COLUMBIA, S.C. — Winter mornings are characteristically cold and typically involve frost on the ground, but did you know that not all water freezes when the temperature drops below 32 degrees?
In meteorology, we call these drops of water supercooled water droplets and they are a pretty common occurrence in our atmosphere. They are also pretty easily replicated in this experiment. All you need is an unopened bottle of purified water and a freezer.
Here's what you want to do:
- Gently place the bottle of water in the freezer
- Leave the bottle untouched in the freezer for between an hour and a half and two hours
- Once the time is up, carefully remove the water bottle from the freezer, it should be all liquid
- To create "instant ice" and freeze the supercooled water, simply shake the bottle or hit it against a counter
You should be able to see the water all turn from a supercooled liquid to an icy mixture!
Now, why does this happen? Water droplets typically need something to "stick" to, which we call condensation nuclei in meteorology. This could be a small piece of dust or dirt or pollen floating in the sky. When water is "pure" and does not have anything to stick to, it will not be able to as easily freeze. So our undisturbed water was able to chill below freezing until we gave it something to "stick" to.
This happens up in our atmosphere too! There are tiny droplets of supercooled water suspended in the air in certain types of clouds and setups. In order for them to freeze, they need something to disturb them or something to stick onto.
One of the most common setups we see with these droplets creates a cloud called a hole punch cloud or a fallstreak hole. This occurs when an airplane moves through a layer of supercooled water droplets. These droplets all freeze on the exhaust from the airplane and fall, creating a hole punch look to the clouds.