Friday, January 3, 2014

Microscopic Images of Snow

In honor of the cold snowy winter that much of the U.S. are "enjoying," I decided to search the internet for microscopic photos of snow.

Snow is precipitation in the form of flakes or ice crystals that fall from clouds.  Snowflakes come in a variety of sizes and shapes. Types that fall in the form of a round sphere due to melting and refreezing, rather than a flake, are known as hail, ice pellets or snow grains. 

To form, there must be a nucleus around which the water freezes.  Sometimes supercooled water droplets in a cloud freeze into a lattice, that then serves as the nucleus around which more droplets freeze.  Dust, biologic particles, and silver iodide (delivered via planes to seed clouds) can also serve as the nucleation centers.  The ice crystals gather up the abundant water vapor to grow and increase in mass.  When they are big enough, gravity takes over and the crystals fall through the atmosphere.  Since these ice crystals have an electrostatic charge, they tend to collide and stick together to form clusters, or aggregates. Once they clump together, they graduate to become snowflakes.  Although  individual ice crystals are clear, the clumped crystal snowflakes scatter and reflect the light.  Since the crystal facets and hollows/imperfections of various parts of the clump reflect the light into all of the spectrum colors which then blend together, snow on the ground appears white.

Guinness World Records list the world's largest snowflakes as those of January 1887 at Fort Keogh, Montana; allegedly one measured 15 inches wide (38 cm) wide.

The shape of the snowflake is determined broadly by the temperature and humidity at which it is formed:
--Thin, flat planar crystals form between 32 and 27 F (0 to -3 C)
--Needle and hollow column crystals form between 27 and 18 F (-3 to -8 C)
--Flat intricate dendritic crystals form between 18 and -8 F ( -8 to -22 C)
--A variety of complex crystals form below -8 F (-22 C)

In Grand Marais most of winter precipitation falls as lake effect snow.  This type of snow does not form intricate crystals or snow flakes.  It is characterized by rapidly growing crystals that are either formless spheres or elongated masses.

The world record for the highest seasonal total snowfall was measured in the United States at Mount Baker Ski Area, outside of the town Bellingham, Washington during the 1998–1999 season. Mount Baker received 1,140 inches (2,896 cm) of snow.


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