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

Making divergent subparhelia with a spotlight

By Jarmo Moilanen and Marko Riikonen

Here is divergent light subparhelia flanking the pillar. Spotlight displays are classical displays with little divergentness involved. A way to create truly divergent halos with spotlight is to point it to the ground. The reflection from snow then acts as a divergent light source. Another way that might work is to cover the lamp glass with a layer of snow. That would be a shorter lasting solution, though, as the heat of the lamp will melt the snow.

Most spotlight halos are visibly formed of separate crystal glitter. Not the divergent parhelia. They are solid objects floating majestetically in the air. One feels humbled before their lofty heights, just as a lesser subject might feel in the presence of royalty.

Below is another photo of divergent subparhelia taken some hours later. And also a little lunar display from the same night, which was the 18/19 January night in Rovaniemi.

Catching a divergent light halo effect predicted by simulations

Sometimes it is possible to make a deliberate attempt to photograph something predicted by simulations. On the night of 6/7 January we made such an attempt on the diffuse spots of light that in simulations are seen next to the divergent light subparhelion.

The effect is formed by a mixture of subparhelic circle raypaths, including 3157 raypath and sub-120° parhelion raypath. Its exact shape and position depends significantly on the crystal shape, like for the Liljequist parhelia.

To obtain an omnidirectional secondary light source that was bright enough we pointed the lamp directly to the snow surface. We took photos, looked at them more closely the next day, and there it was – those smudges of light predicted by simulations.

The photo above is actually from a slightly better case on the night of 18/19 January. Next to it is a simulation. Below is the one on the 6/7th.

Nicolas Lefaudeux / Marko Riikonen / Jarmo Moilanen / Marko Mikkilä