In article ,
"Ed Huntress" wrote:

"Joseph Gwinn" wrote in message
...
In article ,
"Ed Huntress" wrote:

"Joseph Gwinn" wrote in message
...
In article ,
"Ed Huntress" wrote:

"Joseph Gwinn" wrote in message
...
In article ,
"Ed Huntress" wrote:

[snip]

You're talking about one measurement path, a Great Circle, which
may
or
may
not cross numerous currents, the initiation site for El Nino, and
so
on.
From that you're trying to draw a conclusion about global warming.
You
don't
know if the pattern between here and NZ is pro-cyclical or
counter-cyclical
to the earth's temperature as a whole. You are talking about a
measurement
taken over a short span of years, while the data being looked at by
serious
scientists is data from decades at least, and hundreds of years in
some
cases.

Well, I don't have a dog in the debate from which this is taken, but
I
will add
that it is not impossible to disentangle all those things. What is
done
is the acoustic equivalent of computerized tomography.

Here is a random article dredged up by google:
http://jjap.ipap.jp/link?JJAP/40/5446/.

Joe Gwinn

Joe, I'm going to skip the article, because there are 2,000 or 3,000
that
I'd have to read first.

Not if the intent is to understand the method.

Hey, Joe, I got curious and took a look at it. What in the hell are you
talking about here? Of COURSE temperature differentials result in sound
velocity differentials. That wasn't the question. Nor are statistical
sampling methods part of the question.

Nor was it the point.


The question is, what is the effect of all of the variables upon ocean
temperature, current temperatures and paths, and their cyclical or
countercyclical relation to worldwide global warming? What's causing
warming
or cooling along that linear path, and how does it relate to the overall
effect?

As I said, this allows one to measure the changes. Explaining them is
quite
another matter.

Well, we know that there are methods to measure the changes in ocean
temperature. There is only one significant question here, which is what does
it really tell us about overall warming? Dan's original point was that if
the guy he knows who is doing this work tells him there is global warming,
he'll believe it. To which my response is, I can't see how.

I have not talked to Dan's friend, but I would guess that the friend is looking
to see if the average temperature of and/or total heat energy within the deep
ocean water mass has in fact increased, and if so by how much. This can be
accomplished by a direct measurement, without understanding why the temperature
changed.


The article doesn't touch upon that. What it DOES do is explain a method
for
measuring temperature with the velocity proxy. They've been able to do
that
for 100 years, by my guess. This is just a quick and simple method, as
the
article's title describes.

I don't think they knew of this method 100 years ago, but it doesn't
matter, as
the method is quite impractical without computers. Now it's easy.

Well, they probably knew about velocities of sound in water in relation to
the water's temperature. Maybe they could measure it in the lab.

Yes, they knew this 100 years ago.


What Dan is
talking about is measuring it across oceans. It may well be possible to a
high degree of accuracy. And it very well may tell you all kinds of useful
things about the relationships of ocean temperatures in certain regions to
weather. It probably also will tell you about a *mean* temperature trend
along a specific Great Circle line.

Measuring across oceans is precisely what is done. And, acoustic computerized
tomography gives you the voxel-by-voxel temperature of the ocean, not just the
mean temperature of a great-circle path.

The method resembles that used with X-rays (in CT scanners), where the X-ray
attenuation of a very large number of independent paths and directions is
combined mathematically to yield the 2D attenuation function (which we see as
the image).

Circling back to acoustics, what is measured is the transit times along a large
number of paths through the ocean of interest. These transit-time measurements
are combined to compute the speed of sound in each and every voxel, yielding the
speed image. From this (and independent salinity measurements) one can compute
temperature.


But the time span is too short to address the kinds of temperature trends
that are significant to the questions about global warming, and, as we've
now discussed ad nauseum, it doesn't address whether temperatures along that
particular line are in direct, or inverse relation to trends at the largest
scale.

Yes, but what's the point? Of course the Vikings didn't record such data.

But the data can help answer the question of how much thermal energy is stored
in the deep ocean, and how quickly it gets there. These are big issues in the
climate models, and measured data will help settle the arguments about which
approach is correct.


Ocean currents change their paths with changes in climate. We may be seeing
it now with the Gulf Stream; it's moved within our lifetimes, as any old
offshore fisherman can confirm. And that's only one of the variables.

True enough, but the intent is to measure heat storage in the deep ocean.


Joe Gwinn