Sometimes it’s the little things… like virga and mist…
This article on WUWT per Willis and his adventure has an interesting comment in it.
Willis had mused about virga in his article:
I got to thinking about “virga” on this trip. Virga is rain that falls from clouds but evaporates before it hits the surface. I saw lots of it, and I wonder how much of it is captured by the climate models. In fact, how much of it is captured by observations? How would you even measure it when it doesn’t hit the ground? Gotta love the settled science …
I’ve had the joy of standing in virga that was making my face damp, but not my toes… Marvelous stuff. Typically raindrops that have evaporated to the point of being nearly nothing, and then it is nothing. Like cotton candy of the air.
Yet what it represents is a huge movement of heat from where it evaporated, to where it condensed, and then it is back to cycle again… How many times does that water cycle in that small part of our spherical heat pipe Earth? Nobody knows. And I do mean nobody. It isn’t measured, and as pointed out, nobody knows how to measure it. Often in the distance you will see what is clearly a thunderhead, dumping rain streaks, that end 1/2 way to the ground. Not even virga, it evaporates too high up, to cycle again.
I’ve commented about the potential for rain to act as a counter flow stripper scavenging CO2 from the air. This works due to the enormous surface area of droplets. Any Chem.E. or Mech.E. can tell you all about it.
The commenter, David Dibbell , had a different view of the droplets, and a very interesting one. I’m quoting his posting here in full, as it is worth reading twice…
Willis, thanks for your interesting and insightful posts, and may you have safe journeys. Your mention of virga prompts me to put here as a comment a post I composed a couple months ago on social media. I know it’s a bit long. It astounds me how so many otherwise capable folks – scientists or otherwise – can buy into such an obvious (to me) misconception about how the atmosphere works. I address the global warming issue as an old-school mechanical engineer who started with a slide rule.
I was in Mr. Heinrich’s geometry class in high school. Great teacher. So does geometry matter? Is it reliable?
Can geometry help us examine the “global warming” hypothesis? Let’s illustrate with a geometry exercise. It’s a long post, but please read on if you are curious and wish to consider this question from an alternative viewpoint.
About one meter (40 inches) of precipitation falls per year, averaged over the globe. This is one cubic meter of volume per square meter of surface. Raindrops are 2.5 millimeters in diameter, more or less. From geometry, one calculates that the surface area of all the raindrops in one cubic meter of water is about 2400 square meters. Hold that thought.
The global warming claim is that the lower atmosphere will heat up as concentrations of carbon dioxide and other “greenhouse gases” increase, absorbing more of the heat emitted upward by the earth’s surface. Then the warmed atmosphere emits more heat back downward, warming the surface. That’s the hypothesis. The geometry of this claim is one square meter looking up from the surface, one square meter projected downward from the atmosphere, as heat is radiated upward and downward.
But wait. The atmosphere does not actually work like that. The radiative emission and absorption of heat is in every direction from every location, not just up and down. In our illustration, as raindrops fall from cooler conditions higher up through warmer conditions down low, a huge surface area is exposed to the atmosphere for heat to be exchanged. Over a year’s time, this is 2400 square meters, on average, per square meter of earth’s surface! This geometric advantage applies to all forms of heat exchange between raindrops and the lower atmosphere: radiative, direct contact, and evaporation. The heat transfer happens rapidly as raindrops experience a stiff breeze as they fall by gravity. So just as the oceans and land surfaces are cooled by evaporation, convection, and radiative emission, so also is the lower atmosphere itself cooled, even more intensively as this geometry exercise about raindrops illustrates.
So what will an increasing concentration of carbon dioxide do? Logically, it will simply increase the effectiveness of the radiative part of the heat transfer between raindrops and the atmosphere. But will it change the temperature of the atmosphere? This is not plausible, as the fixed properties of water such as vapor pressure and latent heat of evaporation already exert such complete control over the temperature resulting from this intense interchange. Furthermore, if carbon dioxide increases the radiative effect downward near the surface, then logically the radiative effect is increased outward to space higher up where condensation occurs. Water vapor is recycled back up to condense again and form raindrops to fall back down to the surface, easily counteracting any tendency of “greenhouse gases” to change the resulting temperature down low. This happens without even implying any net change in rainfall reaching the surface. The atmosphere determines for itself how much of each raindrop makes it to the surface. We only measure the remainder. We don’t measure what doesn’t reach the surface, therefore it cannot have been modeled accurately enough for computers to tell us anything useful about it. But we can grasp what must be happening as we observe the rainfall and apply the geometry and the properties of water to this question.
So here’s the bottom line of this illustration: Some say “Dangerous carbon pollution!” “Climate catastrophe!”. But in reality, the atmosphere knows exactly what to do to control its own temperature, and will do it reliably using water as the vehicle with an overwhelming advantage in surface area. Geometry rules! Thank you Mr. Heinrich.
In highschool, my Geometry Teacher sat at an overhead projector, with large acetate films, and spent the day putting on a film, and then explaining how to create, recreate, or use what was on it. My memory hoard of Geometry is neat black and white type and a mix of red, green, and blue fine point markers explaining or using it… We each had a protractor, ruler (that he insisted on calling a ‘straight edge’), compass and pencil. That, and a bit of paper, was all we used.
Starting with two dots and a line, we proceeded to derive all of the Geometry that fit into one class year. Other students found it dull and drifted. I loved it. So much, from nearly nothing. It taught me the discipline of orderly thought (No, you can NOT just assume… NO, you can NOT use anything outside what has already been proven. NO, what you THINK you KNOW is not enough…) along with a love of minimalism. To this day I strive for the most understanding from the minimum possible assumption set. (In assumptions there is error… another learning… or at least uncertainty… another learning, or…)
At the end of the year I appreciated the 3? thousand years of thought that had been gifted to me and the purity of soul that pursued it.
So that above quote touched my inner core of reason. So simple, so few assumptions, so clearly stated. Tiny things in large numbers have gigantic surface areas. What chance does one square meter of surface stand against 2400 sq. m. of rain? (Or the 10s of thousands of m^2 of mist…)
Then there are clouds… same issue on steroids.
It is that which causes me to think this is worth preserving…