Rare Fogbow White Rainbow Phenomenon Appears Over San Francisco Skies; How Is It Formed?

A San Francisco photographer captured an image of a rare aerial phenomenon over the hazy skies of California.

Fogbow Captured in San Francisco

Stuart Berman, a resident of San Francisco's Russian Hill district, took the image at Hawk Hill on the Marin Headlands peninsula. Berman shared the photo on his Twitter account.

Others who had also photographed fogbows sent pictures of them in response to Berman's tweet with the image.

One user reported having seen one earlier this year over Bodega Bay. Although he wrote that he had never ever heard of them, he was perfectly aware of what they were.

According to SFGate, Berman claimed to have observed it for around15 to 20 minutes, yet it was still present when he departed. He also discovered another one on the SCA Trail later that morning. If you're in the right spot at the right time, you might even be able to witness more fogbows while the fogy conditions last for the remainder of the week.

Rare Image of Fogbow Bow Assessed by a Meteorologist

According to National Weather Service meteorologist Brooke Bingaman, the photographer was in the ideal position because the sun was behind them.

He stated that if you look closely at the right side of the image, you can detect a reddish hue on the outside. It has some color, but the prisms don't work as well as typical raindrops do.

In reality, fogbows are not that uncommon, but Bingaman stated that it is hard to capture one on camera. He said, "What's rare is that someone would be around to capture it."

What Is a Fogbow?

A fogbow resembles a typical rainbow in some ways. But it forms when sunlight interacts with water droplets that are enclosed in fog, mist, or cloud, as opposed to raindrops, as it does in a traditional rainbow.

According to the Met Office, the water droplets are almost invariably less than 0.1 mm in diameter, making them substantially smaller than raindrops.

Fogbows appear to be colorless because of the several physical processes that the small droplets make the light go through, most notably diffraction. Because of this, fogbows are frequently referred to as white rainbows.

Another diffraction-related optical phenomenon known as glory is frequently observed with fogbows. A glory is a series of numerous, light-colored rings near the center of the bow.

How Do Fogbows Form?

A fogbow is made up of the same components as a rainbow, which include the sunlight behind the viewer and water droplets in front. Since the water droplets that make up fog are between 10 and 1000 times smaller than raindrops, the process of light diffraction by the droplet takes precedence, even if light still reflects off the droplet back towards the viewer.

Diffraction widens the reflected light beam, smearing out the colors and producing the distinctive ghostly white or very faintly colored fogbow. The fogbow is also significantly wider than a rainbow as a result of this.

In order for the light to travel through the droplets and produce the effect, the fog bank needs to be somewhat thin and dispersed. It has a similar effect as the cloud bows.

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