|
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
- Forwarded message from "L-Soft list server at Finnish University and
Date: Thu, 13 Jan 2000 13:27:38 +0100 (MET)
From: Paul Schlyter <pausch_at_saaf.se>
Subject: Re: Rainbow
> Quoting Mark Vornhusen <mark.vornhusen_at_T-ONLINE.DE>:
>
>> I think it is possible that also halos can be caused by reflected
>> sunlight. E.g. halos in ice-fog above a frozen lake. Probably also
>> secondary halos to the subsun do exist. What do you think?
>
> I am just thinking that the ice cover on the lake is maybe not so
> good reflector as a water surface. There are almost always some
> impurities in the ice, maybe some air bubles in it orsome snow on it
> and the ice surface is not so even as a calm water surface. The
> light will diffract too much.
This is true for most ices, but when the ice is just fresh, its
surface may indeed be very smooth. Such an ice - if thick enough -
is the best ice to go skating on btw. Usually such ices only appear
on freshly frozen lackes: after only one or two weeks, that smooth
ice surface may be gone.
> In case of winter and diamond dust in the air may be so close enough
> the reflecting surface the reflected halo effect is possible. You
> know in case of rainbows the water droplets are, I think, quite near
> the water surface. In summer conditions I don't think, the reflected
> halos are possible, because the ice crystals are in so far away from
> the reflecting surface.
In January 1997 there was a splendid halo display over Stockholm,
caused by ice rystals very low in the air. This is the best halo
display I've ever seen, and it's the only time I've seen an
uninterrupted 45-degree halo (or at least the part above the horizon
as uninterrupted). Many other halo components were visible as well:
vertical pillar, horizontal arc, circumscribed halo, and even
anti-helion arcs (near the horizontal arc but opposite the Sun). I
watched this from a balcony at the 7th floor, and parts of the
22-degree halo even appeared IN FRONT OF THE NEXT HOUSE, some 100
meters away! The entire 22-degree halo could be seen, even though
the Sun only was some 10 degrees above the horizon!!!
- End forwarded message -----
|