Rain1

While watching the weather on TV, the announcer tells us about a huge storm approaching the coast. It would be quite usual to hear him say something like this. " There is a massive buildup of cloud, and the mercury is plummeting."

What does this really mean ?

There is a huge increase in the weight of the atmosphere as evidenced by the clouds.
AND
There is a huge decrease in the weight of the atmosphere as evidenced by the Barometer

This appears to be a Contradiction in Terms, or perhaps an "Oxygenmoron"

Which is correct?. Our interpretation of the clouds, or our interpretation of the barometer.

There appear to be 3 stages to the formation and distribution of rain, and none seem to be completely understood, although strong opinions are generally expressed.

The first is the absorption of water vapor into the air and it's elevation. The best theory, and the one that I would agree with, is that the atomic weights of the components of dry air are greater than those of air with water vapor. That is, humid air will weigh less than dry air for the same volume, and will therefore rise. This seems to explain how the moisture gets up into the atmosphere.

Secondly, as the humid air rises it moves into progressively cooler areas, and lower pressures, and therefore begins to condense. As it condenses heat is released and the following moist air is warmed a little and can rise a little further, where it too will condense. This process continues until the prevailing conditions leave us with a large cloud mass. The real confusion begins here. What keeps the clouds up there ?. The laws of gravity say that they must fall. Most answers to this suggest that updrafts keep the clouds up. Updrafts imply heat to cause them, but cloud formations can stay put, sometimes through several day/night cycles, from horizon to horizon, as far as the eye can see, even when the temperature plummets, when downdrafts are more likely to occur.

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