I was pondering Clouds and wondering “If they are droplets, why do folks talk about water VAPOR?” when I then pondered, if they are water droplets, why don’t they fall?
Found a very good page that explains why clouds don’t fall, so I’ll not try to re-write it. The short answer is “they do”. Rain, when droplets are very big, and “very slowly” when droplets are small. Sometimes, as very small droplets, they fall so slowly that upward air currents will carry them up faster than they fall. Then the clouds are “falling up”…
It all comes down to Stokes Law. Small stuff falls slower.
Skipping over the math part (that you can get at the link):
Clouds can hold an enormous amount of water. When this water falls as rain it clearly has a significant mass so why don’t clouds fall? In fact, the small water droplets that make up clouds do fall slowly. However, the drag force of the air dominates over the gravitational force for small particles. The drag force increases as the size of an object decreases. The force needed to move a sphere through a viscous medium is given by Stokes’s law,
A water droplet with a 10 nm radius falls at 12 nm/s in air. It would take 2.6 years for this droplet to fall one meter. It is only when the small droplets begin to coalesce into larger droplets that they fall with significant speed.
In some sense, the inverse effect to rain is the rising of bubbles in beer. Bubbles are lighter than the surrounding liquid so gravity pushes them up. They rise with a constant velocity which is described by Stokes law. If you are the type that carefully observes your beer, you will have noticed that sometimes the bubbles move down. This is because of the circulation of liquid in the beer glass. The rising bubbles in the center of the glass drag some liquid along with them. After this liquid reaches the top of the glass, it returns to the bottom along the sides of the glass. This downward flow can drag bubbles, especially small bubbles, downwards against the force of gravity.
In a similar manner, small rain drops can be pull up by air currents against the force of gravity.
So that’s why, when a cloud starts to form, it can continue to rise.
Water vapor is lighter than air. Hot humid air rises. As the humidity condenses to make a cloud, it continues to lift the cloud (inertia in part, heat of vaporization being released in condensation for another)
Eventually the droplets get big enough to fall fast enough to beat the uplift ‘from other causes’ and we get rain. Sometimes heavy rain. Falling from that rising developing thunderhead.
IMHO, this, too, argues that the best way to detect any increase or decrease of ‘warming’ would be just to look at the height of the tropopause. If more heat is arriving, it ought to raise the tropopause. If less heat, lower. ALL the heat is dumped, it’s just a question of how fast and is the variation enough to see it in tropopause hight and / or storm frequency.
Basically, to see the heat leaving, look for “clouds falling up”… and measure them.
A corollary to this ought to be that places like Alaska, that have thunderstorms only during the peak of summer, ought to be decent recorders of heat flux variation. Number, frequency, and dates of onset and ending of thunderstorms all ought to ‘give a clue’ about relative heat flows over time. Height of tropopause and rate of change seasonally ought to be useful too.
Now I wonder if we have any of that data for the last 100 years…
And a second corollary is that if Alaska only has thunderstorms in a few summer months, that indicates the heat flux level, or threshold, that CAUSES thunderstorms to dump the excess heat. The “lower bound” for convective cell acceleration to dump the added heat. (At the other extreme, in somewhere like the Mojave Desert that has sporadic thunderstorms, the tendency to END in the hottest parts of summer would indicate when heat makes water so scarce as to end the cycle. When the Spherical Heat Pipe Earth is so hot that the working fluid does not fall as rain and recycle, stopping the heat pump. (This is more speculative as deserts are largely the result of rain being stopped at earlier mountains, not a thermal limit per-se, so you would need to allow for that and adjust, if possible, to see the result. Perhaps a humidity / temperature nomogram).
The inevitable conclusion of those two speculations would be that were “Global Warming” real, it would have has it’s net result a northward migration of thunderstorm size and frequency… and not much else. The heat would still leave daily; it would just do so in slightly different locations. (And the ocean over the equatorial zone would evaporate more water to drive the tropical belt of thunderstorms even faster).
IMHO, you also need to allow for longer term dis-equilibrium states where heat IS stored in the ocean, only to be dumped later as lots of excess rain. That whole PDO / AMO cycle thing. So the Sun goes more active, we get more UV, it ends up as stratospheric heat and so, slower air cycling. The added sun slowly warms the ocean. Time passes, the sun takes a nap, and we get a colder ‘cold pole’ to the ‘heat pipe earth’ as the UV drops off; with a hotter ocean left over (as heating excess just ended). The net result OUGHT to be massive rains, as the ocean dumps heat via water cycling to the tropopause in excess storm formation.
And that is what we’ve seen the last couple of years. Added rains during a turn to ‘cold phase’ actions…
If it really is “all about the convection”, then looking for size, frequency, and location of convective cells and records of precipitation ought to tell us when there were periods of greater and lesser heat flow into the system. When the sun was quiet and when it was active. That, in turn, ought to tell us if anything ‘unexpected’ is happening.
IMHO, the unexpected IS happening. The sun went quiet and we’ve got rain. Lots of it. Just as we’d predict from the preceding solar heated ocean and excess warming from the prior higher solar activity. That precipitation tells us the first derivative of heat change… A very useful thing… and right how it is saying “cold stratosphere, warm ocean, lots of rain establishing new equilibrium state”.
The preceding times of reduced rain also assert that when the sun was more active, IT was causing the warmer weather.
I think you can learn a lot from watching clouds falling up ;-)