Cloud Making

Spontaneous freezing point

I first became aware the trifecta of genes, bacterial-decomposition, and cloud micro-physics in the early 1980s. CED first reported on ice-nucleating epiphytic-bacteria on April 1, 1992. At that time there were more than 400 journal articles on biogenic ice nucleation. Since then I have lost count. In 1995 the first compendium on the subject was published. The first chapter is on the Principles of Ice Nucleation is authored by Gabor Vali. The last chapter, is titled: “Applications of Biological Ice Nucleators in Spry-Ice Technology.”

Think Skiing and Think Big Bucks

Biological Ice Nucleation and its Applications. Edited by Richard Lee, Gareth Warren and Lawrence Gusta. Published by The American Phytopathological Society.

While we are recommending books for your summer reading, I offer one on ice with the title ICE and sub-titled: The Nature, the History and the Uses of an Astonishing Substance. By Mariana Gosnell (2005) Alfred A. Knoff, New york.

Gabor Vali, Department of Atmosphere, University of Wyoming, Laramie, Wyoming
R, C. Schnell, National Center for Atmospheric Research, Boulder, Colorado

Heroes both!

The story begins. Cloud gazers sometimes search for dragons, pigs and in-laws type relatives in the happenstance of cloud morphologies.

Others look into the details of it all. Summer thunderstorm viewers know that clouds take on a bubbling cauldron-like looks: cauliflower head. As the thunderstorm grows upward, cloud air and cloud droplets cool. Droplets phase change to ice crystals and the cloud edges are fleecy and the cauliflower head appearance is long gone. The temperature at which this change occurs can be as warm as just below freezing or cold as low as - 40C! At this spontaneous freezing point, the super-cooled cloud droplets, all by themselves, convert ice crystals. At warmer temperatures (> - 40 C), ice crystal formation depends on decomposition of organic matter down on the ground! For ice crystals to form at say between 0 C and -10 C lots of decomposition probably occurred somewhere below the air and got fed into the thunderstorm in updrafts. These substances are called ice nuclei. You guessed it. This is another little vegetation-controls-climate pieces and in this case a vegetation-controls-weather story as well.

We now have both homogeneous icing at – 40 C and heterogeneous icing when temperatures are warmer than – 40 C. It is these heterogeneous materials that we are starting to learn about in this blog. There is more to come in subsequent blogs.


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