Therefore, it is not easy to encounter the right type of aerosol under the ideal climatic conditions! But when things align well, we find ourselves in the presence of a fabulous primary snow crystal. Credit : Kenneth Libbrecht - ThreadSky

locuste.bsky.social • 92 days ago

Therefore, it is not easy to encounter the right type of aerosol under the ideal climatic conditions!
But when things align well, we find ourselves in the presence of a fabulous primary snow crystal.
Credit : Kenneth Libbrecht

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locuste.bsky.social•92 days ago

Although it starts as a tiny ice grain (and for good reason, it doesn’t exceed a few millimeters at most), it will have the opportunity to grow by drawing water molecules from the surrounding water droplets !

Now, I guess the persistence of these droplets might seem completely absurd to you,

locuste.bsky.social•92 days ago

because we are in a cloud with negative temperatures. Shouldn’t the water freeze under these conditions ?
Well, actually, no ! Even below 0°C, water droplets will remain liquid.This paradox, which is troubling for our minds, actually corresponds to a particular state of matter called supercooling.

locuste.bsky.social•92 days ago

In such a state, water droplets can remain liquid at temperatures below 0°C, up to a limit that nature has set around -40°C.

However, since it is an unstable state, the slightest external disturbance (imagine contact with a surface or a particle, for example) will be enough to trigger

locuste.bsky.social•92 days ago

their immediate transition to the solid state. We will see later examples of situations that cause this sudden change, but for now, let’s continue with my story.
As I mentioned, the snow crystal develops by inheriting water molecules that belonged to the neighboring droplets.

locuste.bsky.social•92 days ago

So, if necessary, I prefer to warn you against the temptation to attribute any will to the snow crystal: no, I assure you, it is not consciously stealing the droplets to grow at their expense!

In reality, this transfer of water molecules is a natural process called the Bergeron effect.

locuste.bsky.social•92 days ago

It is triggered spontaneously due to the difference in humidity between the air around the crystal and that in the droplet zone.

Once in action, it induces the gradual evaporation of the droplets, and the water vapor thus formed joins the crystal, freezing onto it in turn (it should be noted that

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