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| Cloudbow/Fogbow Naas, Co. Kildare, Ireland imaged by Simon Holt. ©Simon Holt, shown with permission. Cloudbows and fogbows are the small droplet analogue of rainbows. They are sky scale diffraction patterns. Superimposed on the right hand side (Simon's complete image is below) is a droplet scattering calculation using Mie theory and IRIS. The best fit water droplets were 150 micron (0.15mm) diameter. The inner supernumeraries allowed the spread in diameters to be estimated - this came out at 10% (standard deviation for a Gaussian distribution). Thus the drops making this splendid bow were large! Cloud and fog droplets range usually in size from 1 - 100 micron but the mean is usually 10-20 micron. Sometimes large droplets, possibly also virga, in moisture laden air produce a faint cloudbow without any perceptible mist or rain. This one is a spectacular example. "There was no rain, though the air was damp and the clouds had a feathery texture to them." |
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