Negative Solar Altitude Halos

[Alec Jones]

During a recent discussion, the puzzling topic of negative solar altitude halos came up. Given that these halos are theoretically possible, and with the exception of sun pillars, why are so very few or even no observations made or photographs taken of such phenomena? For example, does anyone have a photograph of a fragment of a 22 degree halo or an upper tangent arc after the sun has set? Obviously, a clear, unobstructed horizon is essential but can anyone offer an explanation of why such sightings are so rare?

Thank you in advance!

Kind Regards,

Alec

[Alec Jones]

Bump.

Anyone?

[Christian Fenn]

Peng!

[Claudia Hinz]

Hier sind auch welche dabei ...

http://www.meteoros.de/php/viewtopic.php?t=8101

[Nick Beck]

Those are some nice images Christian! The upper tangent arc is very sharp, the sun is obviously below the horizon. Do you know the exact location and time of the photo so it could be possible to calculate the sun height? I suggest it is around -2°.

[Alec Jones]

Hi Christian,

Thank you for replying and posting photos! In both your photos, how far below the horizon would you estimate the sun to be? Had it only just set? The second image is interesting as it also seems to show a faint pillar beneath the UTA. I wonder whether this is in some way making the UTA brighter than it would have been without the pillar?

Hi Claudia,

Thank you also for your reply. In part, it was this thread of yours that we were discussing which prompted me to post my question! However, there seemed to be some confusion as to the identification of the phenomena observed or at least the mechanism which caused it. At one point you were thinking possibly "mirage", no? This directly led us to discuss whether common phenomena such as fragments of the 22 degree halo, UTA's, CZA's etc would still be visible after the sun had set and how impressive they would look without the sun in the image.

So then, to refine my original question further, I would like to ask everyone, given the fact that there are very few extant photos of such phenomena, whether they think negative solar altitude halos are (a) frequent, (b)infrequent, (c)rare or (d)very rare. Would anyone like to hazard a guess as to how many such halos they have observed?

Thank you for further considering this question!

Best,

Alec

[Alec Jones]

Those are some nice images Christian! The upper tangent arc is very sharp, the sun is obviously below the horizon. Do you know the exact location and time of the photo so it could be possible to calculate the sun height? I suggest it is around -2°.

Hi Nick,

You beat me to it! I think you may be right with your estimate; the sun looks to have set very recently. I wonder whether photos exist showing a well defined UTA only a degree or two above the horizon? Now that would be something!

Regards,

Alec

[Kevin Boyle]

In reply to:

Hi Nick,

You beat me to it! I think you may be right with your estimate; the sun looks to have set very recently. I wonder whether photos exist showing a well defined UTA only a degree or two above the horizon? Now that would be something!

Regards,

Alec

Hello Alec,

Yes. I have seen a series of 22 degree halos around the moon a few days ago, occurring between 2100Z and 2200Z. The sun would have been around -30 degrees below the horizon so they're not as rare as you think!*

I have a couple of images of an upper tangent arc which persisted until slightly before true sunset. My west-northwest horizon is close to the astronomical horizon. This occurred on 8 August from 1930 UT to 1945 UT (CET+1) and the sun's altitude would have been at 1.8 degrees at 1930 UT to around half a degree above the horizon when it disappeared. There was a trace of a parry arc, and I have both parhelia reported for this period as well.

I'll work out how to send the pictures later.

Best,

Kevin

* - I'm joking and pulling your leg!!!

[Alec Jones]

Hi Kevin,

You know, I do believe I saw those very same halos as you the other day.

To be serious though, I'd love to see the photos you mention; I hope you will be able to post them at some point. I am not suggesting that such phenomena are rare once the sun has set, just that there seems to be few observations and even fewer photos of such events. I find this puzzling and I'd like to know why this is the case. So far, we have two photos of a UTA and one of a phenomenon which isn't properly understood. The very fact that this thread hasn't exactly been inundated with images shows there is a case to be answered.

I'll pm you at some point!

Best,

Alec

[Christian Fenn]

Picture one: 15.09.2007 19:48 MESZ, Height -3,0°
Picture two: 22.09.2009 19:30 MESZ, Height -2,5°

[Alec Jones]

Hi Christian,

Thank you for the information. Much appreciated!


Everyone,

We now seem to be getting somewhere with this puzzle, a start at least. Let's push things one step further. Does anyone have any photos of phenomena at an even greater negative solar altitude or is that asking the impossible? How about a UTA just skimming the horizon?!!

Regards,

Alec

[Nick Beck]

Hello Alec,

It would be impossible to see the upper tangent arc skimming the horizon. The sun would have to be -22° in elevation, and it would be completely dark then, cirrus clouds would have long been in the dark. The sun elevation when cirrus clouds begin to go dark is only a few degrees unfortunately.

Regards,

Nick

[Alec Jones]

Hi Nick,

Good point! Why didn't I think about that?!!

Regards,

Alec

[Michael Ellestad]

Hey Guys,

Speaking of upper tangent arcs after sunset, back in 2008 on October 13th there was a huge halo complex showing very nice column arcs well after sunset I got a very nice upper tangent arc and this thing was not only bright but very sharply defined and red. Theres a pic of it in the halo reports blog somewhere.


Regards,

Michael

[Nick Beck]

Hello Michael,

I found the display in the Ice Crystal Halos blog, and it certainly was one spectacular display! The moon halos were just awesome! It mentioned the low sun tangent arc, but there weren't any pictures on there of it. Maybe you could find it? It'd be nice to see!

Regards,

Nick

[Alec Jones]

Hi Michael,

I hope you will be able to find the photo of the UTA if you can spare the time. Do you remember whether the UTA was very strongly sunvex and any altitude information? Was it similar in shape to the ones posted by Christian above?

Thanks!

Alec

[Michael Ellestad]

Hey Alec,

Yeah you are right its not on there after checking a moment ago and I don't know why it did not get posted I guess I forgot to have it posted. I need to make me a blogger blog as well too for atoptics.

Regards,

Michael

[Alec Jones]

Hi Michael,

With all your fantastic observations you definitely need an online presence!

Back to the UTA, do you think you still might have the photo in question? I would love to see it!

Regards,

Alec

[Michael Ellestad]

Hey Alec

Yes I got pics of it but they along with the entire display are on my 1 terabyte external drive. Like I said I need to make me a blogger halo and atoptics blog for all the halos and optical effects I see in Ohio.

BTW: I now have a blog made and now how to post my images to the AKM forum I wish I could upload the images but it does not work that way.

Regards.

Michael

[Alec Jones]

Hi Michael,

Don't worry about the photo, I'm exactly the same. I have thousands of photos but I can't always find the one that I want straight away. Really frustrating at times!

Your new blog sounds interesting. What is it called? Could you post a link to it as I'm sure a lot of people would be interested. Thanks!

Best,

Alec