Lucia’s Confusion About Convection (via


The density of water vapor, moist are and dry air at the ‘continuum mechanics’ level are what they are and these have been measured. The density of all water vapor, most air and dry air are well known based on empirical data. That is: experiments.

Jim McGinn:
The issue is weight (not relative density) of moist air vs. dry air. Relative weight between moist/dry air has never been measured. So the notion that storms are powered by buoyancy (of moist air) is but a theoretical construct. There is zero empirical data on this question.

The heart of the confusion, it seems is that when they refer to “density” they are actually referring to RELATIVE density of H2O in a volume of air. Don’t be confused by this obscurantism. And, if you think you have empirical/measured data that resolves the issue then, by all means, present it. Nobody (especially not me) is interested in debating your imagination.

The debate over dimers may matter in the debate over radiative properties of water in the atmosphere, but it just isn’t important to our understanding of density of water vapor.

Jim McGinn:
You obviously haven’t a clue what you are talking about. Buoyancy is a central concept to storm theory. Do some research before you respond, or if you know something the rest of the world has yet to figure out, please tell us your special secret.

Sure in principle if the concentration of dimers was very, very large, then the density of water vapor might be very large. But it is a fact that we happen to know all of the density of water better than we know the specific configuration of molecules.

Jim McGinn
Knowing the RELATIVE density doesn’t translate into knowing the weight of different bodies of air. Remember, you imagination is not evidence.  You are making the same dumbass mistake that meteorologists make–assuming that H2O is monomolecular at ambient temperatures.  So your speculation is just as worthless as is theirs.

More refined measurements were taken later– but we do know the density of water as vapor,

Jim McGinn:
You/we know the RELATIVE DENSITY. You/we do not know the relative weight/volume of dry air to moist air. THESE ARE TWO VERY DIFFERENT THINGS/ISSUES.

liquid or ice. Novel theories about molecular composition of water as vapor need to be consistent with the long known and easily measurable densities of liquid water and water vapor. We don’t need to feel the slightest doubt about the density of water merely because someone dreams up some theory about ‘dimers’ of water.

Jim McGinn:
Repeating the same misconception over and over again doesn’t make it more true/valid. It doesn’t matter how many times you babble about RELATIVE density it doesn’t tell us what we need to know in regards to the convection hypothesis. Like many before you, you have transposed the concepts of density/mass with the concept of relative density. And, thusly, you are slipping on the same conceptual banana peel that people have been slipping on for over a hundred years now. If you have empirical data that indicates moist air is lighter than dry air–which you obviously do not have–then please enlighten us!

As I told Chuck Doswell: Stop telling us what you know, like a priest, and start telling us how you know it, like a scientist.

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