(I mean, of course, in the Northern Hemisphere.) Shouldn’t it start getting warmer at that point, as the days lengthen and the sun’s light strikes the Earth a bit more directly every day?
Because the ground and water take longer to cool than the air: big honkin’ heat sinks.
Is there any reason why the days immediately after the Winter Solstice have to be long enough for net warming to occur? After all, it must take a while for heat to be conducted/radiated out of the ground and water.
Plus, once the ground is covered with reflective white snow and ice, it doesn’t absorb heat as readily.
There are two parameters to consider:
#1. the rate at which the northern hemisphere is radiating heat out to the universe. Assuming other factors are held steady, this is a function of the temperature of the earth and the temperature of the surrounding universe.
#2. the rate at which the sun is dumping heat into the northern hemisphere.
at winter solstice, solar heating of the northern hemisphere is at its minimum, but #1 is still of greater magnitude than #2. if we magically halted the earth at the winter solstice position, the northern hemisphere’s temperature would continue to drop. How far? You’d have to ask a climatologist, I suppose.
Since #1 is still greater than #2 at winter solstice, the temperature doesn’t stop dropping until well after the solstice, when #2 has increased to the point where it is equal to #1.
If the earth orbited the sun really, really slowly, then the earth would cool off a lot more before the solstice, coming much closer to equilibrium with the rest of the universe, reducing #1 to a value very close to #2. In that scenario, the lowest temperature would happen much sooner after the solstice than it does now (but it would also be much lower).
Yup. A couple of articles which note this:
From National Geographic:
From Chicago Tribune / WGN meteorologist Tom Skilling:
Also, just to note that, while the Winter Solstice is the beginning of “astronomical winter”, it doesn’t line up well with the meteorological definition of winter. “Meteorological winter” is usually defined as the months of December, January, and February in the northern hemisphere; it’s the period which is most closely associated with wintry weather. The coldest part of the year, in most places, tends to fall right in the center of meteorological winter (i.e., in early to mid January).
In brief: Less than 12 hours daylight and more than 12 hours night means the hemisphere is still losing heat for more of the day than it is gaining it. That’s oversimplifying, because the rate of heat loss depends on the current temperature, but it should give you a head start.
The phenomenon is an example of Hysteresis.
The warmth of any particular day is not only dependent on the sun’s input that day - it’s also dependent on previous states.