Welcome Dallas Kennedy !!
Tim Thompson (tim@lithos.jpl.nasa.gov)
25 Jan 1995 19:07:49 GMT
I have distributed this post to the 3 newsgroups on which the original,
to which I am replying, was posted. I have set followups to talk.origins,
and I will not post further on this matter to any other group. Since
I do not read sci.anthropology or sci.archaeology, you will have to E-mail
(or cross post to talk.origins) anything you want me to see.
In article 168@no-names.nerdc.ufl.edu, kennedy@quark.phys.ufl.edu
(Dallas Kennedy) writes:
[From kennedy@quark.phys.ufl.edu (Dallas Kennedy)]
[Newsgroups: talk.origins,sci.anthropology,sci.archaeology]
[Subject: Re: "Sagan and Velikovsky" to appear in local book stores]
[Date: 25 Jan 1995 05:59:20 GMT]
Welcome to the the "Venus is out of Thermal Balance debate". I see you
have not been following the "debate" between myself and Ted Holden.
Needless to say, you are way off. and very wrong, as I shall now
proceed to demonstrate. However, before that, a suggestion or two.
First, check out the message I posted yesterday (talk.origins) under the
subject heading "Son of Nightmare on Ted Street". It contains very convincing
factual evidence that Venus is *NOT* out of thermal balance. Second,
check out the T.O. FAQ archive, specifically the file named "venus-young",
written by Yours Truly, which discusses the physics of Venus, and why it
cannot be a young planet, as the Velikovskian insists. Now, to business.
> The main conventional book on Venus I was thinking of, was _Venus_, published
> by U. Arizona Press in 1983 [?]. It uses the Pioneer and Venera data, but
> clearly not the Magellan data.
A good place to start. I approve.
> One item that is clear from that book is that Venus is not in thermal balance;
> that is, its heat out flux (157 W/m^2) is larger than its light in flux
> (106 W/m^2), after the albedo (0.84) is taken into account.
Wrong, on several points. First, nobody gives an albedo, for what it's
worth, of 0.84. The largest albedo reported therein is 0.80. The radiance
numbers you give are wrong too. The total outgoing power is 3.5 +/- 0.3
X 10^16 W, and the total incoming power is 3.1 +/- 0.3 X 10^16 W,
(Taylor, et al., 1980), which is translated by Schofield & Taylor, 1982,
into a mean net absorption of 132 +/- 13 W/m^2 and a mean net emission of
153 +/- 13 W/m^2. As you can see, the error bars overlap rather clearly,
which means that these data do not provide any but the most tentative
evidence of thermal imbalance, and they exclude the possibility of any
significant imbalance altogether. The albedo is an irrelevant quantity.
> The chapter
> in the book that deals with this concludes that there "cannot" be an internal
> heat source, so it just ad hoc changes the albedo to adjust the heat budget
> into balance.
Nice try, but no cigar. The author, F.W. Taylor, concluded that there
could not be a radiative imbalance because other evidence that one would
expect was not forthcoming. This fully justifies the presumption that
there is no thermal imbalance, as the radiative figures indicate anyway.
> The runaway greenhouse model of Sagan to explain Venus' high surface tempera-
> tures has a number of fatal problems. The conventional version assumes thermal
> balance. But even if there were thermal balance, the greenhouse suffers from
> these flaws: (1) no adverse thermal gradient below the cloud tops; and (2)
> almost no water vapor. (1) For the trapping of heat to occur, thermodynamics
> requires the presence of a temperature inversion to prevent the heat at the
> surface from flowing out (by diffusion or conduction). There is evidently no
> significant convection in the lower atmosphere (below the cloud tops). The
> Earth's "atmosphere" effect is based on the temperature inversion in the lower
> atmosphere. This inversion is absent in the case of Venus.
All wrong. Temperature inversions serve to prevent heat transfer by
*convection* only, they have no effect on conduction (which is not a relevent
process here anyway) or radiation. The dominant mode of heat transfer in the
lower atmosphere of Venus is radiative, and this is not affected by the absence
of a temperature inversion. Heat is trapped in the lower atmosphere because
it is radiatively opaque.
Furthermore, the absence of vertical convection, which you have been
kind enough to admit, is itself very strong evidence, perhaps the strongest
of all, that Venus *cannot* be "out of thermal balance". The reason is that,
in order for the out-of-thermal-balance argument to hold, the planet must
be heating its own atmosphere from below. If this were the case, then the
lower atmosphere would have to be vertically convective, especially when
it is so radiatively opaque. The Earth's lower atmosphere is convective,
that of Venus is not. The absence of convection precludes heating from
below, and therefore eliminates the out-of-thermal-balance argument from
contention.
> (2) The trapping
> of IR radiation requires, for full coverage of the IR spectrum, water vapor
> in addition to CO2. But Venus' atmosphere has much less water vapor than
> necessary to make the runaway greenhouse work.
This is not correct.
[ ... ]
> It won't do to claim that Venus may have had much more water vapor in the past,
> enough to establish a runaway greenhouse then. The model needs the water
> vapor (or a suitable substitute) to be there *now*, to keep the high tempera-
> ture in a steady state. The same goes for the inverse temperature gradient.
