Fog bow
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The fog arc (also white rainbow ) is an appearance of the atmospheric optics in the form of a circular, white glowing arc. It is a special form of the rainbow , which is caused by particularly fine droplets.
observation
An arc of fog occurs when the sun shines on a wall of fog and the light is reflected by the drops, which are at least 5 micrometers in size. Compared to the rainbow, the ribbon of the fog arc is roughly twice as wide and the incident white light is not refracted into different colors. The arc of fog is always opposite the sun. Its radius is up to 42 ° and becomes smaller as the droplet size decreases. If the droplets are smaller than 5 micrometers, the arc of fog can no longer be seen with the naked eye. For observation, it is also necessary as an observer to stand in front of the fog wall with the sun behind you, otherwise the light is already too weakened by the fog.
Often the fog arc can be observed together with the Brocken Ghost and the Glory .
Emergence
The creation principle is based on the one hand, as with the rainbow, on the refraction and reflection of light rays in the water droplets of the mist. Since the droplets are smaller than 50 micrometers , diffraction effects also play a role. The small droplet size means that the reflected light rays are superimposed so that the arc appears white.
The smaller the droplets, the fainter the fog appears. From a droplet size of around 5 micrometers, the light becomes so weak that it can no longer be perceived.
