Why Clouds are White--Part 1.75

In the service of clouds: my latest library haul to answer a basic question.

This is Richard Feynman's friendly question in his lecture, "Radiation Damping. Light Scattering."

This was his unfriendly answer. I get it, but not really. So I found a different book.

This is from Why the Sky is Blue by Gotz Hoeppe.

As is this...which made some sense, but is certainly uncloudlike.

This neat chart shows the relative sizes of particles in the atmosphere compared to wavelengths of visible light.

Look how much bigger they are than... the lines at the top! Huh?

I kept reading and was greatly encouraged by the "made simple" pitch.

Oh, but it wasn't simple at all. In the penultimate paragraph of this long chapter , the author stated: "The reason is simply that these particles are too big to big to be electrically polarized as a unit by an incoming light wave, and this prevents them from becoming oscillating dipoles."

This sure is simple.

I think the answer might be in here.

But I am going to need a shrinky drink. (Image source: wwww.victorianweb.org)

The Force of Fiction

   This is a work of fiction on par with Joyce's Ulysses in terms of complexity, style, mastery of language, and inventiveness. I am two-thirds of the way through. I do not think it is about clouds. (I bought it because I judged a book by its cover).
   In my present struggle with atmospheric pressure, I had to laugh at this:

"Funny, thinks Milton. Power, time, gravity, love. The forces that really kick ass are all invisible."

Physics of Clouds

   I am reading a book on physics and clouds, sort of. On page six, the author writes that  a friend of hers "likes to ask the following 'science' question.: How would you hold a hundred tons of water in thin air with no visible means of support?'"   The answer is the book's title: First You Build a Cloud. Such an elegant solution  especially given the next-best alternative (above, in two convenient sizes).

If you do build a cloud, start small.

   A cloud can hold 350,000,000,000 tiny droplets of water per cubic foot. A medium-sized cumulus cloud can weigh in somewhere between 320 and 480 tons--about as much as 80 elephant (each weighing 4-6 tons), according to several sources. Most of these sources acknowledged that you cannot actually weigh a cloud and that clouds are actually less dense than dry air, which is why they "float."

Imagine the weight of this cumulus congestus cloud! A veritable stampede of pachyderms in the sky!

 

   First You Build a Cloud and Other Reflections on Physics as a Way of Life is the full title of K.C. Cole's marvelous book--one that makes "general audience" readers like me feel less intimidated by a book with the word "physics" in it. 

   Cole's book is arranged in three parts: The Art of Knowing, Movers and Shakers, Threads and Knots and is full of insights, analogies, metaphors, enthusiasm, and awe for the physical world and the science of physics...which is more philosophy, poetry, and sentiment in Cole's capable hands. Aside from the riddle about the cloud and the lovely cumulus on the book's cover, Cole explores ideas and themes close to this cloud lover's heart: Why are things the way they are? Why do they behave the way they do? How science "provides us a handle on who we are and how we fit into the scheme of things." The role and limitations of mathematics, seeing, language, and metaphor in science. The value of being wrong and why wrong really mean wrong, but limited.
  Cole was a longtime science writer for the Los Angeles Times and now teaches at USC's Annenberg School of Journalism. In her book, she brings out the lighter sides of physicists such as Richard Feynman, Victor Weisskopf, Albert Einstein, J. Robert Oppenheimer and Frank Oppenheimer (former director of the Exploratorium who appears in the book as 'my friend the physicist").
  "Some people say that subjects like gravity or the states of matter [or clouds!] are too fundamental to be interesting," Cole writes. "People today are too sophisticated. Yet it's amazing how easy it is to be clueless even in this most technical of modern worlds. 'Most of us are in daily contact with at least as much that we do not understand as were the Greeks or early Babylonians,' my friend the physicists liked to say. 'Yet we have learned not to ask questions about how the power steering on our cars works or how polio vaccine is made or what is involved in the freezing of orange juice [or why clouds are pink at sunset!]. We end up in the paradoxical situation in which one of the effects of science is to dampen curiosity.'"
  Cole writes with clarity and ease and her book (published in 1999) will spark your curiosity and make you feel as though Einstein, Newton, Kepler, Oppenheimer, and the gang were all your chums.

