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Venus Atmosphere Puzzle, one man's struggle with atmospheric physics
qraal
post Jun 5 2006, 12:15 PM
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Hi All

This might seem like a really dumb question, but what's the mass of the Cytherean atmosphere per unit area?

At first pass I thought it was easy - same as for an isothermal atmosphere, Po/g, where Po is surface pressure and g is surface gravity. Simple. Except Venus doesn't come close to approximating an isothermal atmosphere. From a graph in Mark Bullock's PhD thesis (Hi Mark if you're visiting) I pulled the figures for Po and To as 92 bar and 735 K, while the left-side of the temperature curve was 250 K at 0.1 bar and 63 km. At about 210 K the temperature drop with altitude stops, then slowly rises into the Cytherean stratosphere.

Ok. My atmospheric physics is pretty limited - I 'modelled' that lapse rate pressure curve as a power law:

P/Po = (T/To)^n

and likewise for density, d/do = (T/To)^n.

Temperature, T, as a function of altitude, Z, I computed as T(Z) = To*(1-Z/(n.Zo)).

Zo = (k.T/m.g), where k is Boltzmann's constant and m is the molecular mass of the atmosphere.

These equations I then integrated between 210 K and 0.033 bar, 70 km, and 735 K and 92 bar, zero altitude.

The resulting equation is m = (n/(n+1))*(do.Zo)*(1 - (T/To))^(n+1) - a bit of simple algebra and the Gas equation shows that do.Zo = Po/g.

Thus the mass is lower than for a simple isothermal atmosphere by roughly (n/(n+1)). In this case n = 6.33, higher than the dry adiabat for CO2 which gives n = 4.45.

Now an adiabatic or polytropic atmosphere is an idealisation, but it seems odd to me that whenever Venus' atmospheric mass is discussed people always use the higher isothermal value. Have I missed something important in the physics, or is Venus's atmospheric mass just 86.4% of the usually quoted value?
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Guest_DonPMitchell_*
post Jul 2 2006, 05:56 PM
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The U of Arizona books are essential. There are actually two Venus books, and you want them both (Venus and Venus II). Also check out their Mars book.

There have been many descent probes on Venus. The first really detailed information came from Venera-9 and 10 in 1975, which had nephelometers, spetrometers, and various other instruments. The three-layer cloud structure was discovered then, as well as the first photos of the surface.

Venera-11, 12 and the Pioneer probes arrived in 1978. The Venera probes contained more sophisticated spectrometers than the 1975 versions, and also mass spectrometers, gas chromatography and x-ray fluorescence spectrometers. The latter provided the first real data on the composition of the cloud material, including the discovery of Iron Chloride as a component. The PV large probe had a particle-size device which provided unique data. There has been much debate about the PV results, which some believe show a distinct large particle size that may be crystals -- the so-called mode 3 controversy.

Venera descent probes relayed data through the high-gain connection of the main spacecraft, so they were able to send almost 100 times as much data as the Pioneer probes, including large numbers of mass spectra and optical spectra as they descended.

The last word has been from the Vega descent probes. They were particularly geared to study the clouds and try to answer questions raised by the Pioneer particle-size spectrometer. Two different particle analyzers were on the Vega probes, as well as a more sophisticated gas chromatography experiment, which discovered the profile of chlorine, sulphur and phosphorus abundance as a function of altitude. The clouds are a lot more complex than just sulphuric acid droplets, particularly the lower layers.

The big names in Venusian atmospheric chemistry are Vladimir Krasnopolsky, the late Vasily Moroz and Larry Esposito. They have a joint paper in Venus II, and Krasnopolsky has a good book on the chemistry of Mars and Venus.
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qraal
post Jul 2 2006, 11:47 PM
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Hi Don

Hey thanks for the insights - Venus is truly weird. Would be dull if it was easy.

Your webpages on the Russian Venus efforts are amazing too.

What do you think the 'crystals' in the atmosphere might be?

Adam

QUOTE (DonPMitchell @ Jul 3 2006, 05:56 AM) *
The U of Arizona books are essential. There are actually two Venus books, and you want them both (Venus and Venus II). Also check out their Mars book.

