Thinking about ice on a HOT day

Good grief, its already 88 F at 5 AM here in Catalina!

With a whole stretch of 100 F plus days ahead, maybe it would be good if we looked at some ice and thought about it.  Below are some ice crystals, as photographed by Magono and Lee (1966), a publication that is thought of as the “bible” of ice crystal classifications.   If you did or do field work on snow, in the air or as it fell to the ground, you likely classified the ice crystals that you saw as suggested by these venerable researchers.

Ice crystals have different shapes and different temperatures and saturation levels in clouds.   Magono and Lee classified those shapes by temperatures and saturation levels at which they formed, and you can see some that in the pages shown here:   Magono and Lee When you saw an crystal with a particular shape, or if it had frozen cloud drops on it, you then knew something about the temperature and humidity at which it formed;  that crystal’s history so to speak.

“Factoid”:  Nearly 100 percent of all rain that falls on us here in Catalina is that due to snowflakes, hail, soft hail (called “graupel”) that have melted on the way down.   For example, those huge drops that first fall out of that big, dark cloud base right above you are without doubt melted hail or “graupel.”

As you examine at these natural ice crystals in detail, thoughts of cool air should come rushing over you.   This is because the air in which these crystals formed would have to be cooler than  about -4 F (24 F), the highest temperature at which a natural ice crystal can form, and even then, those only under special conditions.

I suggest meditating on each photo.

In general, the ice crystals shown below go from higher formation temperatures to lower ones.    The first ice crystals shown, for example, are “needles.”  They form at temperatures between -4 and -6 C.  These are temperatures that moderate-sized Cumulus congestus tops sometimes reach, or winter Stratocumulus clouds. An example of using this knowledge in our module of “Converstional Meteorology” would go something like this.    Lets say on a winter’s day, deep and dark in December (why does that phrase sound familiar?) that you saw some “needle” ice crystals falling on your dark jacket at the top of Mt. Sara Lemmon.   The sky is cloudy in low Stratocumulus clouds, witih higher Cirrus clouds visible through the breaks in the overcast.    I have made this a bit complicated to test your knowledge.    It would be quite embarrassing for you and everyone who knows you if you then said, looking at those needle ice crystals (or even “sheath” ice crystals,  “I think these fell from those higher  Cirrus clouds we can see through the breaks in the overcast.”   Instead, you would likely know that they must have originated within the lower, warmer shallow clouds and NOT  from the Cirrus clouds overhead since the ice crystals in Cirrus clouds are mainly short stubby columns, and pointy ones called “bullets”, and sometimes in deep Cirrus clouds,  bullet rosettes, ones that look like a “bouquet of bullets”, p55 in part 2 below.  (Part 1 is ice former at higher temperatures, and part 2 are those ones that form at lower temperatures in general.)

Copies of the original photos here:




May add a bit more later, but gotta go walk a horse now…..

By Art Rangno

Retiree from a group specializing in airborne measurements of clouds and aerosols at the University of Washington (Cloud and Aerosol Research Group). The projects in which I participated were in many countries; from the Arctic to Brazil, from the Marshall Islands to South Africa.