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Desert Fogbow ~ Imaged in the Sonoran Desert, Arizona by astronomy author Tom Polakis.

"We get fog in the Phoenix metro area only every several years. Today was a very good event, with visibility of only several hundred meters. I was surprised by this fogbow, which hung around at various levels of visibility for a half hour."

Image ©Tom Polakis, shown with permission
Appearance depends on the mean droplet size and the spread of drop sizes around the mean.

These IRIS program Mie scattering calculations show the effects of changing drop diameter.

When there is also a spread of drop sizes, the main bow becomes more diffuse and the supernumeraries less evident.

Fogbows are small droplet variants of rainbows.

Sunlight reflects internally from the droplet rear to form the primary bow.

As drop size becomes more and more comparable to light wavelengths, diffraction effects broaden the bow.

The refractions at ray entrance and exit produce colour separation as in the rainbow but the colours are increasingly diluted by the diffraction.