Lower Pillar & Subsun

Neville Richardson imaged this very extended and narrow lower sun pillar at Tignes, France looking from the Aiguille Percee. "..the air temperature was around –18C and the air was full of tiny, single crystal ice particles." Taken early afternoon, the sun elevation was 22°.

©Neville Richardson, shown with permission.
Atmospheric
Optics
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Both the lower sun pillar and the subsun (the bright patch at the base of the pillar) are produced in the same way. Sun rays reflect from large hexagonal faces of plate shaped ice crystals. Pillars can also be made by horizontal columns. In this case the crystals were floating in the subzero air as 'diamond dust'.

The reflection from plates can be from the exposed upper face or internally from the lower one.

The extent that the crystals wobble around their equilibrium horizontal orientation determines what is seen. Large wobbles produce tall pillars, very small wobbles give a subsun - very nearly a disk like reflection of the sun the same distance below the horizon as the sun is above it.