Here in Washington, D.C. we made it all the way to Christmas with relatively mild temperatures and no snow.
But, just as every other year, this is not to last. Just as the days get longer, temperatures start to drop, and stay there for months.
My question is, why does this happen, if it’s the earth’s tilt that determines the seasons? Shouldn’t it on average get warmer past the solstice?
I’ve heard answers like “momentum” but that doesn’t seem to answer much. My theory is increased albedo from the snow in more northern climes. The sun has to struggle up to a much longer day before it can overcome this. I have zero evidence here, though. Does anyone have the defininitive answer?
The reason is that heat is stored in the ocean, lakes, and the earth itself. Once the ground and lakes freeze, it takes a large amount of energy to melt them. This is why the seasons lag the astronomical seasons. The same is true in the fall-while the sunlite hours decline (and the angle of the sun becomes more oblique)it still stays warm, because of the heat stored in the ground. (also why cities are warmer than the country-more heat storage in blactop paving,buildings, etc.)
Ok, fair enough. But the ground around here doesn’t begin to freeze until after the solstice.
If the cold we are getting is from areas where this has already occurred, shouldn’t they be slightly warmer due to the heat energy gained from us? Shouldn’t, on average, it still be getting warmer?
But since I have no way of checking this (it may in fact be the case), I’ll stick with it as the definitive answer until I can check to see whether the amount of sunlight reflected off of snow makes any difference whatsoever.
The only reason I guessed albedo (rather then the delay in reversing already frozen ground) was that temperatures all over the northern hemisphere seem to continue dropping after the solstice, including ground and water temperatures. You’d think all the solar energy would be going SOMEWHERE.
Ok, fair enough. But the ground around here doesn’t begin to freeze until after the solstice.
If the cold we are getting is from areas where this has already occurred, shouldn’t they be slightly warmer due to the heat energy gained from us? Shouldn’t, on average, it still be getting warmer?
But since I have no way of checking this (it may in fact be the case), I’ll stick with it as the definitive answer until I can check to see whether the amount of sunlight reflected off of snow makes any difference whatsoever.
The only reason I guessed albedo (rather then the delay in reversing already frozen ground) was that temperatures all over the northern hemisphere seem to continue dropping after the solstice, including ground and water temperatures. You’d think all the solar energy would be going SOMEWHERE.
Let us consider the ‘energy balance model’. A given spot on the Earth’s surface loses energy all the time by radiating. The amount of energy it loses depends on its temperature, but not a lot, and we can assume that it it’s constant every minute and every day.
The amount of energy it receives from insolation depends on a number of factors, the most significant being the length of the day and the angle, both of which depend on the calendar date. The surface albedo (the percentage of solar energy reflected back into space) and the atmosphere (clouds, haze, etc) are much less important. Besides, I doubt you have that much snow/ice in DC right now.
There’s no insolation at night, so for further simplicity let us plot the energy balance on a calendar day as a sine-like curve. Its lowest point is Dec 22 - we lose the most energy. After that day, the balance is still negative, but the insolation is increasing, so on the average it’s getting colder slower.
Note also that the ocean can radiate and still keep warm or absorb solar energy and keep cold. It takes more energy to heat up ocean than a comparable amount of dry land. That’s why, e.g., in Arizona it can be very hot during the day and then very cold soon after the sunset, which doesn’t happen near the ocean coast.
Ok, I can accept it getting colder more slowly.
That makes sense. In other words, it’s not until the length of day passes over some critical balance where the amount of heat lost when the sun isn’t around is exceeded by the amount of heat gained when it is that things stop getting colder, and start getting warmer. It’s fairly obvious that this wouldn’t be at the solstice.
Um. Nope.
Cool word though. You use it on co-workers a lot?
Sorry, it’s not a lagging behind, but the fact that it will start getting colder between equinoxes roughly, not solstices.
Which makes sense if you think about it.
It’s a big world, and its weather is a complex interaction between many forces. For this reason, cause and effect can be separated by days, weeks, months, etc. Like I said, hysteresis.
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