Circumzenithal Arc - Yorkshire, England

Last updated on September 16, 2023

Circumzenithal Arc - A Spectacular Atmospheric Phenomenon in Yorkshire, England

When it comes to atmospheric optics, one of the most captivating and awe-inspiring phenomena is the Circumzenithal Arc (CZA). This optical marvel, often referred to as the "upside-down rainbow," can occasionally be spotted in the skies above Yorkshire, England. While rainbows are a common sight after a rain shower, the CZA is a rare and fleeting spectacle that leaves onlookers in awe of its vibrant colors and ethereal beauty.

What is a Circumzenithal Arc?

A Circumzenithal Arc is an atmospheric optical phenomenon that occurs due to the refraction and reflection of sunlight by ice crystals present in thin, wispy cirrus clouds. These ice crystals act as tiny prisms, bending and dispersing the sunlight into its constituent colors. Unlike rainbows that form when sunlight interacts with water droplets, CZAs are formed by the interaction of sunlight with ice crystals.

How Does a Circumzenithal Arc Form?

To witness a Circumzenithal Arc, specific atmospheric conditions need to be met. First and foremost, there must be high-altitude cirrus clouds present in the sky. These clouds are composed of ice crystals that are aligned horizontally, resembling thin sheets or feathers. As sunlight passes through these ice crystals, it undergoes refraction, bending at specific angles. The sunlight then undergoes internal reflection within the ice crystals before exiting at a different angle. This intricate process results in the formation of a Circumzenithal Arc.

The Stunning Appearance of a Circumzenithal Arc

CZAs are known for their striking appearance, often described as an "upside-down rainbow" due to their shape and orientation in the sky. They typically appear as a vibrant band of colors curving upwards from the zenith, creating an arc that seems to defy gravity. The colors of a CZA are similar to those of a rainbow, with red on the outer edge and violet on the inner edge. However, CZAs are usually more vivid and intense in color than rainbows, adding to their allure.

The Transient Nature of Circumzenithal Arcs

Circumzenithal Arcs, like many other atmospheric optical phenomena, are transient and short-lived. They can appear for just a few minutes or even seconds, making them a rare sight to behold. Therefore, spotting a CZA requires both favorable atmospheric conditions and a bit of luck. It is crucial to keep an eye on the sky, especially when cirrus clouds are present, as CZAs can quickly come and go.

Other Optical Phenomena Associated with Circumzenithal Arcs

CZAs are often accompanied by other atmospheric optical phenomena, further enhancing their visual impact. Some of these associated phenomena include:

• Supralateral Arcs: These arcs form parallel to the horizon, intersecting the Circumzenithal Arc at both ends.
• Tangent Arcs: Tangent Arcs appear as short arcs tangent to the top of the Circumzenithal Arc.
• Parhelic Circle: This circular band of light encircles the entire sky at the same altitude as the sun.

The combination of these various optical phenomena creates a mesmerizing display in the sky, leaving observers in a state of wonder and amazement.

Capturing the Beauty of Circumzenithal Arcs

For those lucky enough to witness a Circumzenithal Arc, capturing its beauty through photography can be a rewarding experience. To photograph CZAs effectively, it is essential to use a wide-angle lens to capture the entire arc. Additionally, adjusting the exposure settings to bring out the vibrant colors is crucial. Patience and persistence are key when attempting to photograph this elusive phenomenon, as CZAs may appear and disappear rapidly.

The Significance of Circumzenithal Arcs

Beyond their visual appeal, Circumzenithal Arcs have scientific significance as well. By studying the formation and properties of CZAs, scientists can gain insights into the characteristics of ice crystals present in the upper atmosphere. This knowledge contributes to our understanding of atmospheric processes, climate patterns, and the behavior of light in different atmospheric conditions.

Conclusion

The Circumzenithal Arc is a truly remarkable atmospheric phenomenon that graces the skies above Yorkshire, England, on rare occasions. Its captivating appearance and vibrant colors make it a sight to behold and cherish. While its transient nature adds an element of mystery, witnessing a CZA can be an unforgettable experience. So, keep your eyes on the sky, and who knows, you might just catch a glimpse of this enchanting upside-down rainbow painting the heavens above Yorkshire.

CZA fragment at Gilling East, Yorkshire, England. Imaged by Gill & Adrian Smith on 31st January 2003 '00. CZAs like all halos can be transitory, this one lasted for only about two minutes.

�2003 Gill & Adrian Smith, reproduced with permission.

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Reference Atmospheric Optics

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