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Some Scientific Problems (Geophysics)
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Mick Harper
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I see. So neither of you think that evaporative forces are strong enough to promote anything like saturation even though I have presented you with a scenario which (I think it fair to say) anybody else, with or without scientific training and presented with the final scenario at the start, would have considered a shoe-in for producing saturation.

I have tried to come up with an extreme enough example but failed so unless you can come up with a box which does lead to saturated air (and presumably there must be one if 'saturated air' has any meaning in the real world) then I will have to leave it there.

Thanks for your ... um ... co-operation.
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Brian Ambrose



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You can have your saturated air if you want it - you just need a high enough ambient temperature. Then, you'll have a mix of saturated and not quite so saturated air as the heat source moves around. And I did agree that a high water surface area ratio to air volume ought to increase the humidity since the surface is heated from above. You just won't get 100% saturated air 100% of the time due to the moving heat source (unless it is so warm that it has become a steam room). Is that any consolation?
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Mick Harper
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You can have your saturated air if you want it - you just need a high enough ambient temperature.

No, Brian, I want you to choose the inputs. Just tell me what kind of crazy box I will need to achieve near-saturation given what you believe are the real world inputs.

Please say if you are conceding that my own crazy box will achieve near-saturation given your chosen real-world inputs.
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Brian Ambrose



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You have 10,000 m^2 of water surface area (how deep it is is not very relevant for this purpose). If what we have assumed so far is correct, then as the volume of air above that surface decreases, the humidity ought to increase overall, for any given ambient temperature. If your box has 10mm of air, then presumably the air will be quite saturated overall. That's what you need, isn't it?
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Mick Harper
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Phew, talk about herding just one cat. Now waiting for Chad to climb aboard and we can reach Denoumentsville.
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Chad


In: Ramsbottom
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Chad wrote:
O.k. At this stage, under these conditions your box has reached the point where the air cannot take on any more moisture.

Remember when I wrote the above?

It was my opinion on the state of play in box 1 after a billennium of stable temperature and pressure... And when the air cannot take on any more moisture it has reached saturation.

The problem seems to lie in your understanding of what saturation actually is.

It is when the air has reached 100% relative humidity... not to be confused with absolute humidity (which is a measure of total water content in a given volume of air regardless of temperature and pressure).

Air, as Brian keeps telling you, is able to take on varying amounts of moisture (per unit volume) proportional to its temperature. This proportionality is non linear and the hotter the air becomes, the steeper the curve of moisture holding capacity becomes.

Box 1, if left to stabilise for another billennium, at a much lower temperature (even frozen) will once again contain air at 100% relative humidity (ie saturation) but its total moisture content will have dropped. Likewise if you increase the temperature for another stable billenium the air will again be at 100% rh, but this time it will hold rather more moisture.

You can tell when air has reached saturation (100% rh) because any slight reduction in temperature, will cause the moisture in the air to start to condense. This is called the Dew Point... and when the Dew Point temperature is equal to the ambient air temperature then saturation has been achieved and relative humidity is at 100%.
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Mick Harper
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Enough of the double-talk, Chad, as you say, I don't know enough science to follow all this. It's what makes me great. I am not bowed down by detail like you pygmies. Do you accept that, given your own real world inputs, that the air in Box Three will be nothing like the atmosphere we have today? That it will be much, much more moist, humid, saturated, whatever you want to call it?
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Chad


In: Ramsbottom
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Mick Harper wrote:
Do you accept that, given your own real world inputs, that the air in Box Three will be nothing like the atmosphere we have today? That it will be much, much more moist, humid, saturated, whatever you want to call it?

Yes... but then the real world does not possess the restrictions applied to Box Three (such as a three foot capped atmosphere).
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Chad


In: Ramsbottom
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If you removed the real world inputs from Box Three, so that it only differed from Box One in the depth of its atmosphere, then after its billion year stabilisation the relative humidity of its air would be the same as Box One (100% rh).

The only reason it becomes more moist after adding the real world inputs, is that they create currents and turbulence and importantly sea spray. It is the water droplets from the sea spray (just above the surface) that increases the airborne moisture... nowt to do with evaporation.
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Mick Harper
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So, we can now at last agree on the following:
1. Our understanding of evaporation and condensation is derived from laboratory observations from which we 'scale up' to the real world
2. Both the earth and the boxes are closed systems.
3. When Box 2 (lots of air relative to the water surface) is exposed to 'real world conditions' it mimics the real world ie not much water vapour in the atmosphere.
4. When Box 3 (not much air relative to the water surface) is exposed to 'real world conditions' it is saturated or near-saturated ie not at all like real world conditions.

So it only remains to 'scale up' our experiment to the real world. The ocean is roughly 20,000 miles across and the atmosphere (being highly generous) is 200 miles high. This is the exact scale-up of a 100 metre cubic box with one metre of air at the top. (As Brian pointed out, the water depth is irrelevant.) So the real world is a scaled up version of Box Three.

Clearly the real world atmposphere is nothing like the air at the top of Box Three so it follows that either
1. Our understanding of evaporation and condensation is fundamentally flawed and/or
2. It is highly dangerous to use laboratory-derived theories when scaling up to the real world.
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Chad


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Or...

3) The conclusion you draw from the experiments are fundamentally flawed.
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Brian Ambrose



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Clearly the real world atmposphere is nothing like the air at the top of Box Three


If you recall, a 1 metre gap didn't impress me, my guess was for a 10mm gap in order to be satchworthy. In which case, there's nothing to explain.
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Chad


In: Ramsbottom
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So the real world is a scaled up version of Box Three.

No, you cannot scale up the sea spray to affect the entire atmosphere... it only rises a few meters above sea level.
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Chad


In: Ramsbottom
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...it is saturated or near-saturated ie not at all like real world conditions.

Can tell you don't live in Manchester.
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Mick Harper
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I give up on the both of you. Irrespective of the validity of my 'experiment' it introduced you to a wholly new idea: that the atmosphere is but a skin on the ocean as opposed to how we normally experience the atmosphere which is as a 'very high, cathedral-like ceiling'. Yes, I know you are both going to say you always knew that. That's the way radical new ideas are incorporated into the brain.

Thank you for your assistance.
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