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Ursa Astronomical Association

Quiet aurora band - 27.9.2019 at 22.32 Juupajoki Observation number 85854

Visibility II / V

Riku Talvio, Ursa (Länsi-Suomi)

The weather forecast peaked on a cloudy night, and that’s what it looked like at first; my first mooring place was firmly in the cloud. However, in the direction of the north, a promising small opening was visible, so I decided to go and see if there would be a suitable place to use it - and it was there. The sky was clear, except for one cloud raft that covered almost all the green that was on the northern horizon. I waited a long time without seeing the northern lights, and I didn’t even bother to set up the camera equipment. Then a "torch" began to rise from the west / northwest, the development of which I admired, completely forgetting to take pictures. Eventually I realized digging into the camera backpack, and got a picture of the already fading STEVE.

More similar observations
Additional information
  • Aurora brightness
    • Dim auroras
  • Observed aurora forms
    • STEVE-arc info

      STEVE (Strong Thermal Emission Velocity Enhancement) is an aurora-like phenomenon that can be observed in middle latitudes. STEVE does not belong to traditional auroras as a phenomenon, but may appear at the same time with them.

      STEVE looks like a narrow, white or mauve arc that is clearly separate from the rest of the aurora oval in the pole-ward side of the sky. In Northern Europe, STEVE can sometimes be seen quite far from the oval and be visible across the southern half of the sky.

      STEVE, Keijo Lehtimäki
      A mauve STEVE with a clear gap to the oval. Image: Keijo Lehtimäki

      It forms a long and narrow east-west aligned dim line that goes across the night sky. The length of the arc can be over 2 000 km and it is located at altitudes of 110-300 kilometers.

      The best time for observing STEVE is when the active aurora of a substrom have subsided.

      The arc is white, grey or light purple in color, but the appearance of the arc may vary slightly. In more colorful versions, the bottom edge of the arc shows while/grey color, whereas the upper part has more purple shade. These colorful versions are called Double-Layer STEVE.

      Double layer STEVE, Eero Karvinen
      Double-Layer STEVE. Image: Eero Karvinen

      STEVE's appearance can resemble single, detached rays or there can be rays within the arc itself.

      Riku Talvio, STEVE
      A ray-like STEVE. Photo by: Riku Talvio

      Quite often purple rays within the aurora oval itself get mistakenly identified as STEVE. While within the aurora oval the purple rays tend to disappear relatively fast, STEVE-events can last from ten minutes to hours.

      STEVE very rarely shows green color, whereas lower edges oval's traveling rays tend to be clearly green. However, occasionally there may also be a green, "toothed" band called ”picket fence” below and aligned with the STEVE arc.

      Sirpa Pursiainen, STEVE picket fence
      STEVE with picket fence. Image: Sirpa Pursiainen

      SAR arcs are a different phenomenon happening in the same region that sometimes gets mixed up with STEVE. SAR-arcs, however, are more diffuse, dimmer or fainter, purely red, and lasts longer than STEVE, even days.

      Atacan Ergin, STEVE SAR
      This rare image shows a red SAR-arc with a white STEVE arc. There is an area without aurora light around STEVE. Image: Atacan Ergin

      When photographing a suspected STEVE, it is important to try capturing both the arc form and the arc's location in relation to the rest of the oval.

      In some cases, fine westward-moving structures can be observed within the arc. These can be captured by taking videos of the event or capturing short-exposure animations.

Comments: 3 pcs
Mikko Peussa - 28.9.2019 at 14.51 Report this

Hieno kuva tuosta ilmiöstä!

Timo Alanko - 3.10.2019 at 20.17 Report this

Onhan tuo upea ilmestys! Tiedetäänpä, mitä seuraavien reposten aikana tähyillään. Tuskin tulee tavaksi. Moni sai tuosta once in a lifetime - otokset :) 

Eero Karvinen - 4.10.2019 at 00.53 Report this

Villi arvaus on, että näitä tullaan näkemään lisää. Nyt sai arvokasta dataa magnetometristä, millaisessa olosuhteessa esiintyy. Hyvin osui yhteen kirjallisuudessa mainittuun olosuhteeseen, eli alimyrskyn palautumisvaihe ja ennen magneettista keskiyötä.

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