|
meteoptic-l [ät] ursa.fi
message archive
This is meteoptic-l [ät] ursa.fi message archive.
Note, your can reply the messages on this page only if your
are already subscribed the list.
» To the end of the list/message
- PARABOLIC ILLUSION
>From Paul Williams:
> Looking towards the sun, one could see a parabolic arc
> openning towards the sun in the frost on the ground. This arc
> was coloured red to violet from the inside out. I believe the
> horizontal arc was a 22o halo normally seen as circular around
> the sun in the air. This halo was the conic section of the
> horizontal ground intersecting the cone of vision around the
> sun. The sun elevation at the time was approximately <10o.
> There were no ice crystals or fog in the air, thus no "normal"
> halo effects.
Thank you Paul of the interesting frost 22-degree halo experiences.
The parabolic shape is an illusion. A good picture of similar 22-'
degree halo is included in Tape's book "Atmospheric Halos" (AGU
Antarctic Research Series,1994).
2. DEBATE OF BOTTLINGER'S
>From Les Cowley:
>> I do not understand the appearance of Bottlinger's rings - would
>> someone care to give a description?
Your question hits directly to the biggest current debate on halos.
These two phenomena seem very similar: 1. elliptical halos that
appear surrounding the sun and moon themselves (see: Hakumaki and
Pekkola, "Rare vertically elliptical halos", Weather (UK), December
1989). 2. Bottlinger's rings that appear around the subsun (or the
"submoon"). Yet no-one knows for certain how these things are caused -
this is mainly due to the total of lack of crystal samples.
There is two competing explanations. The papers that Trankle refers
(quoted below) are in favor of multiple scattering hypothesis, which was
suggested first by Bottlinger himself in the beginning of this century.
Sofar no halo has been convincingly shown to arise in multiple
scattering. It is very much possible this will some day happen.
Another choice is single scattering from such crystals that would have
pyramidal surfaces suitable for building these small elliptical rings.
One alternative representing choices of second hypothesis was discussed
shortly by Visser in mid 20th century.
The occasionally recorded color in elliptical halos, a recent
polarisation observation by Sillanpaa and the observed brightnesses of
elliptical halos and Bottlinger rings tend to favor single scattering.
Regards, Marko
>From Eberhard Trankle:
>It is not easy to explain Bottlinger's rings.
>Two papers on Bottlinger's rings were published recently
>
>D.K.Lynch, S.D. Gedzelman, and A.B. Fraser,"Subsuns, Bottlinger's
>rings,and elliptical halos,"Appl.Opt.33,4580-4589(1994)
>E. Trankle and M. Riikonen,"Elliptical halos, Bottlinger's rings, and
>the ice-plate snow-star transition,"Appl.Opt.35,4871-4878(1996)
|