Clouds

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Naveen's two cents

Actually, there must be some interesting physics involved to produce the wide range of shapes of clouds. For instance, why do some appear to have boundaries, instead of simply diffusing? A less-than-reliable (i.e. not peer-reviewed) source raises some interesting questions about what causes clouds (see [1]). Water droplets are much denser than water, so even updrafts of wind or atmospheric drag forces would not be enough to suspend them. Instead, the author claims that the air between water droplets is warmed by the heat of condensation when the water vapor forms a suspension in the atmosphere. However, even this additional information does not explain the morphology of clouds.

Another non-journal article about the physics of clouds [2] explains how some aspects of clouds are fractal-like due to atmospheric turbulence, but daily temperature cycles, spatial variations in the earth's surface (e.g. land-sea boundary), and Benard cells [3] can introduce additional structures.

On the electrical structure of clouds

In general, clouds have a net positive charge towards the top, and a net negative charge towards its center. There is also a net positive charge towards the bottom of the could present in some clouds. This charge net charge distribution generates an electric field inside the cloud. Several groups have studied these electric fields both from the charge and the from the air. Of course, when lightening occurs, these fields change dramatically.

Question for thought: If we have polar water molecules in an electric field, wouldn't the interaction between the water droplets and the electric field within the cloud be the dominant interaction within the cloud rather than the dipole dipole interactions between the water droplets?

Good reads

I found several good and thorough books about clouds..


I was browsing through and found this book in Cabot:Atmospheric chemistry and physics : from air pollution to climate change / John H. Seinfeld, Spyros N. Pandis. It has quite a few chapters about clouds, but I can't seem to find a copy of it online.


Another good and really thorough discussions about cloud is found here: Microphysics of Clouds and Precipitation By Hans R. Pruppacher, James D. Klett[4]

I wanted to summarize some of these chapters, but realize that it is probably better to refer the books to you guys! Unfortunately, some of the more interesting chapters (ie. Chapter 15). Mckay has the book, but it is checked out.


Also: Cloud dynamics by L T Matveev [5] Available online and in Mckay.


These hopefully should answer all the questions that anyone have about clouds!!

Biology enters!

Last week Brent Christner, assistant professor of biological sciences at LSU, published in PNAS findings that elucidate the role and source of bacteria in nucleating ice crystals in clouds. The following is a newsy article on the subject, and the paper recently published online at PNAS can be found here.

I imagine that makes them quite soft and, dare I say, a complex fluid.