Fallstreak Hole and Circumzenithal Arc over Hong Kong

March 22, 2022


Photographer: Li Yuen Han

Summary Authors: Li Yuen Han; Cadan Cummings

The photo above features both a fallstreak hole and circumzenithal arc observed from Jordon, Hong Kong. Fallstreak holes, also referred to as hole punch clouds, are created when a cloud layer composed of supercooled water droplets is unsettled and produces ice crystals. This phenomenon is often caused in cirrocumulus or altocumulus clouds by jet aircraft that pass through a cloud deck producing turbulent air behind their wings and engines. As the ice crystals nucleate, the surrounding water evaporates and ice crystals slowly fall to the ground to form this unique circular hole in the cloud. Looking at the center of the cloud hole, one can also see a faint circumzenithal arc. These two phenomena are likely correlated because as the ice crystals accumulate in the air, they act like a prism and refract incoming light to produce what looks like an upside-down rainbow. Photo taken December 9, 2021.


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