The Sky is Crying

Because I am temporarily bereft of William Frey's book on crying, I am now perusing another book, Crying: The Natural and Cultural History of Tears, by Tom Lutz (Norton, 1999).
In my last posting, I promised to share my discovery of what exactly makes us cry—the metaphorical equivalent of the condensation nuclei (airborne dust, grit) water vapor condenses on to form a water droplet that may, under the right conditions, become visible to us as a cloud. I knew finding the answer or answers wasn’t going to be easy and that I would probably have to learn something about how tears are formed. I had written paper on the eye in elementary school (sadly, 5th, not 1st grade). I still have this paper and bring out occasionally to read to my family while cringing, laughing (and weeping) at my very unscientific approach to my topic.
Here is what I had to say about tears in my paper, written in my favorite blue felt-tip pen and in all caps:

“IF THE EYE IS VERY DRY OR SOME GERMS GET IN THE EYE, THE TEARS WILL FORM, BUT THEY WILL NOT APPEAR ON YOUR CHEEKS BECAUSE THERE ARE TWO CANALS BELOW THE EYE THAT CARRY THE TEARS OFF INTO THE NOSE. [LOL] THE TEARS WILL COME FROM THE TOP OF THE EYE AND RUN DOWN TO THE LOWER EYELID AND GO TOWARD THE NOSE UNTIL IT REACHES THE NOSE. IT WILL GO INTO THE CANAL AND INTO THE NOSE. IF A FOREIGN OBJECT GETS INTO THE EYE AND CAUSES PAIN OR EMOTIONAL STRESS THE TEAR GLAND WILL 'OVERFLOW' SO IT WILL PRODUCE TOO MUCH LIQUID WHICH WE CALL 'CRYING.'"

Wow.
I seem to be describing some kind of sewage system terminating at the nose.

In fact, the system in the body that produces tears, the lacrimal system, has secretory and excretory functions. That is, it produces tears and drains them away, so while the sewer metaphor is unfortunate, it is partially apt. The lacrimal system includes glands and ducts connected to a network of ganglia and nerves in the brain and spinal cord. Lutz's diagram of the lacrimal system (below, sorry about the focus) is not unlike a weather chart; the lines and direction arrows of neural pathways resembling the lines meteorologists use to indicate the direction and flow of frontal systems across the earth’s surface.

Not to force a metaphor, but dern if Lutz’s illustration of the lacrimal gland and excretory ducts (below) does not resemble a drawing, albeit a primitive one, of a cumulonimbus cloud with rain falling from its base. It even looks like it’s watering a tidy “lawn” of eyelashes!
Since I am interested in how tears are formed not drained, I will focus on the lacrimal gland and avoid the nose since, as I think you will agree, I gave it a pretty thorough treatment in my paper.
The main, cloud-like lacrimal gland is located between the frontal bone and the eyeball and, in conjuction with more than eighty much smaller lacrimal glands, produces basal tears continuously at the rate of 5-10 oz. a day. Basal tears lubricate the eye. Some of the basal tears evaporate between blinks of the eye and some is drained through the puncta—the little pink bump on the nose side of your eye where errant gnats often end up, drowned. From the puncta, the tears flow into the lacrimal sac (which looks just like a drainage canal!) and then into the nasolacrimal sac (another canal!) which empties into the…nose.

Now my mind has completely de-railed and I am thinking of re-writing Nicolai Gogol’s satirical short story, “The Nose,” as a tearjerker. Luckily I have my book of Gogol stories on my shelf downstairs; luckily, after re-reading the first few pages, I decide not to take on Yakovlevich, Kovalyov, and the evils of Russia’s upperclass symbolized by a giant snubbing nose.

Back to tears. In addition to producing 5-10 oz. of basal tears, the lacrimal glands produce exceptional quantities of emotional tears (I am hunting for estimates of exact quantity) causing the puncta to runneth over. Onto the cheeks.

Meteorologically, the runneth over part is the rain. At what point does a cloud runneth over? Several types of clouds produce rain, so my explanation here is simplified. According to my Main Rain Man, Michael Allaby, in his fabulous Encyclopedia of Weather and Climate, a cloud droplet 0.0008 inch across must increase its volume more than million times to attain the size of a raindrop 0.08 inches across.

Depending on the temperature inside the cloud, water droplets grow to this size by colliding with each other or by freezing into aggregations (snowflakes). When droplets are at least 0.04 inches across, gravity gets the best of them and they begins their descent from the base of the cloud to the earth. These droplets are still potential, not actual, rainfall. Like sad thoughts you can stifle before you choke up and get teary, some rain evaporates before it reaches the ground. Raindrops or ice crystals that fall from or are left behind a cloud but do not reach the ground are called virga (below).

Alas, dear reader, I must leave you here--high and dry--as I am now over my head in cloud physics. When I can explain to myself how exactly a cloud droplet becomes a successful, ground-reaching raindrop, I will let you know. Promise.