2010. március 29., hétfő

Bottlinger's rings!

At last they are here: good photographs of Bottlinger's rings! Tim Stone's images of Bottlinger's rings over Illinois were published today in Les Cowley's site ( 1 ). The rings lasted only for a few seconds, but luckily Stone was already taking photos of the subsun when the rings appeared, and the phenomenon became captured.

The original observation was made by C. F. Bottlinger during an air balloon flight on 13 March 1909 over Göttingen, Germany ( 2 ). The phenomenon lasted long, from 1 to 1½ hours. Bottlinger suggested that the ring could form from a reflection in crystals falling in pendulum motion. Computer simulations by Lynch et. al. in 1994 ( 3 ) showed, however, that this motion would produce uniform elliptical glow instead of defined ring. As an alternative they suggested plate crystals in gyration motion for the explanation.

Intuitively it would seem unlikely that all ice crystals in the cloud would fall exactly in the same inclination angle to produce Bottlinger's rings. Bottlinger's rings form in the same Altocumulus virga as elliptical halos around the sun, for which pyramidal crystals with very low apex angles has been suggested as an explanation by dutch S. W. Visser in 1960. These crystals would produce also Bottlinger's rings. The gyrating crystals could make elliptical halos by assuming that they are reflections of the Bottlinger's rings from horizontal plate crystals. This was suggested by Lynch et. al. Simulations by Sillanpää et. al. in 1999, however, showed that this can not model the observed elliptical halos, while pyramidal crystals yield much more satisfying results.

A photograph taken by Claudia Hinz ( 4 ) also clearly proves that elliptical halos are not reflections of Bottlinger's rings. These two halos have not been observed simultaneously, but an almost simultaneous observation was made by Leena Virta and I in 1999 in Resolute Bay, Canada. We observed Bottlinger's rings from an airplane that was flying under the Ac cloud layer and when the plane landed, the same cloud showed elliptical halos around the sun.

Tim Stone's photos show also fainter ring outside the main ring. Assuming the gyration explanation this would require two ice crystal populations with constant inclination angles. It will be interesting to try to simulate this with pyramidal crystal model. Les has already a simulation on his site, but he says the parameters could be fine tuned. The rings' dimensions and sun elevation are provided, so anybody can give it a try!

2010. március 19., péntek

Nomenclature woes

The kaleidoscope halos in a streetlight present some nomenclature problems. Please see the article Nomenclature Woes on my webpage (click the image above). I invite your suggestions for better names for the halos.

Walt Tape

2010. március 16., kedd

46° halo on snow surface

I welcome all fans of halo! Yesterday, March, 14th I observed halo in interesting enough combination. In this sunny day, walking on the Finnish gulf, I always checked the sky on presence halo. But it was not in the sky, but underfoot, on a snow surface. It was faintly painted, but clearly distinguishable arc. Having seen it, I have been surprised, after all the sun was at height nearby 20°. Only next day, we with the colleague (Vladimir Galynsky) have solved that it was 46° halo.

I continued supervision. Where I went on ice of the frozen gulf, halo followed ahead of me - is visible the big area has been covered by crystals. Soon in the sky has started to inflame 22° halo which has then reached enough big brightness. This all looked very unusual - small halo in the sky, and big on the earth.

Nikita Kulanov - Saint-Petersburg, Russia

2010. március 13., szombat

New halo simulation program, HaloPoint 2.0, released

In numerous entries of this blog there are halo simulations made with "a simulation software by Jukka Ruoskanen". The software has been under development for the past couple of years and has now reached the point where it is ready enough to be published. The software, HaloPoint 2.0, has its own webpage from which the software as well as it's user manual can be downloaded.

The software package is a zip-file. Simply extract it into a suitable directory and keep the two components of the software, HaloPoint.exe and Simulation.dll, always in same directory. The software runs in computers having Windows operating system (tested in XP and Vista). Also a .NET Framework 1.1 is required, which is already installed in most computers, but in case it is missing it can be downloaded for free from Microsoft pages.

In software homepage there are simulation examples together with parameter files so that getting started with the software is easy. In addition to the examples it is advisable to take a glance at the user manual so that the various features of HaloPoint 2.0 can be utilized.

Hope you'll have fun with it.