On November, 23rd, 2016, I observed in Altocumulus virga a sun pillar from Mt. Zugspitze which exhibited a certain amount of inclination with respect to the otherwise common vertical direction. At first it appeared rather diffuse, but later on the distinct tilt became clearly visible.
That morning was relatively warm with temperatures around –3°C on the 2963 meter high summit, and a squally foehny wind gusted with peaks up to 80 km/h. Warm air was sucked from the Mediterranean sea by a severe southern air current. I suspect that this wind led to the inclination of the sun pillar by systematically tilting the ice crystal axes into a preferential direction.
There are only a few similar observations that can be found in the literature. On January 1st, 1969, K. Lenggenhager documented a tilted and split lower sun pillar in diamond dust on the Mt. Säntis (2502m). He explained the phenomenon by air currents which were forced to ascend a ridge, and the crystal axes being turned by various amounts on different levels of altitude (see graphic from [1]).
Similar conditions might have prevailed in my observation. The air masses of the Mediterranean sea were forced to ascend the Alps, and therefore they might have tipped the crystal axes increasingly with rising altitude.
Sun pillar in original and with unsharp mask
Another oblique sun pillar was described by Edgar W. Wooland after an observation in Boulder, Colorado [2] on January 10th, 1918, and I myself could also already observe oblique and displaced halos [3]. Unfortunately, there seem to be no further documented cases.
Any appropriate notes on the subject are highly welcome.
References
[1] K. Lenggenhager: “Seitlich verschobene, umschriebene Halostücke, schräg ovaler Halo und schräge Lichtsäulen”, Archiv für Meteorologie, Geophysik und Bioklimatologie, June 1977, Volume 26, Issue 2, pp 275–282
[2] Edgar W. Woolard: “The Boulder Halo Of January 10, 1918”
[3] Claudia Hinz: “Double Halos”
Author: Claudia Hinz