Atmospheric
Optics
About - Submit Optics Picture of the Day Galleries Previous Next Today  
               
Fogbows & Polarization

Fogbow, its supernumeraries and the central glory imaged by Boris Borisovich ( journal ) at the top of Mt. Kukisvumchorr in the Khibiny mountains, Kola Peninsula, Arctic Russia.

The main bow is the broad white segment at top right. The highly coloured supernumeraries, strangely split and staggered from left to right are the result of viewing through a polarizing filter. Fogbows, like rainbows are strongly polarized.

Image ©Boris Borisovich, shown with permission



Two refractions and a reflection make a fogbow.

Polarization occurs at each step.

Light interacting with a water or glass surface.

Polarized light with its electric vector parallel to the surface is shown in red. Vectors at right angle are in blue.

Parallel electric vectors are weakened by refraction.

Perpendicular vectors are weakened by reflection.

A Fogbow Dissected

Top band – A section through a fogbow for perpendicularly polarized light. The main bow is strong. Highly coloured supernumeraries fill the space inside it towards the central glory. The right hand of Boris’s image resembles this.

Centre - The main bow is almost absent in parallel polarized light. The supernumeraries are shifted in position. Compare to the left hand of the image.

Lowest band – The two polarizations combined. The two shifted sets of supernumeraries almost cancel.

Use a polarizing filter to see strong fogbow supernumeraries but expect a strange kinked appearance.

Mie theory simulations for 20 micron diameter droplets adapted from Philip Laven’s MiePlot.

Unpolarized light from the sun, electromagnetic radiation, has oscillating electric fields pointing equally in all directions (at right angles to that of travel).

That changes when the light hits the watery surface of a fog droplet.

The reflected light is strongest when its electric fields are parallel to the surface.

Refracted rays into the water are strongest with the fields perpendicular.

Light leaving droplets to form a fogbow and glory is polarized.

Look at a fogbow (or rainbow) through a polarizing filter and it changes dramatically as the filter is rotated – try it!