A smile in the sky

It was the most perfect October day, when the warm breath of summer still lingers, the last gasp before the chill of winter takes hold. We drove down to Gamlingay Wood for the afternoon, and while Pete and Chris hunted for insects, I soaked up the atmosphere - gold and orange leaves gently falling like raindrops, the last few butterflies (also orange and yellow) and wispy white clouds in a soft blue sky.

Unexpectedly, I arrived at a glade where the remaining leaves of the tall poplars had taken on a deep burnished  bronze hue. I looked up and was amazed to see an upside down rainbow, curving across the sky. I'm used to seeing sun dogs, but this was much more extensive. When I arrived home I discovered that I'd been lucky enough to spot a circumzenithal arc.

This is formed when sunlight refracts through horizontal ice crystals at such an angle that the light enters the crystal through its flat top face and exits through a side prism face causing the distinctive upside-down rainbow effect.  They are commonly associated with Cirrus clouds where ice crystals readily form, and these can also be seen in my image.


Circumzenithal arcs are actually quite common as these types of clouds occur throughout the year, however we only sometimes see them as they are usually obscured by clouds underneath. In order to be able to see a circumzenithal arc, a combination of atmospheric conditions must coincide just right. The height, depth and position of the ice clouds must be right as the cloud needs to be at a specific angle convex to the sun. The position of the observer is also important since its visibility can vary greatly over short distances. 


I took many other autumnal pictures, but have only added one, another view upwards of the gloriously yellow ash trees against the blue sky. If you want to join me on my woodland wander there are more images on Flickr starting here.