0 a night or the time in winter at places close to the North or South Pole, when the sun does not appear above the horizon
A woman in the polar night.
Activity is at a stand-still during the polar night, which lasts for many months.
Inside the polar night jet is the polar vortex.
Below this barrier exists the polar night jet, which is weak in the early winter, so any descending polar air mixes with the mid-latitudes.
Further, there is no interference from the sun in the millimeter range during the months of polar night.
However, at the outer boundary of the polar vortex, in winter, the stratospheric polar night jet exists.
Each kind of polar night is defined as when it's darker than the corresponding kind of twilight.
The opposite phenomenon, polar night, occurs in winter when the sun stays below the horizon throughout the day.
