Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

[Phys-L] Physics, seasons, and temperature.

As usual, John Denker's response is excellent and detailed (thank you for
the Vonnegut reference). I'd like to add a bit of atmospheric physics to
the question of temperatures.
Most humans are concerned about the temperature and weather conditions
where they are physically at. That means land. Our planet is 71% covered by
water. Water and soil have different thermal properties. (Hence "sea
breezes" and "land breezes" which generally switch each day in coastal
areas in response to solar warming.)
One result of this is that the oceans store a vast amount of thermal energy
and are slow to change compared to land. So the summer combination of
longer days and more direct (more concentrated) rays heats the land and
sea, but it takes a while for everything to warm up. The cold ocean is slow
to warm up and the sea breezes keep flowing that colder air over the land.
Bingo, it takes longer for the land to warm.
There are global air convection cells that respond to the seasons and move
air from over the ocean to over the land even in large scale areas like the
middle of continents. All of this takes time and that is part of the lag of
temperature change vs. sun position in the sky.

Finally, for the sake of completeness, as I alluded to above there are TWO
things that cause the seasons in mid and upper latitudes. Not just longer
days, but also more direct illumination as the Sun gets higher in the sky.


- - - -
John E. Sohl, Ph.D.
WSU Brady Presidential Distinguished Professor of Physics
Weber State University
1415 Edvalson St., Dept 2508
Ogden, UT 84408-2508

Office: TY 326
Office phone: (801) 626-7907
cell: (801) 476-0589 (Text me, I don't answer the phone if you are not in
my contacts.)

---------- Forwarded message ----------
From: John Denker <>
Date: Tue, 23 Mar 2021 19:52:37 -0700
Subject: Re: [Phys-L] definition of spring

4) Let's now focus on the case where there are four seasons,
and focus on temperate latitudes. The question then arises,
why is the temperature not a simple function of the length
of the day?

There is an interesting physics answer to that question.
It turns out that the system is overdamped. To a decent
approximation, it can be modeled as a one-pole low-pass
filter. So it is closely analogous to an RC circuit.
("The same equations have the same solutions.")
So the response (i.e. temperature) will lag the input (i.e.
day length) by 90 degrees of phase.

It's not quiiiite that simple; the coldest day is more
likely to be 75 or 80 days after the solstice (early February
in the northern hemisphere) rather than 90 days. Similarly
the hottest day is likely to be less than 90 days after the
solstice. So we are somewhat splitting the difference between
direct proportionality and 90° lag.

So there are physics reasons why winter and summer (by the
astronomical definition) will /contain/ the coldest and
hottest day.

Since temperature is not firmly locked to the solstices and
equinoxes, you could fudge the definitions of the seasons by
a week or two without much changing this consideration.