There have been many descent probes on Venus. The first really detailed information came from Venera-9 and 10 in 1975, which had nephelometers, spetrometers, and various other instruments. The three-layer cloud structure was discovered then, as well as the first photos of the surface.

Venera-11, 12 and the Pioneer probes arrived in 1978. The Venera probes contained more sophisticated spectrometers than the 1975 versions, and also mass spectrometers, gas chromatography and x-ray fluorescence spectrometers. The latter provided the first real data on the composition of the cloud material, including the discovery of Iron Chloride as a component. The PV large probe had a particle-size device which provided unique data. There has been much debate about the PV results, which some believe show a distinct large particle size that may be crystals -- the so-called mode 3 controversy.

Venera descent probes relayed data through the high-gain connection of the main spacecraft, so they were able to send almost 100 times as much data as the Pioneer probes, including large numbers of mass spectra and optical spectra as they descended.

The last word has been from the Vega descent probes. They were particularly geared to study the clouds and try to answer questions raised by the Pioneer particle-size spectrometer. Two different particle analyzers were on the Vega probes, as well as a more sophisticated gas chromatography experiment, which discovered the profile of chlorine, sulphur and phosphorus abundance as a function of altitude. The clouds are a lot more complex than just sulphuric acid droplets, particularly the lower layers.

