Who else is dreaming of a white Christmas? (emphasis on dreaming as opposed to seeing). Snow can be the most idyllic feature of the winter holidays. There’s plenty of countries that do it better than us, but snow covered ground can go beautifully with some of the UK classic towns and winding countryside. Let’s take a look at the physics behind snowflake formation and what give it its beautiful structure.
What makes up a snowflake?
We shall start with a bit of technicality. According to scientists, it is more accurate to use the term ‘snow crystal’ rather than snowflake. Snow crystals involve a single crystal of ice, while snowflake can mean individual or multiple snow crystals joined together, or even large quantities of snow crystals in the form of ‘puff balls’.
One misconception surrounding snowflakes is that they are frozen raindrops. Frozen raindrops, which are formed by liquid in the atmosphere freezing and descending to earth, is actually just sleet. Hail on the other hand is a large piece of sleet which collects more water as it falls to the ground.
How does it form?
The atmosphere holds tiny particles of water in the from of water vapour. As the atmosphere cools during the winter months, this water vapour will condense or pack closer together to from water droplets. These droplets then freeze when the temperature falls below 0˚C, forming snow crystals. These snow crystals either fall to the ground individually or from snowflakes with up to 100s of other snow crystals. The shape of a snowflake is due to hydrogen bonding. Without getting too deep into the science involved, hydrogen bonding is a product of the intensely strong attraction between very negatively charged oxygen and highly positively charged hydrogen. Because of the hydrogen bonds, snowflakes form a reputed hexagonal pattern. There is however a large number of shapes the snowflake can form, but no matter what it will always be symmetrical.
Are any two snowflakes the same?
The shape of a snowflake comes from environmental conditions. These include humidity and temperature difference between the expanding ice crystal and surrounding warmer air. Most snowflakes will have a common underlying cristal structure. However, the direction in which ice crystals can grow becomes limited as they get bigger. This same principle explains a variety of natural patterns occurring on Earth, such as the way branches on trees grow. As temperature and humidity alter, the crystal growth occurring will alter as well. Because of this, scientists are able to find the conditions in which snowflakes first formed by looking into the centre of the crystal. Small temperature changes can lead to a remarkable change in snowflake shape. Thin plates and star shapes form at both -2°C and -15°C, whilst columns and needles form around -5°C. Humidity also plays a factor, with snowflake complexity increasing with increasing humidity. See the figure below for details.
Why snowflakes transition from plates to columns depending on the temperature is still a scientific mystery. Snowflakes are not exactly symmetrical; by looking closely at snowflakes, the arms can be slightly different on either side of the flake. This is due to the fact that they tend to oscillate as the wind blows them around.
So, are any two snowflakes the same? The true answer is — it is incredibly unlikely. There are many factors which affect snowflake formation. The likelihood of all of these conditions being exactly the same for any snowflake is very low. It’s similar to throwing a packet full of sweets on the floor over and over again until the exact spread of sweets occurs more than once. It is statistically possible, but you could be doing it billions and billions of times over and not necessarily getting close to repeating the same results.
SEE ALSO: Engineering the perfect snowman
Originally published at ilmm.co.uk on December 28, 2016.
