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View Full Version : hot to spot alpine subsuns



forestgnome
01-16-2009, 09:09 AM
http://www.spaceweather.com/swpod2009/11jan08/thomas-obrien4_strip.jpg


looking for a silver lining to this weather, I'd like to see/photograph an alpine subsun. Does anyone know more about this and more about how to spot one? What are the optimal conditions, temperature, what direction, what time of day, etc.?

Judging by the shadows and literature, they appear in the direction of the sun.

http://www.spaceweather.com/archive.php?month=01&day=11&year=2009&view=view

Thanks for any help

Bill O
01-16-2009, 09:19 AM
I've seen these skiing out west, CO and UT. Always on the first chairlift ride in the morning when the air is filled with ice crystals.

I'm not sure what is happening. On clear, cold mornings with no clouds in sight condensation will condense and precipitate out of the air.

Knapper
01-16-2009, 12:39 PM
I am trying to think of the last time I saw one out here and nothing immediately somes to mind. Growing up out west, I saw them a few times though. They appear directly below the sun at equal distance as the sun is high. They are most favorable a few hours after sunrise or before sunset and must be below your field of plane (ie, summits, chairlifts, etc) but if in a airplane, they can occur at any time of the day. They are formed by a reflection off small plate shaped ice crystals that are "falling" parrallel to each other to create a mirror like effect. The more parallel they are, the sharper the image. They are most commonly found in freezing fog, arctic cold (like the temperatures over the northeast right now) as the air is so cold, small ice crystals form, or in high, thin cirrus clouds. It is similar to the process that forms halos and sundogs.

Brad
01-16-2009, 12:57 PM
Here is a picture i took a while ago of a sun pillar.

http://images21.fotki.com/v832/photos/8/8235/3038430/IMG_3073a-vi.jpg

Charlie
01-16-2009, 01:48 PM
brad i saw something like that this morning .the sun was not showing yet but right where it was starting to come up there was this ray of light coming up off the top of the sun . then when the sun came up it was still there for for some time ,i wish i had a camera then
i will have one next time

Steve M
01-16-2009, 02:31 PM
Nice shot, Brad.

Brad
01-16-2009, 07:29 PM
I saw it - took the picture - but did not know what it was till later.

Bill O
01-16-2009, 08:41 PM
Here is a picture i took a while ago of a sun pillar.


Nice sun pillar, but not the same as a subsun...of the alpine variety.

JimS
01-17-2009, 10:48 AM
As Ryan stated, subsuns are reflections of the sun off of the top of plate crystals. Crystals tend to form in clear air under fair conditions in temps below zero, typically though you need to be below -10F to form them.

A good discription of the path of light can be found here:
http://www.atoptics.co.uk/halo/subsun.htm

How to spot them...well, they are rare...I've only seen them a few times on the summit. They are the same distance below the horizon as the sun is above, so an early or late sun is better...

Also of note, the crystals that form in extreme cold can do other neat things, like near halos, near sundogs, and light pillars from street lights. If you check out spaceweather.com today, there are examples of these displays, including one from whitefield, NH.

Here's my only subsun pic...
http://farm4.static.flickr.com/3122/3203208143_11572543c0.jpg

Brad
01-17-2009, 03:26 PM
Great picture and it helps us understand what it is.

KathyC
01-18-2009, 09:09 AM
I knew the answer all the time...:p

I know that at some point Forestgnome will get it and I can't wait to see it.