Everyone knows that no two snowflakes are identical to one another. That's because they all start out as a simple hexagonal prism - the most basic form of snow crystal - but then encounter a range of atmospheric conditions as they journey down to Earth.
It was two Japanese physicists who made early strides in our understanding of snowflake formation. Ukichiro Nakaya at the University of Hokkaido in the 1930s and Takehiko Gonda in the 1970s at the Science University of Tokyo found that humidity, temperature, air pressure and other conditions are the variables that determine the shape of a snowflake.
Kenneth Libbrecht writes, “Although no two crystals end up exactly alike, the six arms of a single crystal all travel together, so they all grow in synchrony, giving each falling crystal a unique and intricate structure with a recognisable symmetry.”
The conditions in the atmosphere dictate how water molecules are transported to the crystal but, because of the infinitesimal range of conditions, that makes it hard to simulate snowflake growth and explain how particular structures are formed.
Numerical modelling is now being used to reproduce the complex structures. The work is of particular interest to metallurgists as a better understanding of snowflake structures could profoundly affect the strength and ductility of their own final materials on a micro- or even nano-scale.
Libbrecht continues, “Beyond the intrinsic scientific questions, beyond the practical applications of crystal growth, and beyond the meteorological significance of atmospheric ice, we who ponder snowflakes are motivated by a simple and essential desire to comprehend the natural world around us.”
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