A fogbow (or mistbow) is a mainly pale white arc visible on the opposite the light of the light source. A faint redness may appear on the edges. The phenomenon is visible either in the fog or within a cloud of mist just above the ground.
There is theoretically no clear border between the fog arc and the rainbow, but the rainbow gradually turns into a fog arc as the droplet size decreases. The smaller the droplets, the smaller the radius of the arc, the thicker it is and the more white begins to dominate it.
Usually, making a distinction between a fog arc and a rainbow is easy, but intermediate shapes can sometimes appear. If the main arc has a clear colors of the spectrum and isn't white, it is a rainbow. If, on the other hand, the arc is dominated by white and some of the colors in the spectrum are missing, it can be interpreted as a fogbow.
Two fogbows have been observed - the primary fogbow and the secondary fogbow. Usually only the main fogbow is visible. One or very rarely more interference arcs can sometimes occur inside the main fog arc. They can be more colorful than the main arch.
Fogbows are seen even in frost in winter, as small mist droplets can be in liquid form up to -40 ° C.
From time to time, an arc resembling a fogbow stands out in a distant clouds. In this case, we are talking about a cloudbow. The cloudbow is considerably rarer than the fogbow and has its own phenomenon identification in the Skywarden's list of rare light phenomena.
Fogbow in faiding mist. Image by Mauri Korpi.
Fogbow. Photo by Päivi Kuljunlahti.
This image is an ecellent example that shows how fogbow can be seen around the watcher's head at antisolar point. Image my Olli Sälevä.
An even fogbow showing a slight supernumerary bow inside the darker inner zone of the arc. Photo by Seija Ropponen.
Fogbow at winter time. Image by Mikko Peussa.
A bright fogbow on mist floating abowe the ground. An outer secondary fowbow is present above the primary arc. Photo by Anna-Liisa Sarajärvi.
The sharp lines of the arc form shows that the nist driplets must have been relatively big in size. Image by Antti Peuna.
A rainbow or a fogbow? The sun below the horizon gives a red shade to the arc. The redness hides the original colors of the arc, which makes the classification hard. The observer describes small droplets that appeared on the car's windshield at the temperature of -15 C. Image by Olli Sälevä.