photo #4206567

Stephanie Morton (Member Cloud Appreciation Society) spotted this fogbow on the first day of Northern-Hemisphere summer from the beach at Ocean Shores, Washington, US. Like a rainbow that formed without any rain, a fogbow is caused by sunlight reflecting back off the tiny water droplets in fog. At less than 0.1 mm across, these droplets of low cloud are far smaller than raindrops, which might be 1 mm or more across. Their diminutive size explains the fogbow’s lack of any clear colours. As well as refracting the sunlight passing through and so separating its wavelengths into a spectrum of colours, the tiny fog droplets also scatter the sunlight by the process of diffraction – and much more so than larger raindrops do. This has the effect of blurring the colours back together again. It means that fogbows tend to look more blurred and broad than their rainbow cousins, and they have washed-out colours – sometimes, so washed out as to appear completely white.