
Global wave discovery ends 220-year search - tejohnso
https://www.quantamagazine.org/weather-data-reveals-long-predicted-pressure-waves-20200813/
======
ChuckMcM
Laplace had an amazing mind. He connected so many dots, and everything I've
done in the last four years with respect to digital signal processing ends up
rooted in something he discovered or postulated or analyzed. Fascinating, but
not too surprising, that he shows up in the weather as well.

~~~
TheOtherHobbes
What's more amazing is that all his math was done with pen and paper - no
computer assistance of any kind. Log tables were available, but all the
analysis was done by hand. And brain.

~~~
btrettel
Most of the time people are impressed by analytical skills, it's not really
justified in my view. Those skills aren't taught as much as they used to be.
You can still pick them up, but it's mostly on your own now. (Probably still
easier than Laplace had it, though.)

Anyway, just skimming the article, it sounds like Laplace simply applied
standard normal mode analysis for the wave equation in the atmosphere. This is
rather basic stuff that you can learn in an undergraduate partial differential
equations class.

In my Master's (8 years ago), I took a class on perturbation methods and
asymptotic expansions (e.g., "method of matched asymptotic expansions"). These
are approximation methods that were very common before computers became
mainstream and can be very accurate. These methods are becoming rarer and
rarer in fluid dynamics. I think they're still used extensively in theoretical
quantum mechanics.

~~~
kardos
> These methods are becoming rarer and rarer in fluid dynamics.

Why are they becoming rarer is the question. Have all the tractable asymptotic
problems been solved?

~~~
btrettel
> Have all the tractable asymptotic problems been solved?

Definitely not. I think it's more that these approaches are _viewed_ as not
necessary as numerical approximations (implemented on a computer) are more
accurate, often easier, and allow one to consider complications that would be
impossible to handle analytically.

Though analytical methods do have major advantages. Computations are made only
for special cases. You'll need a lot of computations to see functional
dependencies clearly, for instance. If the computations are expensive (and
they often are), people are unlikely to do the parametric studies needed to
see functional dependencies clearly. Ultimately an analytical expression
contains much more information than an array of numbers.

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julienchastang
This is not really a "discovery" so much as a reaffirmation of what was
previously known. The original paper is more insightful [1]. The Quanta
magazine article is interesting but the title overstates the original
citation.

[1]
[https://journals.ametsoc.org/jas/article/77/7/2519/347483/An...](https://journals.ametsoc.org/jas/article/77/7/2519/347483/An-
Array-of-Ringing-Global-Free-Modes-Discovered)

------
kebman
Not sure if it's completely related, but I found the phenomena of the North
Atlantic Oscillation [1] to be particulary useful in predicting long-term
weather around the South of Norway. This time around, in December 2019, I
predicted a rather cold summer in Norway. I made that prediction because the
winter was particularly warm and snow-less in the South East between late 2019
and early 2020. For the most part I've been correct. Except a few heat waves
this summer has been pretty cold. But the effects of global warming persists,
and it would seem the Autumn will be pretty nice here in Oslo.

[1]:
[https://en.wikipedia.org/wiki/North_Atlantic_oscillation](https://en.wikipedia.org/wiki/North_Atlantic_oscillation)

~~~
CtrlD-me
Oslo! I'm looking for a job, there. Think it's doable without speaking
Norwegian?

~~~
laurencerowe
Quite a few tech companies in Norway have an international staff and speak
English in the office. I worked for a small Norway-based open source
consultancy for a while. We spoke English in the office as most of us were not
Norwegian and most Norwegian customers were happy to work with us in English.
I spent some time working with QT Software (then part of Nokia) and their
office was also English speaking IIRC.

------
quercusa
Is there any scientific discovery with a longer gap between prediction and
validation?

~~~
bitdizzy
Do you want to count Democritus and indivisible constituents of matter?

~~~
mehrdadn
Holy cow, he predicted _way_ more than just indivisible constituents of matter
[1]:

> The theory of Democritus held that everything is composed of "atoms", which
> are physically, but not geometrically, indivisible; that between atoms,
> there lies empty space; that atoms are indestructible, and have always been
> and always will be in motion; that there is an infinite number of atoms and
> of kinds of atoms, which differ in shape and size.

The accuracy is uncanny.

[1]
[https://en.wikipedia.org/wiki/Democritus#Atomic_hypothesis](https://en.wikipedia.org/wiki/Democritus#Atomic_hypothesis)

~~~
SAI_Peregrinus
> that there is an infinite number of atoms and of kinds of atoms

Well, that bit is wrong. Especially if you take the fundamental constituents
of what are now called atoms: 6 quarks, 6 antiquarks, 6 leptons (counting
neutrinos), 6 antileptons, 5 gauge bosons, 1 scalar boson. Only 30, possibly +
whatever dark matter and dark energy are.

~~~
mehrdadn
We don't know how many kinds of atoms there are, and infinite is pretty damn
accurate all things considered. And it's pretty disingenuous to go out of your
way to take quarks to mean what he called atoms just so you can claim he's
wrong.

~~~
thaumasiotes
Are you seriously suggesting that when Democritus referred to "uncuttable
things", he meant to describe particles that would in the future be named
after his work rather than to describe particles that were indivisible?

~~~
mehrdadn
If you genuinely find that interpretation of my statement plausible then I
don't really have anything to add.

~~~
thaumasiotes
Here's your statement:

> And it's pretty disingenuous to go out of your way to take quarks to mean
> what he called atoms just so you can claim he's wrong.

You can try to identify atoms by his description of them, in which case you'd
have to choose fundamental particles. But you've already explicitly chosen to
interpret Democritus' "atoms" as identical with our "atoms", despite the fact
that they do not exhibit any of the characteristics Democritus described. What
can I conclude except that you think Democritus, in the past, named his
concept after ours, in the future?

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DiffEq
A friend of mine wondered what the RATIO between the four modes of pressure
waves are. Waves are essentially a frequency (like pitch), and he was
wondering if the ratio between these “frequencies” constitute a similar ratio
between the pitches in a chord.

~~~
TheOtherHobbes
Kind of. Technically these are _spherical harmonics_ , which are the
generalisation of the harmonic series on a sphere instead of a line - also
used in quantum theory to calculate orbitals.

The math is a bit more complex than the simple harmonic series.

[https://en.wikipedia.org/wiki/Spherical_harmonics](https://en.wikipedia.org/wiki/Spherical_harmonics)

------
DiffEq
Pythagoros and Plato, while not making a direct proposal like Laplace, had
some similar intuitions.

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jacquesm
What a great discovery. Is this going to have some kind of impact on weather
models?

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sytse
I thought for a second it was related to the recent '26-Second Pulse' XKCD
[https://xkcd.com/2344/](https://xkcd.com/2344/) but that is about seismic
waves while this is about atmospheric pressure.

