By Lasse Nurminen and Marko Riikonen
The cold spell that started in February in Finland brought along some surface helic arc displays. In this post we represent our observations. The past surface helic arcs have been largely symmetrical, but this time asymmetrical displays dominated.
Finally some decent winter weather arrived even to the southwestern parts of our country. Lots of snow and the temperatures around -15°C for a long period. In the coldest mornings the temperature dropped to as low as -25°C. It took some getting used to it, as during last winter the temperatures here were stuck mostly around 0°C.
So because of the nice winter I´ve been keeping my eyes open for the possible halos on the ground also. I only observed a few faint 22° rings until this case.
One day the surface of the snow draw my attention as it looked pretty rough. The ice crystals were pointing upwards, usually the surface looks much smoother. It took me a couple of days to wake up my slow brain cells. I remembered seeing some rare halos spotted from a surface looking pretty much the same. A little search from Taivaanvahti website confirmed my thoughts. So the ”hunt” for the surface helic arc was on.
These type of crystals need open space, clear skies and wind to form. I could already tick all of those boxes and I began to search for the possible arcs from a few small landfill hills on 4th of February. There wasn´t too large uniform areas on the slopes to be found, but still I found one spot with the arcs visible to the naked eye. Nothing too fancy though, so I decided to shoot a few photos to stack them in the post processing. The stacked photos helped to identify the arcs even better.
During the last case I intended to photograph some crystals a little closer as well. I thought that I had my set of extension tubes in my backpack, but for my disappointment they weren´t there. The next day I had them along, but the situation on the ground had changed. No more arc(s), but the crystals still had the same shape for most parts. This blade like growth in the top part makes the crystal look a little like fish scales with the growth rings to me, too angular though.
While the southern part of the country was already enjoying surface helic arcs, otherwise good prospects up north in Rovaniemi were at the same time spoiled by light nightly snowfalls. But then the night between 7 and 8 February was all clear and next day surface helic arc, which other arm was brighter than the other, was visible on river Kemijoki.
The helic arcs by Antti Hämäläinen and Maria Tirkkonen were serendipitous finds. Petri Martikainen spotted these from scenic shots published elsewhere and encouraged the photographers to leave observation in Taivaanvahti.