Wednesday, February 22, 2012

Snowflake Sensation!

While aesthetically appealing and offering a striking subject for photography, the fact is that most ice crystals are defective and irregular in shape to varying degrees - Bailey and Hallet (2009)

When most of us think of snowflakes, we think of beautiful, symmetrical crystals.  Indeed, it is possible to grow such snowflakes in a lab or, with effort, to find them in nature.  Nobody does a better job of this than Ken Libbrecht at Caltech.  Some samples from his spectacular web site are below.  

However, as suggested by the quote above, most natural snowflakes are defective or, if I may use a scientific phrase, "beat to hell."  In addition, there's an unbelievable variety of snowflakes in any winter storm.  

One of my colleagues at the University of Utah, Professor Tim Garrett, is leading the development of an truly incredible Multi-Angle Snowflake Camera (MASC).  Other University of Utah contributors are Cale Fallgatter and Konstantin Shkurko.  With help from Dan "Howie" Howlett and the Center for Snow Science at Alta, the MASC is currently operating at Alta Ski Area and collecting images during winter storms.  They are mind boggling.

What makes the MASC unique is that it takes images of snowflakes in freefall.  There is no impact, and the fall speed of the snowflake can also be measured (this has some science applications, including some related to numerical weather prediction).  The MASC can take thousands of images, enabling an unprecedented survey of the snowflake diversity during winter storms.  Here are some images from earlier this month.

Source: Tim Garrett,
One can see the "defective and irregular nature" of the snowflakes, as well as varying degrees of riming.  Clouds that produce snow in Utah are what we call mixed phase, meaning that they are a mixture of ice particles and liquid water droplets.  The liquid water droplets are supercooled, meaning that they are below 0ºC (32ºF), but not frozen.  These droplets, which are very small, freeze when they come in contact with an ice crystal.  This is what we call riming.  The images above show snowflakes that have been rimed to varying degrees.  The images at top right and center right are what we call graupel, an ice crystal that has been so heavily rimed it is shaped like a ball, lump, or capsule.  

Get your geek on and check out the MASC images at  Tim is hoping for a live feed soon.  

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