Sun pillars are a captivating atmospheric optical phenomenon that occurs when sunlight interacts with ice crystals in the atmosphere. These pillars appear as vertical columns of light extending above or below the sun, creating a stunning visual display. However, in some rare cases, sun pillars can exhibit additional features known as "echo" arcs, making them even more extraordinary.
One such remarkable occurrence was captured by Jon Inghram on November 12th, 2010, near Stockton, Kansas. Inghram's photographs revealed a sun pillar topped by an upper tangent arc, accompanied by faint echo arcs on each side. This sighting was only the second recorded instance of sun pillar echoes, making it an exceptional achievement in careful observation.
To confirm the authenticity of these echoes, it is crucial to capture multiple images of the event over several minutes. This approach helps distinguish them from mere cloud patches or streaks. By comparing the photographs, any camera artifacts caused by hand-holding or shooting through windows can be identified and eliminated from consideration.
Despite their rarity, these echo arcs remain unexplained phenomena. Further observations are needed to determine their full extent and establish their dependence on solar altitude. Interestingly, both known instances of echo arcs occurred at the same sun height of 1°, hinting at a possible connection between this specific solar position and the formation of these enigmatic arcs.
Attempts to attribute the pillar echoes to wobbly, highly flattened pyramidal plate crystals, similar to those implicated in elliptical halos, have not yielded convincing results. Ray tracings using such crystals fail to reproduce the observed phenomena accurately. Therefore, alternative explanations must be sought to unravel the secrets behind these captivating echoes.
Sun pillars themselves are believed to arise from large ice crystals, often possessing imperfections and snowflake-like appendages. These crystals may feature tilted facets caused by steric hindrance and exhibit peculiar gyratory motions as they descend through the atmosphere. Simulating these complex crystal structures requires different approaches, and the models developed thus far have a degree of arbitrariness.
Understanding the formation of both sun pillars and echo arcs is essential for developing credible explanations for these phenomena. While elliptical halos share some similarities with sun pillars, they too present their own set of intriguing questions. By scrutinizing sun pillars with keen eyes, we may uncover unexpected surprises and shed light on the underlying mechanisms driving these optical marvels.
In conclusion, the discovery of sun pillar echoes adds a new layer of fascination to the study of atmospheric optics. The rarity and unexplained nature of these phenomena make them a subject of great intrigue for scientists and observers alike. By continuing to document and analyze these occurrences, we can hope to gain deeper insights into the complex interplay between sunlight and ice crystals in our atmosphere. So, keep your eyes on the sky and be prepared for the unexpected – you never know what secrets the heavens might reveal!
Sun Pillar Echoes ~ This tall sun pillar topped by an upper tangent arc has something more. On each side are faint "echo" arcs. These are exceeding rare having only been recorded once before. This is one of 13 images by Jon Inghram taken near sunset on 12th November 2010 east of Stockton, Kansas. A triumph of careful observation. All images except otherwise labelled ©Jon Inghram, shown with permission
It pays dividends to take several images of an unusual event, preferably with a hand-held camera.
A single image of these echoes could easily have been disregarded as due to unusual patches of cloud. Multiple pictures over several minutes help decide against cloud patches and streaks. Hand holding helps identify camera artefacts. Shooting through windows is a good source of artefacts.
At right - Five images stacked together, better to show the rare arcs.
The arcs are unexplained. We need more observations to establish their full extent and dependence on solar altitude. The only two known observations were both at the same sun height of 1�.
It's tempting to ascribe the pillar echoes to wobbly, highly flattened pyramidal plate crystals similar to those invoked for elliptical halos. However, ray tracings using them are not convincing.
Sun pillars are thought to be sometimes made by large plates with imperfections and even snowflake like appendages. These could have tilted facets due to steric hindrance and drift downwards with peculiar gyratory motions. They would require different simulation approaches and such models have an uncomfortable degree of arbitrariness. However, a credible explanation is needed both for these pillars and to some extent also for elliptical halos themselves.
Look carefully at sun pillars - they might have surprises!
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HaloSim ray tracings for flattened pyramidal plate crystals.
Left: Crystals with a pyramidal upper face and flat lower one.
Right: Hexagonal pyramids on upper and lower faces.
Neither simulation reproduces the two sightings at all well.
December 23, 2001 Finland
The first and only previous known observation. The pillar echoes were seen at Espoo and Kotka near the southern coast of Finland by Mika Sillanp��, Eero Savolainen and Jukka Ruoskanen. Each photographed them.
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"Sun Pillar Echoes - OPOD". Atmospheric Optics. Accessed on December 10, 2023. https://atoptics.co.uk/blog/sun-pillar-echoes-opod/.
"Sun Pillar Echoes - OPOD". Atmospheric Optics, https://atoptics.co.uk/blog/sun-pillar-echoes-opod/. Accessed 10 December, 2023
Sun Pillar Echoes - OPOD. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/sun-pillar-echoes-opod/.