Polar Lights at Valkea Lodge, Pello, Finland, 28 February 2019

Polar lights are not related to meteors but are beautiful to view anyway. I spent a week of holidays in the Valkea Lodge in Pello, Finland, close to the swedish border and to the polar circle. As the sunspot cycle approaches the minimum, the sun without sunspots for many days in sequence, I did not have great hopes of seeing any polar lights. So I did not take special equipment with me for recording it, only a compact camera (Canon G11 PowerShot). The more surprised I was to see these beautiful northern lights which started in the evening and lasted for most of the night, although at lower intensity. During the vacation I had a polar light alarm by the travel agency and the forecast by https://www.spaceweatherlive.com/de/aurora-alarm. These indicated a good chance to se polar lights on the 27 and 28 of february, caused by a coronal hole facing earth (https://www.spaceweatherlive.com/en/news/view/373/20190224-coronal-hole-faces-earth-g1-watch). On the 27 the weather was clouded, but the forecast for the 28 was good and the polar lights started intensly right after dinner.

Observation

I used the camera on a tripod, equipped with a home-made remote release shutter in continuous mode with the following camera setting

  • f: 6 mm,
  • F: 1/2.8,
  • ISO: 1600,
  • exposure time: 1 sec,
  • 2.4 sec/image.

For the time lapse video, the images were binned 2×2 and a caption with the time added with IrfanView, converted and edited with VirtualDub and finally converted to mpeg with XMedia Recode. The speed is about 25x real speed:

The polar lights lasted much longer than the video, at some point the camera batteries gave up in the cold (about -15°C).
Here a summary of the whole night from the all-sky webcam at Valkea Lodge from the same date:
(copied from http://www.kontiki.ch/nordlicht-pello)

Coronal hole

Polar lights are associated with charged particles streaming from the sun at velocities of the order of 500 km/sec. There are mainly two sources of charged particles:
– coronal mass ejections
– coronal holes
Coronal mass ejections are related to sun spots and area of high activity on the sun. At present we are close to the solar minimum, with weeks on a row without a single sunspot, therefore coronal mass ejections are rare.
Coronal holes on the other hand can occur any time but are more frequent during low activity of the sun. If a coronal hole is located near the center of the solar disk and faces earth, charged particles may leave the sun along open magnetic lines. The image below shows the sun at a wavelength of 193 A on the 25th of February. The hole is the dark region near the center. Three days later, on the 27th of February the magnetic disturbance reached the earth. Due to bad weather no polar lights were seen, but the disturbancee was still strong enough on the 28 for producing polar lights.

For more information on coronal holes, see the following link, from which I have cited above:
https://www.swpc.noaa.gov/phenomena/coronal-holes

Magnetic activity

When I showed my images to Roger Spinnner and Jochen Richert they pointed out that they had recorded the magnetic field at their stations in Switzerland (http://www.ogvt.org/ and http://wetter.richert.ch). Below are the data for February 27 and 28 and for comparison March 18, which show the magnetic activity on a quiet day

start of magnetic activity 27 February 2019 at Bos-cha
magnetic activity 28 February 2019 increased activity 12:00 -21:00 UTC
magnetic activity at Montsevelier, Switzerland, 18 March 2019, a quiet day

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