A sub-zero rainbow!

There’s a rainbow across Lake Monona this morning. The temp is -6. We’re guessing it’s from steam rising from the lake. It’s been so mild this winter up to this point that the lakes haven’t frozen. I wish I could post a decent pic, but my crappy phone cam doesn’t do it justice.

“steam” – actually, condensation from the steam, since steam itself isn’t really visible – tends to be in really small droplets – sub-micron ones, that’s don’t make rainbows with color separation. It makes fogbows, which are white:

I suspect that there must be larger droplets suspended in the atmosphere that caused a classic colored rainbow. Even though ground temperatures may be sub-zero, it;'s possible for temperatures higher up to be somewhat higher.

Interesting – in this case the bow is only visible near ground level up to … can’t really tell. but you see the two end of the bow going up maybe a few hundred feet, and the rest is unseen. Maybe the middle doesn’t exist because the conditions are only right at the ends, or lower down?

Bingo. One frequently gets only partial rainbows (and often partial ice crystal haloes, too)

Another thought occurs to me – fogbanks are terrible at making color-separated rainbows, but they’re the perfect medium for glories. You normally don’t see a glory at ground level, because they’re at the anti-solar point. You see them from mountain tops looking down into valleys, or from airplanes looking down into clouds. The glory forms a tight circle around your shadow.

I could see it possible that you’re seeing a glory at sunrise, if you’re looking slightly downward into the fogbank atop the lake.

was it a glory you saw?


No there is no fogbank atop the lake. It’s a clear day. But I am looking downward – not very far, from 6 floors up.

There needn’t be an opaque fogbank. You said that you were seeing the effect in what you thought was steam above the lake. The fact that you’re looking down into it would tend to support the “glory” hypothesis.
You can tell them apart this way - the rainbow is MUCH larger in angular extent than a glory. The rainbow extends about 42 degrees in radius from the anti-solar point (so it extends across about 84 degrees total). The Glory is much smaller, and tightly concentrated around the antisolar point. (It has no definite extent, and may go through more than one spectral order, as you can see in the pictures I link to)
If there are colors close to the shadow or center, it’s a glory. If the only color is in the 42 degree band, it’s a rainbow.

They’re not very good, but here are pictures of the two ends.

Links were broken for me.

Requires a login to see the damn things.

Fuckin’ Google. According to them anyone with a link to the album can see it, signed in or not. I assume that meant the individual pics within the album too.

Can you see the album? There’s only a few pics and the others are my new car. The rainbow pics should be pretty obvious.

That worked. And, nice car. :slight_smile:

Aha! I can see the pictures.

What you have there isn’t a Rainbow or a glory. It’s a pair of Sondogs, AKa Parhelia, along with a portion of the 22 degree halo

The effect is due to light refracted by ice crystals, not water drops, so it’s not surprising if you see it at below-zero temperatures (although what I said earlier about ground temperature and high altitude temperature possibly being different still holds – sundogs have been seen in the desert)

Sundogs proper are due to oriented hexagonal (and trigonal) ice plates – they are oriented by the aerodynamics of falling bodies with their hexagonal axis horizontal. This keeps the bright spot to a spot 22 degrees to either side of the sun (about half the size of a rainbow, but much bigger than a glory). If there’s a bit of turbulence, the bright portion broadens into a stripe (actually a portion of the 22 degree halo circle), and if there’s a lot of turbulence you get a complete halo at 22 degrees.
Sundogs are actually incredibly common – I restimate them to be about 10 times as common as rainbows, and I find that other people’s estimates agree with mine. It’s just that people don’t notiuce them unless they’re pretty impressive or spectacular. Sundogs can appear simply as light patches in the sky, or they can be huge multicolored swtaches.

Their colors, by the way, are the opposite of rainbows – red closer in toward the sun, blue on the outside. Rainbows are red away from the antisolar point.

Plus, sundogs are centered on the sun – rainbows and glories are centered on the antisolar pooint. Thatr alone should make it clear that this isn’t a rainboiw – rainbows are on the opposite side of the sky from the sun.


Thank you. That’s gotta be it.

I once, as a child, saw what in retrospect must have been a sundog, that appeared at the time to be “another sun”. I’m sure it wasn’t as bright as the real Sun, but I have only my childhood memories to go by.

There was also a rare occurrence of lake effect snow this morning on the other side of the isthmus (over Lake Mendota).

A day for oddball local weather phenomena!

Except that, technically, sundogs aren’t really all that rare – it’s just that most people aren’t aware of them (especially the non-spectacular kind), even when they’re pointed out to them.

I used to point them out to people, to the chagrin of Pepper Mill.

Here’s a fogbow ref at a good site: http://www.atoptics.co.uk/droplets/fogbow.htm.

The also have a picture of the day that’s updated about 3x/week. It’s always something interesting & pretty. That’s at http://www.atoptics.co.uk/opod.htm. They always have good explanations of how the optics work to produce the effects.

I’m very familiar with that site. Here’s their page on sundogs: