Originally posted by Raulken
Since I am not familiar with sundog phenomena, is this a normal presentation?
Welcome to ATS Raulken.
How do you define "normal"?
Just to be clear,
sundogs (or "parhelia") are one particular sub-type of ice halo. In the image/footage, what we are seeing (sundogs, parhelic
circle, tangent arc, parry arc, etc ) are all collectively known as a "display of ice halos and arcs".
A display like the one we are seeing in the images/footage would be classed as "complex display", and whilst complex displays are not very common at
all, they are "normal".
To elaborate a bit, ice halos/arcs are caused when sun light shines trough ice crystals that usually form high altitude clouds. For a specific halo to
be formed, those crystals have to be a certain shape. It's not often, but sometimes the conditions are right for less frequently seen shapes to form,
which in turn gives rise to less frequently seen halos/arcs.
In some cases particular halos/arcs are seen because the ice crystals are more uniformin shape or well orientated, so light that is normally not
strong enough to be visible, is now visible, resulting in multiple sub-types of halo being produced by the same shape of crystal.
In a complex display, the conditions had to have been right for a few different less common crystal shapes to form (or for more
uniformity/orientation), each giving rise to particular halos/arcs.
In this case it seems that Sandy might have something to do with those particular conditions being present, although more usually complex displays are
not associated with extreme weather events from what I have seen.
Originally posted by Raulken
Did anybody also notice the same small light concentration not quite opposite the sun along the circular path at 5:26 and 4:26?
Yes - it's actually a
120° parhelion (or "sundog"), which is caused by the same plate shaped
ice crystals that cause the more commonly seen 22° parhelion/sundog.
It's an easy one to identify since parhelia can always be found on the
parhelic circle (the
"circular path" which you referred to which is very bright and obvious in the display we are discussing here), and 120° parhelia are always found on
the opposite side of the sky from the Sun.
They might be easy to identify in a case like this, but they are not always so easy to spot...
Always look carefully for 120° parhelia whenever the ordinary 22° sundogs are very bright. They are not particularly rare, but when they are
diffuse they can sometimes be difficult to distinguish from bright areas of cloud.
The parhelia result from at least two internal reflections. Rays enter the plate crystal top face, internally reflect off two adjacent side faces then
leave through the lower face. The horizontal deflection of the ray is always 120° regardless of the angle of incidence of the incoming ray ~ hence
the parhelion rather than yet another parhelic circle ray.
These things can also be hard to see unless there is a uniform layer of cloud/ice crystals all over the sky, which is not usually the case. More
usually there are small patches of the "right stuff", and as those patches drift across the sky, when they reach the right position in relation to the
sun in the sky, they "catch" as I like to call it.
For example, here's the most recent 22° sundog that I photographed just over a month ago. It's actually a "contrail dog" - contrails are also made of
ice crystals. This particular one was only visible for perhaps a minute or two as it drifted over the right part of the sky for a sundog to be
visible. You can see the difference in light intensity in the parts of the contrail that are "catching" (on the right) compared to the part that is
not "catching"(on the left). The Sun is just out of frame on the right, and roughly level with the dog.
Wide angle view:
Telephoto:
Here are some more sundogs that I photographed for comparison. Note the similarities in colours (more red closer to the Sun) that are characteristic
of 22° sundogs.
Partially obscured sun dog.
We do get quite a lot of low altitude cloud that tends to obscure the high altitude clouds that produce halo/arc displays here in the UK, but even so
we see
frequent halos/arcs like this circumzenithal arc (CZA) very frequently:
We also see the occasional rarer halo, but so far most have eluded our DSLRs!
Originally posted by Raulken
Since the videos are from two different locations, maybe it can be ruled an actual object? Just speculating.
It's not unheard of for the same display to be seen from multiple locations as the ice crystals/clouds drift or are pushed (by Sandy in this case)
over different areas. It was mentioned in the spaceweather.com article that the displays were all observed on the edge of Sandy, and the edge of Sandy
tracked/extended over quite a few states, so it's not surprising that these relatively rare displays were seen in a few places.
edit on 6-11-2012 by FireballStorm because: ran out of room
edit on 6-11-2012 by FireballStorm because:
clarification
edit on 6-11-2012 by FireballStorm because: fixed typos
edit on 6-11-2012 by FireballStorm because:
clarification