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Cloud bow

On December 23, I observed on Mt. Wendelstein (1838m, Bavarian Alps) my first real cloud bow which formed on the rim of a cumulus – or might be even a cumulonimbus – cloud. Although a snow shower had formed in the centre of the cloud, the bow clearly did not appear in the shower itself but on the outermost rim of the cloud. There, the cloud droplets must have been even big enough to make the bow show faint colours.

When the phenomenon started to appear, there was the left end of a rainbow visible at the rim of the shower, so it might have rained there. But the picture clearly shows how the droplets become rapidly smaller as the bow extends into the cloud. Even its diameter seems to be smaller in its upper part (123).