Atmosphere And Weather

A Guide to the different Types of Snowflakes



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Snowflakes are an amazing thing. You can stare at these light, delicate crystals for hours, marvelling at their delicate beauty. No machine-produced snow even comes close.

Every snowflake has six sides, but there's many ways for six points to come together. Some snowflakes are blunt hexagons. Others look like little faceted screws. Still others are feathery six-rayed stars.

There have been many attempts to classify the different types of snowflakes. In 1951, the International Commission on Snow and Ice came up with the aptly-named International Classification System for Solid Precipitation. In addition to classifying three other types of solid precipitation, ICSI also decided that there were seven basic types of snowflake: plates, stellar crystals, columns, needles, spatial dendrites, capped columns, and irregular forms.

Later physicists and meteorologists decided this wasn't nearly complicated enough. Three years after ICSI's chart, Ukichiro Nakaya divided the falling snow into 41 different morphological types. A decade later, meteorologists C. Magano and C. W. Lee did him one better. They came up with 80 different snow crystal types.

A more practical classification of snowflakes can be found in Kenneth Libbrecht's Field Guide to Snow. He comes up with thirty-five different types of snowflake, ranging from simple prisms to arrowhead twins. His classification also includes irregular snowflakes, rime, and graupel, which is rime which has built up around a snowflake. Graupel is also sometimes called 'soft hail' because the ice builds up on something delicate instead of something hard, without destroying that centre. The result is something that looks like a fuzzy snowflake.

The most familiar type of snowflake are those which look like stars. Libbrecht identifies five types of star snowflakes: simple stars, stellar dendrites, fernlike stellar dendrites, and radiating dendrites. (Dendrite means "treelike.") There are also two crossovers between plates and stars: radiating plates and split plates and stars. This is the best-known type of snowflake because these are the largest crystals. When they land on your coat, you can clearly see their structure just by looking at them.

A special type of star snowflake is the 12-branched star. It's really a snowflake which has twinned but remained attached together. Sometimes the two twins are far enough apart that a little crystalline column grows between them.

Simple prisms look as though they have been chiselled from fine crystal. When the light catches them just right, they release colours, the same way a glass prism does.

Thin, transluscent crystals of snow fall into the plate family. Plates can be hexagonal, stellar, or sectored. Hollow plates and double plates are also possible. A rare form of plate is the triangular crystal.

Some snowflakes crystallize into tiny, frozen needles. There are three types of these: simple needles, needle clusters, and crossed needles. Slightly thicker snowflakes form capped columns, multiply capped columns, hollow columns, twin columns, and sheaths.

It is now known that many of these types of snowflakes can only form at specific temperatures. Thus, by looking at the structure of a snowflake, it is possible to guess the conditions in the clouds which formed them. Maybe one day, studying the structure of snowflakes will even give the information needed to control the weather. Until that day, snowflakes are still one of the most beautiful things in nature.

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