Venus Atmosphere Puzzle, one man's struggle with atmospheric physics Options

[qraal]

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?

[RNeuhaus]

Venus' Double Vortex Confirmed in New Animation

A huge "double-eye" atmospheric vortex has been confirmed to exist at the South Pole of the planet Venus.

http://www.space.com/scienceastronomy/0606...nus_vortex.html



There are two vortex in the South Pole. That is odd!!

Scientists think the vortexes are created by a combination of a natural cycling of hot air in the planet's atmosphere and high velocity, westward-blowing winds that take only four days circle the planet. It is still unclear, however, why there are two vortexes at each pole.

Rodolfo

[Guest_DonPMitchell_*]

At last, some pictures from VEX. These are fascinating.

[attachment=6431:attachment] [attachment=6432:attachment]

Here are the best previous images of the double vortex, by Pioneer Venus, and the Venera-15 IR spectrometer.

[qraal]

Thanks Don

Man that's so bizarre.

Venus is a surprising planet - not 'dead' at all, except in a restricted sense, and I'm still hanging out for sulphur munching bugs in the clouds.

There's a surprising amount of energy locked up in that 4 day rotation.

Adam

At last, some pictures from VEX. These are fascinating.

(snipped pix)

Here are the best previous images of the double vortex, by Pioneer Venus, and the Venera-15 IR spectrometer.

[qraal]

Hi All

Updated the gravity - now it's a linear approximation good out to about 200 km. Considering the quintic equations I used working out Cp(T) for N2 and CO2 the computational improvement is slight, but the mental exercise was worthwhile. Also I had made a basic error working out the enthalpy of the gas mix for each cell, so I've corrected that too. The total energy, using 0 K as the reference point, is about 588 GJ/sq.m.

Having done all that I've been trying to educate myself on cloud condensation physics and getting a headache in the process. Does anyone here know if the cloud layers have been measured in their vertical extent and optical depth? I'm pretty sure I've read some such data, but a good reference on the topic would be handy. The article I have is more theoretical than factual and gave me a few hints on how to modify the model, but now that I'm tweaking it I'm dissatisfied with a 'fudge factor' and want some real understanding.

Chilling Venus's atmosphere out, as a precursor to terraforming, was the main problem I wanted to investigate when I began this exercise, but as I've progressed the fun has come from comparing it against the data. Some very odd things would happen on a darkened Venus - CO2 snow would probably fall (and sublime on the way down) before CO2 rain did, for example. I've been imagining a scenario in which hydrogen was crashed into Venus to burn the CO2 into carbon and water, via the Bosch reaction, then wondering what condensing water would do to a surface made of carbon-deprived oxides of calcium and the like. Would a mad upheaval of the regolith ensue, rapidly forming carbonates? Kind of like 'cooking' limestone to make lime, but in reverse.

Adam