What meteorological phenomenon was this?

Flying from Italy to the Netherlands this last weekend I noticed a strange meteorological phenomenon as we crossed the Alps. I was on the right hand side of the plane, in the window seat. The sun was on the left of the plane. Looking down to my right, I could clearly see projected on to the clouds a circular rainbow type image kind of like a sundog (but not around the sun, obviously).

The air in the alps is extremely cold at the moment, with plenty of snow down. Presumably there’s lots of ice crystals in the clouds, which caused whatever it that I saw. However, meteorologists and associated experts have names for just about phenomenon you can care to imagine, so I was wondering what precisely the term is for what I saw. Does anybody know?

Sounds like you saw an ordinary rainbow to me. You don’t have to be on the ground to see them, obviously. If you were on the ground I’d say you saw a sundog since those are just refracted light through airborne ice crystals.

Sounds like a Glory:
http://www.atoptics.co.uk/droplets/glorair.htm
http://www.atoptics.co.uk/droplets/glory.htm

Related to:
Heiligenschein, but on clouds
Opposition effect

It does sound like a Glory.

A Glory is a rainbow-like series of colored bands surrounding the shadow of the plane, seen on the clouds. It’s very commonly seen on airplanes, and I always look for them. Before airplanes, about the only way you could see a glory was to be on a mountain top looking down into a valley filled with mist. You would see the glory as a halo around your own head (If you were with companions, you would only see the glory around your own head (and each companion would see the glory around their own heads), something which could give you a messiah complex.

Yep, it looked almost exactly like that first picture of a glory. That was quick. Thanks.

Similar to Brocken spectre. Same mechanism pretty much.

Have seen both numerous times. Neat.

Closely related prior thread: http://boards.straightdope.com/sdmb/showthread.php?t=288703

I have an even weirder one. Twice I flew to Europe near the summer solstice, and both times I was seated on the left of the plane as it took the Great Circle route up over Greenland and other points north. Despite the fact that the sun was down, I could see twilight in the far north all the way there, AND a nighttime rainbow! It was about 20 degrees below the horizon, looking straight north towards the putative location of the sun.

You don’t see a rainbow along the direction of the sun – it’s centered on the antisolar point, the point in the sky opposite the sun. Also, it doesn’t make sense that you can see a rainbow when the sun itself is below the horizon.
It seems likely to me that you saw either a portion of an ice crystal halo, or one of the upper tangent arcs – those are along the direction of the sun. They surround the sun, and they show color separation as a rainbow does.

Are you sure those phenomena weren’t the Aurora Borealis?

While glorys may exist in cold conditions like those found at airline cruising altitudes or from a mountaintop, that’s not a requirement is it? I’m pretty sure we used to see them from our helicopter on the often foggy North Slope during the summer. Altitudes were probably less than 2000 feet and temps in the 70s or so.

Glories are formed by water droplets, like rainbows (and unlike most haloes), so you actually want to be in a warmer location to see them – you won’t see them if the conditions are too cold for droplets to form and stay liquid.