Thursday, 9 February 2017

Observing diamond dust halos at the Bílá ski centre

Superparhelia and sharp light pillars
Taken by Daniel Neumann

At the night between 18th and 19th January 2017 me and my friend Daniel decided to try our luck and head towards the Bílá ski centre (approx. 50 km away). Before we headed out, we checked the webcams located at the centre. All cameras showed sharp and tall light pillars extending out of every light source. Faint superparhelia were visible, too.

The crystal swarm was extending 3 km away from the centre itself. On the way there, upcoming cars spawned tall light pillars and visible parhelia.

Just as we arrived, the centre closed down and turned off the lights. We parked near the slope and noticed that it was completely overcast. The crystals were in the form of very thick fog that was hanging in the valley. More on the "weather side" later.

As we walked for a few hundred meters away from the centre, we stumbled upon a very bright lamp illuminating a local church. Only a sharp and tall light pillar was visible. But as we stayed for a little longer, the whole situation changed and superparhelia started to appear. At first they were hardly noticeable, but with each minute they were getting brighter and brighter.

We decided to try our not-so-much bright "spotlight" to see if anything interesting appeared. And yes it did. By shining the lamp towards the snowy surface, true divergence took form and divergent sub-parhelia appeared. They were eerily 3D, hanging in the air. Along with them, an extremely bright and tall light pillar was observed, too.

A multitude of light pillars


Tall light pillars and superparhelia


Circumzenithal arc along with light pillar and superparhelia 


Light pillar, sub-parhelia, parhelia, and parhelic circle

Now let's discuss the weather situation a little. The temperature reached below -16°C which was lower than other temperatures observed at meteorological stations (due to the topography). The ski centre was at the time actually located at the edge of a low hanging stratus that was just barely touching the mountain ridge. The snow guns then probably nucleated its lower layer and the crystals started to precipitate out. Below is a georeferenced image from the Suomi-NPP satellite along with the location of the centre. The microphysical product along with a high resolution of the image shows how the edge of a low stratus (yellow colour) extends towards our location. Now bare in mind that this image was taken approx. 1 hour after we left, so the stratus actually retreated a little by that time. There are two "branches" of a low stratus visible at the image. The right branch follows the exact location of a local dam called Šance. The left branch follows a river called Čeladenka.

(c) Suomi-NPP 24h microphysical product

What stuns me about this location is its abundance of diamond dust occurrences. Almost every time the snow guns are operating, a crystal swarm is created within minutes and light pillars are always visible on the webcam images. I have a theory about why that happens:
  • Microclimate - the topography is in the form of a depressed valley, which allows for a cool and moist air to accumulate at the bottom. 
  • Moisture - the river that flows through the village could possibly be a substantial source of moisture 
  • Snow gun additives - if I have learned well, it is the additives in the snow guns that serve as nuclei on which the crystal formation takes place. In that case, they are probably using a specific additive that makes the crystal formation so abundant. 
The local relief of Bílá
Shaded relief + topographic map
(c) ČÚZK


METAR analysis shows a high pressure centre located above Czechia
(c) METAR

Temperature distribution

6 comments:

  1. Matej, Daniel, I think these observations not only contribute to halo science, but looking at the photos is a real aesthetic pleasure to the eyes.

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  2. One thing that always comes to my mind when reading about spotlight halos is how interesting it would be to build a mast for the lamp where you can lift and lower the source of light. I would really like to see a video where you can see how these 3D halos change shape when you move the lamp!

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    1. That's a great suggestion, Ágnes. My only worry that it would be an extra piece of kit needed to be carried into the field. It may be okay if there are two or more people collaborating but may become burdensome if you are a lone observer. Nevertheless, I think someone should give it a go and see whether it simplifies the spotlight workflow.

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  3. Stratus / fog turning into ice crystals probably accounts for much of the displays at Czech ski centers. Many photos I have seen show the sharp edge of the mother cloud at perimeter of the nucleated area. Ice turning clouds make the most violent displays and if diamond dust is formed almost every time at Bilá, then it is a paradise for halo man. Especially if there are easily accessible and open places without light pollution to do spotlight. Topography is also something good to have, so that you can have variation in lamp elevations. Bridges are excellent.

    I don't think the bacterial protein has much role in halo making. It may enhance the snow making process itself, but there will be amply ice particles for diamond dust formation even without additives.

    The horizontal patch of light in the photo where a guy is blocking the light is parhelia.

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    1. Interesting. Everytime the temperature is below freezing and there is a chance for diamond dust formation, I look at different cameras across Czechia to check if anything is happening. And almost everytime, Bílá is making halos while other places are totally dry.
      It is a paradise, but it has a few drawbacks. There isn't that much space to put the spotlight at, and then walk away say.. 100 meters. It is covered with buildings.. no bridges. But I have looked at the map and I have a few spots where I could experiment. Another problem is that due to the topography, the crystal cloud doesn't have much space to spread.

      Okay thank you, so it is probably due to its location and local microlimate only.

      Only parhelia, not a parhelic circle? Is it due to the close proximity of the lamp? Because I see that it is fairly bright up until the 22° mark and then there's almost nothing.

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  4. Good to have info about the way it is with Czech ski centers. Although nothing like the brutality at Bílá, Rovaniemi too has its share of diamond dust from low hanging clouds and fog (just last night there was a passable display). The season lasts long and no matter which direction or distance the stuff goes, there are plenty of places to spotlight. If something need to be complained of, it is that they have lifted the bar for starting the guns from -5 C to -10 C, which means the most impressive displays are missed.

    Those horizontal patches which end at 22 degrees are divergent parhelia. You would have seen the parhelic circle surround you near any outdoor light. From all I see, in spotlight beam your display would have been magnificent.

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