The big names in Venusian atmospheric chemistry are Vladimir Krasnopolsky, the late Vasily Moroz and Larry Esposito. They have a joint paper in Venus II, and Krasnopolsky has a good book on the chemistry of Mars and Venus.
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Posts in this topic
- qraal   Venus Atmosphere Puzzle   Jun 5 2006, 12:15 PM
- - remcook   QUOTE do.Zo = Po/g This is the equation for hydro...   Jun 5 2006, 02:15 PM
|- - qraal   Hi rem That's exactly what I did and I still ...   Jun 5 2006, 11:45 PM
|- - The Messenger   QUOTE (qraal @ Jun 5 2006, 05:45 PM) That...   Jun 9 2006, 01:57 PM
- - ngunn   In an atmosphere in which temperature decreases ra...   Jun 6 2006, 11:37 AM
|- - qraal   Hi ngunn Thanks for the reply. You know I wondere...   Jun 7 2006, 12:14 PM
- - ngunn   Well you've done the detailed calculations, no...   Jun 7 2006, 12:46 PM
|- - qraal   Hi ngunn I've read it before, but replicated ...   Jun 9 2006, 12:43 PM
- - Phil Stooke   There's some great Venus atmosphere stuff (and...   Jun 7 2006, 01:50 PM
|- - DonPMitchell   QUOTE (Phil Stooke @ Jun 7 2006, 06:50 AM...   Jun 7 2006, 08:33 PM
- - ngunn   Very interesting, and I follow the reasoning you g...   Jun 9 2006, 12:57 PM
- - ngunn   Hi graal. I think that the messenger's messag...   Jun 10 2006, 10:39 AM
|- - qraal   Hi Nigel Ok. Let's try again. Everything you...   Jun 10 2006, 12:34 PM
- - ngunn   Fine. I agree the adiabatic model is probably a b...   Jun 12 2006, 11:23 AM
|- - The Messenger   QUOTE (ngunn @ Jun 12 2006, 05:23 AM) Fin...   Jun 12 2006, 08:56 PM
- - ngunn   Hi Messenger. You found my post confusing??!...   Jun 14 2006, 09:04 AM
- - remcook   just a note: Titan's temperature does vary sig...   Jun 14 2006, 11:36 AM
- - qraal   Hi All Well I decided to do a numerical experimen...   Jun 23 2006, 12:42 PM
|- - The Messenger   [quote name='qraal' date='Jun 23 2006,...   Jun 23 2006, 04:44 PM
- - qraal   Hi again And the average temperature is 630 K. H...   Jun 23 2006, 01:11 PM
|- - ngunn   QUOTE (qraal @ Jun 23 2006, 02:11 PM) Hmm...   Jun 23 2006, 01:51 PM
- - qraal   Hi Messenger & ngunn Hey thanks for the nice ...   Jun 25 2006, 12:50 AM
- - RNeuhaus   Venus' Double Vortex Confirmed in New Animatio...   Jun 27 2006, 10:21 PM
|- - DonPMitchell   At last, some pictures from VEX. These are fascin...   Jun 28 2006, 01:33 AM
||- - qraal   Thanks Don Man that's so bizarre. Venus is a...   Jun 28 2006, 10:21 AM
||- - qraal   Hi All Updated the gravity - now it's a linea...   Jun 30 2006, 02:11 PM
|- - JRehling   QUOTE (RNeuhaus @ Jun 27 2006, 03:21 PM) ...   Jul 3 2006, 10:02 PM
- - edstrick   The soviet venus descent probes measured light lev...   Jul 1 2006, 07:43 AM
- - qraal   Hi ed Thanks for the heads up on that reference, ...   Jul 1 2006, 12:38 PM
- - edstrick   The Univ of Arizona has had a method of producing ...   Jul 2 2006, 08:41 AM
- - DonPMitchell   The U of Arizona books are essential. There are a...   Jul 2 2006, 05:56 PM
|- - qraal   Hi Don Hey thanks for the insights - Venus is tru...   Jul 2 2006, 11:47 PM
|- - rlorenz   QUOTE (DonPMitchell @ Jul 2 2006, 01:56 P...   Jul 13 2007, 12:08 PM
- - DonPMitchell   That is a mystery. Many believe there are no crys...   Jul 3 2006, 01:01 AM
|- - qraal   Hi Don The exobiological theory is the most excit...   Jul 3 2006, 08:52 AM
- - edstrick   The Pioneer Large Probe Cloud Particle Size Spectr...   Jul 3 2006, 09:18 AM
- - DonPMitchell   Vega-1 and Vega-2 performed similar experiments. ...   Jul 3 2006, 04:16 PM
|- - qraal   Thanks Don & Ed More data to cram into my bra...   Jul 4 2006, 01:16 AM
- - DonPMitchell   Planetary circulation is fascinating. Rotating pa...   Jul 4 2006, 01:26 AM
|- - Bob Shaw   QUOTE (DonPMitchell @ Jul 4 2006, 02:26 A...   Jul 4 2006, 02:31 PM
- - MichaelT   QUOTE (qraal @ Jun 5 2006, 12:15 PM) Hi A...   Jul 4 2006, 09:25 AM
|- - ngunn   QUOTE (MichaelT @ Jul 4 2006, 10:25 AM) I...   Jul 4 2006, 03:51 PM
|- - MichaelT   QUOTE (ngunn @ Jul 4 2006, 03:51 PM) meas...   Jul 4 2006, 04:40 PM
|- - The Messenger   QUOTE (MichaelT @ Jul 4 2006, 10:40 AM) O...   Jul 4 2006, 07:22 PM
- - edstrick   I'd forgotten the instruments on the Vega prob...   Jul 4 2006, 10:17 AM
- - ngunn   Which is what I still don't understand (or bel...   Jul 5 2006, 09:19 AM
|- - qraal   Hi ngunn For the first 200 km of altitude Venus...   Jul 5 2006, 11:18 AM
- - ngunn   Ah! qraal with a Q - my apologies. It's th...   Jul 5 2006, 01:08 PM
- - qraal   Hi ngunn & MichaelT As you might've guess...   Jul 5 2006, 10:32 PM
|- - MichaelT   QUOTE (qraal @ Jul 5 2006, 10:32 PM) If s...   Jul 6 2006, 06:27 PM
|- - qraal   Hi Michael There's quite a lot of literature,...   Jul 10 2006, 07:56 AM
- - DonPMitchell   You're looking at Mark Bullock's thesis I ...   Jul 5 2006, 10:49 PM
- - ljk4-1   Venus Atmosphere Profile from a Maximum Entropy Pr...   Sep 26 2006, 02:36 PM
|- - rlorenz   QUOTE (ljk4-1 @ Sep 26 2006, 10:36 A...   Jul 13 2007, 12:16 PM
- - qraal   Hi All I haven't bothered with this for some ...   Jul 12 2007, 11:05 PM
- - edstrick   "....Sadly, it isnt cheap..." I'd sa...   Jul 14 2007, 06:03 AM


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