What we're seeing are temperatures that
start off quite cold and then when the sky clears
they drop fairly rapidly.
If that conditions persists for a few days, the ground chills, gets quite cold
The ground itself is radiating
away the heat into space, into clear space.
And by getting very cold on the surface, you chill the atmosphere
that's next to this very cold snow.
This lower layer that's getting very cold under the clear sky conditions is denser and it starts
to slide down this huge dome of Antarctica.
What you need is a place where that air is actually caught
and held for a while. So by causing the
air flow to be stationary for an extended period, you get
the absolute lowest temperatures that we're able to find.