15 December 2009

Have You Ever Seen an Ice Ribbon?

Posted by Dan Satterfield

Joe Vaughn has.

I received an email over the past weekend with a picture and a question. What is this??

Ice Ribbon- image by joe Vaughn Huntsville,Al

Ice Ribbon- Image by Joe Vaughn at Huntsville, in Alabama

What you are looking at is an ice ribbon. They are also sometimes called a frost flower. It’s been about a decade since a viewer sent me a picture of one. I have only seen them myself once.

So what are they? Are they natural? Are they really ice?

The answer is yes. They are ice and they are indeed natural.

They form when liquid water inside a stem seeps out into the open air and freezes. Capillary action inside the plant pumps more water out so a continuous stream of ice is formed. Almost like a tiny glacier!

So why does the water inside the plant not freeze too?

The most likely answer is that the water is coming up from the ground where the temperature is above freezing. If the water is under pressure, the freezing point is lower so the water could be super cooled. Water only freezes at 0C at standard atmospheric pressure of 1013.25mb (29.92” of Hg on the old scale).

You can even get pure water down to -20C in your freezer if you freeze it very slowly in a clean container with no movement. Once any piece of dust or crystal is introduced it will suddenly freeze in front of your eyes! Even changing the pressure slightly will trigger an instant freeze as crystals form in rapid succession.

(They don’t get it, but you do!)

Supercooled water is the rule in the atmosphere, not the exception. Many clouds you see are made up of water droplets that are well below freezing and yet still liquid. If it were not for dust and other atmospheric aerosols, cloud drops would rarely coalesce into the much bigger rain drops that give life to the land below.

We are used to living in a world where the pressure is near 100 hectopascals of pressure and the temperature between -10 and 40C. If we lived in a world that deviated from these norms, we would see many, many things that we would call strange, yet are perfectly normal! I will not live long enough to witness the exploration of the planets in our solar system and beyond, but I cannot imagine the strange objects and sights that await future explorers.


The other climber is in shadow.

Here is an example. I took the picture above of two ice climbers in the Canadian Rockies. They were about 1500 meters away. (Zoom lens). The temperature was -25C and the wind was dead calm.

So what was so unusual?

The two climbers were talking to each other and I could hear them clearly. They were talking in a normal tone of voice and I could hear them easily 1500 meters away! The sound was reflected by the frozen ice and traveled a long way in the calm and frigid air.

These frost flowers tend to happen after a heavy rain event in mild weather. A sudden blast of arctic air will bring air temperatures well below freezing, but the ground will stay warm. The sudden freeze will cause water in stems to freeze and expand. This causes tiny slits to form in the stem. The warm water then seeps out of the slits due to capillary action. The water freezes quickly in the cold air and forms the ice ribbons/frost flowers. (Addition: Cool video for fellow geeks interested in capillary action in terms of physics.)

This exact sequence of weather happened here in the Southeast USA this past week. The result is that Joe Vaughn who has been hiking the beautiful mountains around the Huntsville area for many years, got a real surprise!