The complex and numerous forms for snowflakes result from various steps in their development. Generally, a snowflake starts out as a microscopic dust grain floating about in a cloud. Water vapor within the cloud begins to condense around the dust grain. Eventually, the droplet freezes into a six-sided (hexagonal) ice crystal. The hexagonal shape is determined by the angle that two hydrogen atoms and one oxygen atom bond together to form a water molecule.
The ice crystal continues to grow six tiny branches, narrowing as they expand. They develop differently depending on changes in the surrounding humidity and temperature. As the ice crystal falls through the cloud, it joins together with other ice crystals, influencing the growth of the branches. If the group of ice crystals fails to fall to the ground, they continue to be called ice crystals. However, if they fall to the ground, they are called snowflakes. An average snowflake contains hundreds of ice crystals. Snow forms when snowflakes combine together.
Most snowflakes are less than 0.5 inch (12.7 millimeters) in diameter and the smallest are only 0.003937 inch (0.1 millimeter). Under the best conditions for forming snowflakes, they may grow to irregular shapes that are nearly 2 inches (50.8 millimeters) wide.
Studies performed by cloud physicist Jon Nelson at Ritsumeikan University in Kyoto, Japan, and other researchers around the world have found that ice crystals could have a dramatic impact on global climate changes, specifically ozone depletion. These scientists contend that ice crystals act as a mechanism (catalyst) to increase the speed by which ozone breaks down. (Ozone consists of three oxygen atoms. It is a naturally occurring molecule found in the Earth’s atmosphere.) They also state that ice crystals in the atmosphere could play a critical role in generating electrical charges in clouds, thus, helping to produce lightning.
Nelson says that each large snowflake is most likely different, while the smallest ones could very probably be identical (when viewed under a microscope) because they have had little or no chance to grow and, thus, to make themselves unique.
Just how snowflakes influence climate and weather is unclear to scientists. Additional research is being performed to understand the relationship of snowflakes and global climate conditions.
To view the general mechanism by which snowflakes are formed, go to the American Chemical Society Web site at: http://acswebcontent.acs.org/journalist_resources/snowposter.pdf.
The research paper published by Dr. Jon Nelson in the American Chemical Society journal Crystal Growth & Design, which explains snowflakes in more detail, appears at: http://pubs.acs.org/cgi-bin/sample.cgi/cgdefu/2005/5/i04/html/cg049685v.html.