Sphere
Columns
Needles
Plates
Solar particles collide with Earth's atmosphere
Lunar cycles
Magnetic field fluctuations
Relatively low surface temperature
Wind sculpting snow into sharp ridges and grooves
Animal tracks in deep snow
Melting and freezing snow
Melting and refreezing of snow
Ground that remains completely frozen for at least two consecutive years
A permanently frozen lake or pond
Snow that falls in spring
The top layer of snow on mountains
A period in polar regions where the sun does not rise for more than 24hours
A cold front coming from the polar regions
A night when the Aurora Borealis is visible
A night where the polar bears come down to towns