The owner's trip to Tromsø: 11 to 14 March 2022
The author's own experience, from his diary of the trip. Next to it: what the model says about the same nights. The model matched two of the three nights.
The trip to Tromsø night by night
- 11 March. Flew to Tromsø. The sky was cloudy and no aurora was seen. The forecast he had read said 100% cloud.
- 12 March. Sunny day in town. The minibus tour in the evening, with a faint start to the aurora and then a strong, moving display.
- 13 March. Cable car to the top. Hiked over three peaks (he recorded 776 m of climbing). From the top he saw a faint, reddish aurora until about 21:00, when he went down because of the cold.
- 14 March. Early bus to the airport.
The owner's experience: on 12 March 2022 he joined a minibus tour run by Chasing Northern Lights. The pick-up was at 18:00. About 12 people were collected from several hotels. The driver came from West Pomerania and the guide from southern Sweden. The organiser supplied the tripods. The guide served hot chocolate and cookies, and cleared a snow circle for a fire. The group stayed until about 00:30 to 01:00. The aurora was very active on the drive back. The owner's notes from 2022 are his own.
The model says the night of 12 March was a good night in the grid cell, and the night of 13 March was a cloudy one. The owner's notes and the model disagree about 13 March.
What did the model show in Tromsø on 12 and 13 March 2022?
Show as table
| Local time | Kp | Cloud at Tromsø (%) | Sun altitude (degrees) | Model |
|---|---|---|---|---|
| Sat 12 Mar 16:00 | 0.3 | 28 | 6.5 | not dark |
| Sat 12 Mar 17:00 | 0.3 | 66 | 1.7 | not dark |
| Sat 12 Mar 18:00 | 0.3 | 76 | -3.5 | not dark |
| Sat 12 Mar 19:00 | 1.0 | 88 | -8.6 | not dark |
| Sat 12 Mar 20:00 | 1.0 | 70 | -13.4 | dark |
| Sat 12 Mar 21:00 | 1.0 | 47 | -17.6 | dark |
| Sat 12 Mar 22:00 | 1.3 | 19 | -20.8 | good |
| Sat 12 Mar 23:00 | 1.3 | 17 | -22.8 | good |
| Sun 13 Mar 00:00 | 1.3 | 11 | -23.4 | good |
| Sun 13 Mar 01:00 | 1.3 | 32 | -22.5 | good |
| Sun 13 Mar 02:00 | 1.3 | 76 | -20.2 | dark |
| Sun 13 Mar 03:00 | 1.3 | 87 | -16.7 | dark |
| Sun 13 Mar 04:00 | 0.7 | 95 | -12.4 | dark |
| Sun 13 Mar 05:00 | 0.7 | 84 | -7.4 | not dark |
| Sun 13 Mar 06:00 | 0.7 | 51 | -2.2 | not dark |
| Sun 13 Mar 07:00 | 0.3 | 24 | 2.9 | not dark |
| Sun 13 Mar 08:00 | 0.3 | 48 | 7.7 | not dark |
| Sun 13 Mar 09:00 | 0.3 | 71 | 11.8 | not dark |
| Sun 13 Mar 10:00 | 4.0 | 86 | 15.0 | not dark |
| Sun 13 Mar 11:00 | 4.0 | 94 | 16.9 | not dark |
| Sun 13 Mar 12:00 | 4.0 | 96 | 17.5 | not dark |
| Sun 13 Mar 13:00 | 5.7 | 83 | 16.7 | not dark |
| Sun 13 Mar 14:00 | 5.7 | 26 | 14.5 | not dark |
| Sun 13 Mar 15:00 | 5.7 | 6 | 11.1 | not dark |
| Sun 13 Mar 16:00 | 5.3 | 27 | 6.9 | not dark |
| Sun 13 Mar 17:00 | 5.3 | 36 | 2.0 | not dark |
| Sun 13 Mar 18:00 | 5.3 | 40 | -3.1 | not dark |
| Sun 13 Mar 19:00 | 5.7 | 75 | -8.3 | not dark |
| Sun 13 Mar 20:00 | 5.7 | 94 | -13.1 | dark |
| Sun 13 Mar 21:00 | 5.7 | 97 | -17.2 | dark |
| Sun 13 Mar 22:00 | 6.3 | 98 | -20.5 | dark |
| Sun 13 Mar 23:00 | 6.3 | 98 | -22.4 | dark |
| Mon 14 Mar 00:00 | 6.3 | 99 | -23.0 | dark |
| Mon 14 Mar 01:00 | 5.7 | 98 | -22.1 | dark |
| Mon 14 Mar 02:00 | 5.7 | 100 | -19.8 | dark |
The same replay on a zoomable map (MapLibre, with OpenFreeMap tiles). It loads only when you click.
Technical details: page weight
Variant A, above: the base map is drawn into the page (15 KB). The player and this night's data load next to the map (25 KB).
Variant B loads after the click: 731 KB in total, of which MapLibre GL JS is 253 KB. The rest is map tiles, style, fonts and this night's data.
On 12 March the sky over Tromsø turned dark at 20:00 and cleared at 22:00. Cloud stayed at or below 40% until 01:00, lowest at 11% at 00:00. Kp was 1.0 at nightfall and 1.3 in the good hours. That is quiet by the global standard. At that hour Tromsø sat inside the estimated oval, 94 km poleward of its southern edge.
The next evening was the opposite. Kp rose to 6.3, a geomagnetic storm (G2 on the NOAA scale). But cloud reached 75% at 19:00 and 94% at 20:00, the first hour dark enough to count. The model calls that night cloudy.
Did the model match the trip to Tromsø?
The model matched two of three nights. The author was in Tromsø from 11 to 14 March 2022. Here are his notes next to the model, night by night (cloud and Kp over the dark hours):
| Night | The author's notes | Model | Dark hours | Lowest cloud | Highest Kp | Agrees |
|---|---|---|---|---|---|---|
| Fri 11 March | Rain and full cloud; no aurora. | cloud | 9 | 100% | 4.7 | yes |
| Sat 12 March | Strong, fast-moving aurora on a minibus tour about 50 minutes from Tromsø. | seen | 9 | 11% | 1.3 | yes |
| Sun 13 March | Faint, reddish aurora from the upper cable-car station until about 21:00, then cloud. | cloud | 8 | 94% | 6.3 | no |
The 12 March match is partly built in. The activity bar of 1.0 was set from that very night, so it is not a fair test. 11 March is a fair test, and it passes: the grid cell was 100% cloud in all 9 dark hours.
13 March is a miss. The author watched a faint, reddish aurora until about 21:00. ERA5 shows 94 to 97% cloud over the grid cell at that time. Between 16:00 and 18:00 cloud was 27 to 40%, but the sun was still less than 12 degrees below the horizon, so the model does not count those hours. Either the clouds had gaps finer than the model's 31 km grid, or they reached the cable car later than the model shows. We left the thresholds as they are.
The moon was 74% lit on the evening of 12 March and 83% on 13 March. It was getting fuller.