Thanks for the images issued recently on the period.
We have on the same say the 14th dec, the feature showed by different observers.
If we examine carefully the pattern of such, the feature looks circular all around the pole itself with unequal brightnesses.
I am concluding the following:
- such protusions exhibited initially by C.Foster look artefact at final,
- the bright ring showed on photo is rather well centered on the pole itself,
- this looks as the first diffraction ring of the pole acting like an airy disk of a star.
The pole is so bright that the diffraction is creating this ring even on the dark sky, making apparent protusions, 
on the planet disk itself which is more or less darker, showing lighted arc.
Stange to see also visually at the terminator the lighted extension, better on the blue color
 (the pole is also blue intense on this).
As a conclusion: a diffraction effect well collected by observers and not an any atmospheric event.
I inserted 2 images being the more representative. Sorry for the disturbance.
[Stanislas Maksymowicz  Ecquevilly,France]