OPOD - Lowitz at Yosemite

Last updated on September 16, 2023

OPOD - Lowitz at Yosemite: Exploring a Rare Atmospheric Phenomenon

In the realm of atmospheric optics, the occurrence of Lowitz arcs has long been a subject of fascination and debate. These captivating displays, characterized by a sharp and clear upper arc curving upwards from the 22° halo, have been a rarity to witness and photograph. However, thanks to the diligent efforts of photographers like Matthew Walker, we are now able to appreciate the beauty of Lowitz arcs in all their glory.

Lowitz arcs were first recorded in St. Petersburg, Russia in 1790. However, due to their infrequent and elusive nature, their existence was a matter of contention for many years. It wasn't until about two decades ago that these enigmatic optical phenomena were finally captured on camera, allowing scientists and enthusiasts to study them more closely.

The formation of Lowitz arcs can be simulated through the movement of ice crystals pivoting around a near-horizontal axis passing through opposite prism edges. However, this orientation is relatively improbable and inefficient in halo production, which may explain why these arcs are rarely observed with clarity. The scarcity of sightings has led to ongoing discussions and investigations into alternative explanations for their formation.

The classical model of Lowitz arcs assumes the presence of plate crystals with unrestricted rotational orientations. However, there is growing evidence suggesting that this model may be overly restrictive. Some displays have been better explained by proposing restricted rotation and the involvement of column crystals rather than plates. These column crystals rock back and forth about a Lowitz axis from a horizontal Parry orientation position, potentially contributing to the formation of the upper arc.

The mesmerizing Lowitz arc display captured by Matthew Walker at Yosemite offers valuable insights into the possible mechanisms behind these atmospheric phenomena. By utilizing HaloSim ray tracing, researchers have explored the likelihood of classically oriented Lowitz plates contributing to the observed phenomenon. The results provide intriguing possibilities for understanding the formation of these arcs.

As with many atmospheric optics phenomena, the study of Lowitz arcs is an ongoing pursuit. The analysis of real-world observations, combined with sophisticated modeling techniques, allows scientists to refine their understanding of the intricate processes occurring within our atmosphere. By unraveling the mysteries of Lowitz arcs, we gain deeper insights into the complexities and beauty of our natural world.

In conclusion, the captivating Lowitz arcs observed at Yosemite serve as a reminder of the remarkable optical displays that can grace our skies. Through the dedication and expertise of photographers and scientists alike, we continue to expand our knowledge of these elusive phenomena. As we delve further into the study of atmospheric optics, we unlock new discoveries and gain a greater appreciation for the awe-inspiring wonders that surround us.

Lowitz Arc at Yosemite

Matthew Walker of New Zealand captured this magnificent rare halo display over the High Sierra near May Lake at Yosemite, California - November 4, 2010. A sharp and clear upper Lowitz arc curves upwards from the 22° halo, crosses a tangent arc and touches an upper suncave Parry arc. ©Matthew Walker, shown with permission.

Lowitz arcs were first recorded at St Petersburg, Russia in 1790. From then on their very existence was argued about because they were rarely observed with any clarity and they were not finally photographed until about two decades ago.

Lowitz arcs can be simulated using ice crystals pivoting around a near horizontal axis passing through opposite prism edges. The orientation is improbably and is very inefficient in halo production. The latter might account for the paucity of observations.

The classical model assumes plate crystals and all rotational orientations are allowed. But there is little reason to be so restrictive. Some displays are a little better explained by positing restricted rotation and column crystals rather than plates.

The Yosemite display could have been produced by classically oriented Lowitz plates as shown in the HaloSim ray tracing at right.

Another possibility is that the upper arc was produced by column crystals rocking back and forth about a Lowitz axis from a horizontal Parry orientation position.

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