Hunting for Aurora
All night long...
Aurora on site
We are currently in a period of solar maximum, which is the peak of the solar cycle, characterized by the highest number of sunspots and the most intense magnetic activity. This means that the sun's magnetic field becomes more chaotic and complex, leading to more solar flares and CMEs, which are the powerful bursts of energy and charged particles that can affect Earth's atmosphere and technology. These significantly impact space weather, i.e. the conditions in space caused by the sun. The increased solar activity during the solar maximun means the Northern Lights can be seen more often.
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The Northern Lights, or aurora borealis, are easily visable from the garden and lake directly in front of our cabins, as in the pictures here. Aurora start in autumn and continue on and off throughout winter until spring, being stronger around the equinoxes. Since we are located in the middle of the wilderness, by a large open space and far from city light pollution, the views can be incredible.
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The aurora often form arcs from horizon to horizon and sometimes the arcs begin to twist and sway like curtains in the wind, occasionally expanding to fill the whole sky. The aurora can also take on a more cloud-like appearance, but if you are lucky, they can be seen moving fast and shining very brightly. They are more common around midnight, but can actually appear at any time during the evening and will fade away before sunrise. The picture below shows all of our buildings and the aurora, photographed from our lake with an iphone - the cabin lights are obviously not strong enough to obstruct the light from the aurora!
Hunting for Aurora
The aurora come and go during the night. However, they can only be seen on clear nights and even then, they might only last for a few minutes, so when the forecast is good, it's best to be outside as soon as it gets dark. If the conditions are right, the aurora form a continuous, fluctuating ring, or auroral oval, around the north and south poles, which is typicaly around 200km wide. This oval generally appears between 60° to 70° latitude, and since our latitude is 66°53’53”N, the aurora can be easily seen from our garden. This means that it's not necessary to book an aurora tour elsewhere on clear nights. If it's cloudy, however, and you have a car, you can easily drive around to try to find places without clouds yourselves. ​​​
The Finnish Meteorological Institute has an aurora map here. There are also many apps with aurora activity forecasts that are free to download, e.g. SpaceWeatherLive and My Aurora Forecast. They all use data from satellites, and since it is a real-time feed, they can give accurate predictions for the next 50-60 minutes, depending on the solar wind speed. Look further down the page for help in reading app forecasts. It's also possible to buy an aurora alert service here and you can watch a 4-minute aurora video from Yle TV here.
What are Aurora?
The aurora are determined by the activity on the sun. Space is filled with a constant stream of plasma from the sun called the solar wind. The magnetic field surrounding our planet makes sure we are protected from the solar wind, which carries charged particles from the sun called electrons. These accelerate up to 20,000 km/second along the Earth's magnectic field lines towards the north and south poles. The electrons react with our atmosphere where the magnetic field lines converge and curve down towards the magnetic poles. Here the electrons collide with our oxygen and nitrogen atoms at altitudes from around 1000 kilometres down to 100 kilometres. When this happens, the atoms temporarily get a boost of energy. This energy causes them to release photons, which we see as light. Energised oxygen atoms produce green and red light, while nitrogen atoms produce blue and purple light, thus making the aurora that we see in the night sky.
Aurora Forecast Apps
Here's some things you need to look for with aurora forecasts:
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First, the KP index, which is a measure of geomagnetic activity, where 1 = very little activity, 5 = high activity signifying a minor magnetic storm, and 9 = a very powerful magnetic storm. We are in the KP 3 zone, which means that when the KP index is 3 or more, aurora can be see overhead and in skies to the north. Stronger geomagnetic storms cause the auroral oval to expand up to 1000 km in width, bringing the aurora to lower latitudes. So a higher KP signifies a wider auroral oval, maxing at around local midnight, which means there's a good chance of seeing aurora overhead and in skies to the south when the KP index is over 5.
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Secondly, the speed of the solar wind, which is measured in kilometers per second (km/s) and is normally around 300-500 km/s. However, when there is a hole on the sun's surface, called a coronal hole, the solar wind escapes at a higher speed. The higher the speed, the harder the particles hit the Earth’s magnetosphere, increasing the chances of strong and colourful aurora. A faster solar wind also stretches the auroral oval southwards to lower latitudes, in the opposite direction from the sun. Top speeds can reach up to 1000 km/s.
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Thirdly, the particle density, which indicates the amount of particles coming from the sun. This value is usually given in cubic centimeters (p/cc or p/cm³). When there's a solar flare or an explosion on the sun, called a coronal mass ejection (CME), large amounts of charged particles are expelled into space and are carried along in a solar wind shock wave. The more particles there are in the solar wind, the more chances we get for an intense auroral display, as more particles collide with Earth’s magnetosphere. Again, the higher the better, so near 10 is moderate, over 20 is good, 40 is high, and sudden spikes up to 60 are very high, indicating excellent viewing chances.
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Finally, both the Bz and the Bt values are important measures for auroral activity. During periods of minimum solar activity, the sun only exhibits a dipole magnetic field similar to that of our planet. However, when the sun is more active, additional magnetic fields arch between sunspots on the east-west axis. The state of these magnetic fields (the polarity and strength of the magnetism) is locked into the solar wind as it sets off into our solar system as the interplanetary magnetic field (IMF). The Bz value is the most crucial factor because it indicates the north-south polarity of the IMF: a negative (southward) Bz value, such as -10 nano-Tesla (n-T), is essential for aurora activity because it means the solar wind's magnetic field lines are oriented southwards, allowing them to line up with Earth's magnetic field lines. When the magnetic field lines connect, they open up a rift for more solar energy to enter and pour into the Earth's atmosphere, triggering an aurora. The higher the value, the more active and vibrant the auroral displays.
The Bt value, on the other hand, gives the strength of the IMF: the stronger the IMF, the greater the magnetism! A Bt value of at least 10 nT is above average and over 30 nT signifies a very strong field that can lead to enhanced geomagnetic conditions.
For more science and an aurora tutorial, go to the space weather prediction centre at NOAA
