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---------- Forwarded message ----------
From: John Denker <email@example.com>
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
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.