

Multiple supernumerary bows. The supernumeraries are the closely spaced greenish purple arcs on the inner (blue) side of the primary bow. Captured by Mark Nankman at Hedeviken in Sweden after a heavy shower, August '99. ©Mark Nankman, shown with permission.

Supernumeraries are created by small, almost same sized raindrops. The diagonal inset on this contrast enhanced view is an AirySim simulation calculated for drops of 0 .7mm mean dia. with only an 8% (std. dev.) spread in diameters. Look slightly inside a bright primary bow and sometimes you will see one or more predominantly green, pink and purple fringes. Their numbers and spacing can change from minute to minute. They are seen most often near the top of the bow - example here .



These "supernumerary bows" are an intimation of the limitations of geometric optics for it is totally unable to explain them. To do so we must take account of the wave nature of light.









