Moments in the life of a circumzenithal arc

Last updated on September 16, 2023

Moments in the Life of a Circumzenithal Arc

The beauty of circumzenithal arcs lies in their fleeting nature, capturing our attention with their ethereal appearance. These optical phenomena manifest as vibrant bands of color in the sky, appearing briefly before disappearing, only to reappear once more. The video footage showcases their mesmerizing dance, where multi-layered cirrus clouds intersect with plate crystals, allowing them to glimmer in brilliant hues towards the observer.

Circumzenithal arcs, or CZAs for short, exhibit a unique characteristic compared to other halos - they seem to change, shine, and fade at a faster pace. This rapid transformation can be attributed to their position near the zenith, the point directly overhead. In this region of the sky, clouds and crystals move swiftly, traversing the celestial canvas with remarkable speed.

The Ephemeral Nature of CZAs

CZAs epitomize the transitory nature of atmospheric optics. They materialize for brief moments, tantalizing viewers with their vibrant display before vanishing from sight. However, their disappearance is only temporary, as they soon reemerge with renewed brilliance. This cycle of appearing and disappearing adds to the mystique surrounding these captivating arcs.

The Influence of Plate Crystals

Plate crystals play a crucial role in the formation of CZAs. These ice crystals assume a flat, plate-like shape, ideal for creating the conditions necessary for light refraction and dispersion. When sunlight interacts with these crystals, it undergoes intricate processes that result in the stunning colors observed in CZAs.

The Sweet Spots of the Sky

CZAs form in specific regions of the sky known as "sweet spots." These areas are where plate crystals align perfectly with the incoming sunlight, allowing for optimal refraction and dispersion. When these sweet spots intersect with cirrus clouds, a magical display unfolds, as the CZAs momentarily reveal their vivid hues to those fortunate enough to witness them.

The Dance of Light and Clouds

As the cirrus clouds and plate crystals glide across the sky, they create a dynamic interplay of light and shadow. This dance between the atmospheric elements contributes to the ever-changing nature of CZAs. The rapid movement of the clouds and crystals near the zenith enhances the ephemeral quality of these arcs, captivating viewers with their fleeting beauty.

A Delicate Balance

The existence of CZAs relies on a delicate balance between atmospheric conditions. The presence of cirrus clouds and the precise alignment of plate crystals are essential factors for their formation. Even slight variations in these elements can affect the visibility and intensity of CZAs, making their appearance all the more remarkable when they do grace the sky.

The Zenith's Role

The zenith, the point directly overhead, serves as a stage for CZAs to perform their mesmerizing act. Being in close proximity to this pivotal point in the sky allows CZAs to exhibit their characteristic quicksilver behavior. The swift movement of clouds and crystals near the zenith amplifies the sense of motion and transience associated with these arcs.

The Enigmatic Charm

CZAs possess an enigmatic charm that captivates both casual observers and avid sky gazers alike. Their evanescent nature, combined with their vibrant colors, evokes a sense of wonder and awe. The brief moments when CZAs grace the sky become treasured memories, etching themselves into the minds of those fortunate enough to witness their ethereal splendor.

In conclusion, circumzenithal arcs are ephemeral masterpieces that grace the sky for fleeting moments. Their existence relies on a delicate interplay between cirrus clouds and plate crystals, creating a captivating display of colors near the zenith. Their transient nature and ever-changing appearance make CZAs a true marvel of atmospheric optics, leaving observers in awe of the wonders that unfold above us.

Moments in the life of a circumzenithal arc by Olivier Vandeginste (site, cza). �Olivier Vandeginste, shown with permission.

More vividly than a thousand stills the video captures the ephemeral "once here, next gone, then back again" character of circumzenithal arcs. Multi-layered cirrus crosses the sweet spots in the sky where plate crystals can, just for a moment, glint their CZA colours towards the eye. The arc hints its presence, blazes with full brilliance only to fade and then shine forth once more.

CZAs seem to alter, shine and fade more quickly than other halos. Their position near the zenith is responsible. There, clouds and crystals sweep more quickly across the sky than elsewhere.

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

If you use any of the definitions, information, or data presented on Atmospheric Optics, please copy the link or reference below to properly credit us as the reference source. Thank you!