This is incorrect. There is no requirement for water to be present in
the atmosphere of Venus *now* to explain the greenhouse effect, and the
presence of a higher water concentration in the past is suggested by the
peculiar D/H ratio in the Venus atmosphere. This was all covered by Pollack,
et al., 1980, and there are several more recent papers that refine the issue
well beyond your current state of knowledge. I suggest you seek out the
library, and start reading.
> I think that the greenhouse model should have been junked after the Pioneer
> data were available (after 1979). I do not argue that an ordinary or runaway
> greenhouse effect is impossible under the right conditions, but only that
> those conditions are not present on Venus today, given the data I have seen.
> The greenhouse model is a good example of people committing to a flawed idea
> before there was much information to judge the idea and then clinging to that
> idea well after more and better information had become available that refuted
> the idea.
Well, as I have already shown the anti-greenhouse sentiment is not well
considered. The greenhouse effect works just fine. But, it is also a naieve
view of science. Scientists do not act in this politically-unified manner,
as you seem to think they do. Scientists compete just like atheletes, and
are only too happy to uncover each others mistakes, in public if possible.
If this were really an ideological issue, it would have crumbled long ago.
> There are other strange features of Venus, not related to the greenhouse, but
> worth noting. (1) The atmosphere does not have much argon (from the radio-
> active decay of potassium, I think). An old atmosphere, like the Earth's,
> should have more argon. The beta decay half-life of potassium-40 is about
> 10^9 yr.
Actually, it's about 1.2 X 10^10 years. A fully chondritic Venus would
lead to a 40Ar partial pressure of about 56 mbar. The Earth shows ~9 mbar,
and Venus shows about 2 to 3 mbar. There is clearly a connection between
the chemical composition of the planet, and it's chemical evolution, and
the Argon abundance. All of these details need to be investigated before
one simply rattles off a quick conclusion that there is something wrong
with the age of Venus because of its Argon abundance. (Lewis & Prinn, 1984)
> (2) If solar heating were the dominant heating at Venus' surface,
> one would expect the equatorial region to be hotter than the poles (like the
> Earth). However, Venus' poles have measured to have temperatures close to or
> even about equal to the equatorial temperatures. From this, I infer that
> the dominant heating at Venus' surface is not solar, but internal.
The problem is that the atmosphere of the Earth is nowhere near so
radiatively opaque as the atmosphere ov Venus. The surface of the Earth
can cool radiatively, directly to space, the surface of Venus cannot.
Also, the pole-to-equator circulation on Earth is quite wimpy compared
to the very strong superrotation of the Venus atmosphere; the thermosphere
of Venus is observed to rotate around the planet once every 4 days (Earth
days), while rotation on its axis (1 Venus day) takes about 225 Earth days.
In other words, the atmosphere of Venus convects horizontally instead of
vertically, efficiently transferring heat from the "day" side to the "night"
side, whre radiative cooling to space is more efficient. This is exactly
what thermodynamics would suggest.
> (3) Venus
> has a youthful-looking surface, not gnarled and wrinkly like the Earth's :)
How youthful? What does "youthful" mean for a planet? Standard theory
suggests that this surface, in many places, is about 500,000,000 years
old. That may sound "youthful" on a geophysical scale, but if the
solar system is 5 billion years old, thats still 10% of the life of
the solar system, and that's a significant chunk of time. It is
certainly a lot older than will do Velikovsky any good.
> How the planet science community could have kept up the greenhouse model,
> especially with no inverted temperature gradient, is bizarre. I assume it
> is by inertia or politics.
Your assumption is wrong, as is your intuition for temperature gradients.
Better luck next time, it's nice to see that Ted doesn't have to feel
lonely any more.
Obligatory References ...
[Note: JGR = "Journal of Geophysical Research"]
Lewis, J.S & R.G. Prinn
"Planets and Their Atmospheres"
Academic Press, 1984
Pollack, et al.,
"Greenhouse Models of Venus' High Surface Temperature, as Constrained
by Pioneer Venus Measurements"
JGR - Space Physics 85(A13): 8223-8231 (December 30, 1980)
Schofield, J.T & Taylor, F.W.
"Net Global Emission from the Venusian Atmosphere"
Icarus, 52(2): 245-262 (November 1982)
Taylor, F.W. et al.,
"Structure and Meteorology of the Middle Atmosphere of Venus: Infrared
Remote Sensing From the Pioneer Orbiter"
JGR - Space Physics 85(A13): 7963-8006 (December 30, 1980)
Tomasko, M.G. et al.,
"The Thermal Balance of Venus in Light of the Pioneer Venus Mission"
JGR - Space Physics 85(A13): 8187-8199 (December 30, 1980)
---
Speaking only for myself ...
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Timothy J. Thompson, Timothy.J.Thompson@jpl.nasa.gov
California Institute of Technology, Jet Propulsion Laboratory ...
Earth & Space Sciences Division, Terrestrial Science Element ...
ASTER Project Atmospheric Corrections Science Team ...
Vice President, Mount Wilson Observatory Association ...
Board of Directors, Los Angeles Astronomical Society.
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