OPOD - Circumzenithal Arc, Yorkshire

Last updated on September 16, 2023

OPOD - Circumzenithal Arc, Yorkshire: Exploring the Queen of Ice Halos

The atmospheric phenomenon known as the circumzenithal arc, often mistaken for a rainbow, is a breathtaking sight that can be observed in certain conditions. Recently, Mike Sharpe captured a magnificent image of this phenomenon at Richmond, North Yorkshire, UK, showcasing its mesmerizing beauty. In this article, we will delve deeper into the intricacies of the circumzenithal arc, exploring its characteristics and shedding light on its elusive nature.

The circumzenithal arc is characterized by its ephemeral nature, as it appears and disappears within seconds. Positioned near the zenith, this arc is formed by ice crystal cirrus clouds that swiftly move across the sky. These clouds create a dazzling display of colors, making the circumzenithal arc one of the purest and brightest halos in the atmospheric optics realm.

To understand the formation of the circumzenithal arc, we must examine the ice crystals responsible for its creation. These crystals, known as plate crystals, align themselves with their large hexagonal faces parallel to the ground. This alignment is crucial for the aerodynamic drag that shapes the crystals and contributes to the arc's distinct appearance. When sunlight passes through these aligned plate crystals, it enters through their upper face and exits through a vertical side face, resulting in a unique optical phenomenon.

The circumzenithal arc acts as a natural laboratory for studying the dispersion of light. The collimated light passing through the aligned plate crystals mimics the behavior of light passing through a clamped 90° prism. This natural demonstration provides a remarkable opportunity to observe the dispersion of light and the formation of dark Fraunhofer lines within the spectrum.

As we explore the captivating world of atmospheric optics, it is important to note that this article has been automatically converted from an older version and may not appear as intended. For the original article, you can refer to the link provided.

In conclusion, the circumzenithal arc is a captivating atmospheric phenomenon that often leaves observers in awe of its beauty. Its ephemeral nature, vibrant colors, and unique formation process make it a sight to behold. By understanding the alignment of plate crystals and the dispersion of light, we can appreciate the intricate mechanisms behind this extraordinary optical display. Next time you find yourself gazing at the sky, keep an eye out for the queen of ice halos, the mesmerizing circumzenithal arc.

Queen of the Ice Halos

Mike Sharpe imaged this magnificent circumzenithal arc at Richmond, North Yorkshire UK.

©Mike Sharpe, shown with permission.

The circumzenithal arc, oft mistaken for a rainbow, can be ephemeral. Always close to the zenith, the ice crystal cirrus clouds forming it scud across quickly, brightening and then dimming the arc in seconds.

It has the purest and brightest colours (with its matching circumhorizon arc) of all the halos.

Plate crystals generating it are aerodynamic drag aligned with their large hexagonal faces usually within a degree or better of horizontal. Nearly parallel sun rays stream into the upper face and leave through a vertical side face. Nature creates an almost ideal laboratory spectrum demonstration where collimated light shines through a clamped 90° prism. Have dark Fraunhofer lines ever been observed in a CZA?

Note: this article has been automatically converted from the old site and may not appear as intended. You can find the original article here.

Reference Atmospheric Optics

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