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| Lhasa Halos ~ Images by Xiaoshan Huang. A bright circumscribed halo, 22° halo and parhelic circle hang high like a huge eye in the Tibetan sky. From the horizon a colourful infralateral arc curves upwards and leftwards over the Potala Palace. All images ©Xiaoshan Huang, shown with permission |
| A mix of randomly oriented crystals (22° halo) and horizontal column crystals were probably entirely responsible for the display. Plate crystals contribute to parhelic circles but there is little evidence of a sundog that plates would also have generated. The circumscribed halo is made by rays passing through horizontal column side faces inclined 60° to each other. The more widely dispersed colours of the infralateral arcs are from rays passing between a near vertical end face and a side face. In effect, passage through a 90° prism. |
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| The circumscribed halo/tangent arcs change shape dramatically with sun elevation. |
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