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Jun Lao: "Halos in the sky" (Oct 2, 12:37):
> Hello!
>
> The list is very quiet. I don't know if I have been unsubscribed but
> certainly I haven't received anything for a long time.
It's been quiet.
>
> My job requires me to go traveling by air quite a few times a year, and
I
> always try to make it a point to get a window seat during daytime trips.
I
> always enjoy looking out to spot halos and sundogs while in the air.
Any
> reason why halos seem to be more prominent when one is airborne? The
inner
> dark region seems to be much darker when seen higher up.
Well, at least the lower clouds won't prevent you from seeing the halos,
which is
the case at the ground quite too often. Can't think of any other reason
for now,
unless the lower background brightness of much thinner atmosphere up there
counts.
>
> Another thing I noticed while flying a few weeks back when the sun
wasn't
> still so high in the sky (about 9:00 a.m. local time), was that the top
of
> some cumulus clouds had some thin wisps that were colored with the
colors of
> the rainbow. These clouds were opposite the sun's position in the sky.
It
> was quite nice seeing such dainty clouds having such colors. The thin
wispy
> clouds above the cumulus clouds showed these colors, but not the puffy
> cumulus clouds beneath or else scattered around.
>
You probably saw a glory. It is quite common phenomenom for airborne
observers,
but rare at the ground, except in some special locations, such as at
mountains.
The glory is much like the difraction rings around the sun and it is
centered at
the anti-solar point, that is, around your shadow. If the plane is near
enough
the clouds, you can actually see the swadow of the plane at the center.
The
glory can only be seen in water clouds or in a fog (water droplets),
because the
ice crystals can't have the electromagnetic surface waves necessary for
right
kind of backscattering.
> Anybody else notice these things when airborne?
The glory can be seen almost any time when there are clouds at the
anti-solar
point, can't say much about the statistics of halos - I don't fly that
much.
>
Yours,
Timo Nousiainen
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