Parhelia

On the evening of 02-Jun-2014, I spotted a spectacular pair of parhelia (sun dogs) over the KAIRA LBA array. This is the first time I've seen two of them so bright and distinct -- normally one tends to dominate. Furthermore, the entire arc could be seen, including the enhanced region of brightness at the top.

Parhelia over the KAIRA LBA array. (Photo: D. McKay-Bukowski)

Parhelion over Pikku Malla

During the site inspection work, the weather was constantly shifting, with bands of cloud rolling across the skies. At one stage were were treated to some spectacular parhelia which pulsed and shimmered as the clouds and ice masked or enhanced the reflections. We took a lot of photographs, but none of them do justice to the scene... you simply cannot beat seeing it with your own eyes.

A parhelion and the sun over Pikku Malla.

Click on the "parhelion" label for this post to find others, along with an explanation of the parhelion effect.

Parhelion revisited

From rainbows to the aurora, our atmosphere is capable of generating some spectacular light effects. A few days ago, we posted a photograph of a parhelion. This is a light effect, caused by the scattering of sunlight from ice crystals in the atmosphere. Now, thanks to a recommendation from Jenny Shipway at the InTech Planetarium, we've found some interesting software that allows anyone to experiment with this phenomenon.

The recommended site was http://www.atoptics.co.uk/ — a site dedicated to atmospheric phenomena. The relevent section for what we saw from the KAIRA site is under 'Ice Halos'. Additionally, there is a link to some Windows software that anyone can download and use. And, that's what we've done here to re-create the effect that was seen at Kilpisjärvi.

The software does need some data. There was the time and date of the photograph (11-May-2011 16:48 UTC), from which we can use another online tool to get the solar elevation (as we didn't measure it at the time!). This gives a solar elevation of 16.9 degrees.

Below is the simulation (top image) and actual photograph (below it). As you can see from the comparison, it does a pretty good job of modelling what we actually saw.



Obviously there are a lot of lens flares within the photograph due to the limitations of the camera (both the lens and the CCD sensor therein) and I could have spent more time tweaking the camera angles to get the alignment correct. Still, it is a good match and indicates that the physics is well understood within the software.

The programme is pretty sophisticated and one can tweak parameters such as the ice crystal shapes and orientations to explore different effects.

Parhelion

During the recent site preparation and testing, the KAIRA team was treated to a spectacular parhelion. Parhelia (also known as "mock suns" or "sun dogs") are patches of light that appear 22 degrees to either side of the sun. The effect is caused by ice crystals in the upper atmosphere. The parhelion can be seen at the same altitude as the sun, near the right-hand edge of the image. Unfortunately, the photograph does not do it justice. The view is looking northwest from the LOFAR-FI609 HBA site.


Although in the image there are various 'lens flares' around the sun itself, the parhelion is a real atmospheric phenomenon, and is clearly visible to the naked eye. This is not the first time we've seen this effect over a LOFAR site. In fact, I photographed one from the LOFAR-UK site in Chilbolton last year (LINK).