Multiple Supernumerary Bows
Images ©Ian Goddard, shown with permission.

Ian Goddard saw this rarity at Ashill in Somerset, UK on 7th August 2007.

The rainbow orientation is as in the smaller tilted image.

Purple and green fringes inside the primary bow are supernumeraries. They are caused by interference between pairs of light waves passing through rather small raindrops.

Supernumeraries are not always visible and when they are, only one or two are usually seen. In this rare sighting there are at least four in two fans where their spacing increases with height in the sky.

The fringe spacing increases with decreasing drop size and it is likely that the fans were produced by two localised rain showers in which the drop size changed with altitude.

Rain showers usually have a distribution of drop sizes resulting in supernumerary bows with a range of spacings which overlap to blur out all but the first one or two fringes. Here the drops at a given height must have been extraordinarily similar in size to allow four fringes to survive.

A similar display was seen at Statesville, North Carolina.