Dewbow (w-657-24)

In gallery: Photos of the month (2005)
Related photos: Atmospheric optics Light in water droplets Dew bow

This bright dewbow formed in a field with clovers, near the river Rio Grande in Socorro, New Mexico (USA). A dewbow is nothing else than a rainbow, but here the water droplets are on the ground (usually on a field of grass or some other vegetation). Also, dew droplets are smaller than the raindrops in storms, so the bow appears wider with less saturated spectral colors.

Dewbows are uncommon, especially clear dewbows such as the one on the photo. There are various reasons for this: 1) the dew droplets must be perfectly round, so the plant on which the dew forms must be either waxy or have very fine hairs on the leaves that support round droplets; 2) the dew droplets must be relatively small, otherwise the droplet number density is too low to produce a clear dewbow; 3) dew disappears quickly after sunrise, especially the more suitable small droplets; 4) If the sun is low, the effective sunlit area on a field is low due to the long shadows; 5) a field with plants such as grass has lots of detailed structure, which mask any slight coloration visible; 6) the amount of dew must be optimal - there may not be too much (this will result in larger and fewer droplets, or plants soaked in water) or too little (not enough droplets or too small droplets to form a clear colored bow); 7) the field must be large, and you must be standing at some distance, to notice a clear dewbow. Considering all these factors that must come into play to form a nice dewbow, it is understandable that dewbows are a relatively rare occurrence, especially the obvious bows.

Photographed in the morning of October 12, using a Nikon FE with Fujichrome Provia 100F film, and a 28mm wide-angle lens with linear polarizer filter. Unfortunately the field with clovers, which proved to be an excellent source for dewbows, was cut down a few weeks later.