Tail Tales

Last updated on September 16, 2023

Tail Tales: Exploring the Mysterious Curved Tails Below Subsuns

Atmospheric optics never ceases to amaze us with its captivating displays. One such phenomenon that has left both photographers and scientists intrigued is the presence of curved tails below subsuns. Subsuns are formed when sunlight reflects off the near-horizontal faces of plate-shaped ice crystals in the atmosphere. These curved tails, however, pose a puzzling mystery that has yet to be fully unraveled.

In the case of two separate instances captured by photographers Jerry Xiojin Zhu and Raymond L. Lee, the aircraft was flying at a relatively low altitude when these peculiar phenomena were observed. The photographers managed to capture several images, allowing for a closer examination of the phenomenon.

While window scratches can sometimes create similar effects, it is evident that this is not the case in the images under scrutiny. One possible explanation for the curved tails is the presence of ice crystals tilted from the horizontal within the aircraft's airstream. These tilted crystals could potentially scatter light in a manner that creates the distinctive curved shapes observed.

However, there is a challenge in understanding this phenomenon fully. By measuring the angular length of the light streaks, considering the camera shutter speed, and estimating the airplane's airspeed, it is possible to calculate the distance at which the glinting ice crystals are located. Astonishingly, in both cases, these crystals were found to be approximately 40-60 meters away. To put this into perspective, the wingtip distance of a Boeing 737 aircraft, like the one Raymond L. Lee was on, is only 15 meters. This observation suggests that trailing wingtip vortices can be ruled out as the cause of these mesmerizing tails. The glinting crystals are clearly situated well beyond the reach of the aircraft's wingtips.

Despite these findings, the exact mechanisms behind the formation of these enigmatic tails remain uncertain. Scientists and researchers continue to explore various hypotheses and possibilities to shed light on this intriguing atmospheric phenomenon. Acknowledgements are due to Raymond Lee and Walter Tape for their invaluable discussions and ideas in the pursuit of understanding this phenomenon further.

In conclusion, the presence of curved tails below subsuns continues to captivate our curiosity. While we have made progress in identifying potential causes, the exact nature of these tails remains shrouded in mystery. As we delve deeper into the realm of atmospheric optics, it is these enigmatic phenomena that remind us of the endless wonders that await our exploration.

Subsun 'Tails'

Large images: Jerry Xiojin Zhu (site) near Chicago December '04. ©Jerry Xiojin Zhu, shown with permission.

Small image: Raymond L. Lee (site) during a descent into London, England June '97. ©Raymond L. Lee, shown with permission.

In both cases the aircraft was quite low. Each photographer took several images.

Subsuns are produced by reflection from the near horizontal faces of plate shaped ice crystals. The curved tails below the subsuns are unusual. Window scratches can produce similar effects but that is not the case in these images.

A possibility is that the tails are produced by crystals tilted from horizontal in the aircraft airstream.

There is a problem! By measuring the angular length of the light streaks, knowing the camera shutter speed and estimating the airplane airspeed, the distance of the crystals producing the glints can be calculated. In these two separate cases they are 40-60m away. By comparison, the wingtip distance of a 737 (Lee's aircraft) is only 15m which somewhat rules out trailing wingtip vortices. The glinting crystals are well beyond the wingtips. The causes of the tails are uncertain.

Acknowledgements to Raymond Lee and Walter Tape for discussions and ideas.

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