Sunshine has been a rare phenomenon in Finland this winter. On 16th January, the sky was finally clear and temperature had dropped to -25°C, so I headed to a nearby lakeshore to observe possible surface halos. There were indeed 22° and 46° halos visible on the snow, so I took a set of 335 photos by moving back and forth of a 50 m stretch of a road along the lake. The mirrored stack revealed that this was an odd radius display with 18°, 20°, 23° and 24° halos present. An interesting feature was that 22° and 23° halos were equally strong and well defined in the stack.
Two days later I got another chance to photograph surface halos in the same place. The temperature was -8°C. Only a modest 22° halo with some bright glints outside it were visible to naked eye, so I did not expect much from the stack. Nevertheless, I took 147 photos. This time the mirrored stack looked even better than two days ago: a strong 22° halo accompanied by several odd radius halos, including a clear 28° ring.
A comparison with the previous display (limited by blue frame in the photograph below) provided another surprise: the prominent ”22° halo” was in fact a 23° halo and 22° halo was missing. So this was an odd radius display with 18°, 20°, 23°, 24°, 28°, 35° and 46° halos. Although there are not many observations of 28° halo on surface yet, it seems probable that it is not as rare as has been thought. This gives some hope that a crystal sample can be obtained one day.
The strong 23° halo and the absence of 22° halo in this surface display is interesting. It means that the usual ”22° halo” on snow may in some rare instances be something else than it looks, but it is not easy to detect such cases from the abundance of common 22° halos. For example, the first observation of surface 28° halo on 7 April 2012 by Jari Luomanen and Marko Riikonen looks rather similar as the current one, and it may perhaps contain 23° halo instead of 22° halo (yellow frame below, photo Jari Luomanen). Although all photos in this collage were taken with Samyang 8 mm fisheye lens, the result should be viewed with caution due to the robust alignment.
If I still had lingering doubts on whether the 28° halos on snow surface were for real, this display have removed them for good. Of the other halos in the display, only the 23° halo is more clearly defined. Now we just have start taking those crystal samples, the potential for pay-off is huge. In Rovaniemi now the sun rises high enough for surface halos, but it won't help if it is constantly blocked by clouds.
ReplyDeleteCan't wait to see the crystal samples from such displays!
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