only high latitudes get aurora via the same process as seen before (albeit more vigorous and long-lasting) but also lower latitudes. The solar storm can penetrate so deep in our magnetic shield that it rattles the inner field lines producing long-lasting, colorful and very active aurorae that can be seen very far from the poles. We call these events geomagnetic storms.
So what about us and Aurora Borealis Solar minimum
The aurora borealis observatory is located at high geomagnetic latitudes (geomagnetic latitude is different from geographic latitude). To be quite precise we are located right in the middle of the auroral zonewhere the background aurora started appearing.
In 2018-2019 we are around solar minimum and we expect way more solar quiet conditions than significant solar events. This season we actually experienced moderate solar events about once a month. Other than that we were back into background auroral activity. The latter still produced many active, local and sporadic solar substorms. This is the reason why our guests have been so fortunate to see many vibrant auroral spectacles this year.
As a rule we saw neat high latitude auroras about 10 times a month…….
This also explains why aurora chasers down at lower geomagnetic latitudes (in the sub-auroral zone, see figure above), are experiencing an ‘aurora drought’ with no significant display for them. So if you want to experience the aurora at all cost, our observatory is deficiently the place to be for the time being!
One of the many colorful auroral substorms ‘exploding’ in the sky over Senja island last season.
Aurora Borealis Solar minimum – Doesn’t bother us at all !